NEW PERSPECTIVES IN LUTING INDIRECT

NEW PERSPECTIVES IN LUTING INDIRECT RESTORATIONS:
EVALUATION OF THE BONDING PERFORMANCE OF SELFADHESIVE RESIN CEMENTS
Nuevas perspectivas en el cementado de las restauraciones indirectas:
Valoración de la capacidad de unión de los cementos resinosos autoadhesivos
Claudia Mazzitelli
1
University of Siena
University of Granada
School of Dental Medicine
School of Dentistry
PhD PROGRAM:
“BIOTECHNOLOGIES:
SECTION OF DENTAL BIOMATERIALS”
PhD THESIS OF:
Claudia Mazzitelli
TITLE:
New perspectives in luting indirect restorations: Evaluation of the
bonding performance of self-adhesive resin cements.
(Nuevas perspectivas en el cementado de las restauraciones indirectas:
Valoración de la capacidad de unión de los cementos resinosos autoadhesivos)
2
Academic Year 2008/2009
11th December 2009
Siena, Italy
Committee:
Promoter: Prof. Marco Ferrari
Co-Promoters: Prof. Manuel Toledano, Prof. Francesca Monticelli
Prof. Cecilia Goracci
Prof. Andrea Borracchini
Prof. Simone Grandini
Prof. Alessandro Vichi
Prof. Leopoldo Forner Navarro
Prof. Maria del Carmen Llena Puy
Prof. Zoran Vulicevic
Prof. Lorenzo Breschi
TITLE:
New perspectives in luting indirect restorations: Evaluation of the
bonding performance of self-adhesive resin cements
(Nuevas perspectivas en el cementado de las restauraciones indirectas:
Valoración de la capacidad de unión de los cementos resinosos autoadhesivos)
CANDIDATE
Claudia Mazzitelli
3
CONTENTS
Chapter 1
1.1 General Introduction……………………………………………………. 7
1.2 Introducción general……………………………………………………..10
1.3 An overview of the luting materials available for the cementation of
indirect restorations……………………………………………………. ..15
1.4 Self-adhesive resin cements: composition and properties……………….19
1.5 Self-adhesive resin cements vs cements based on multi-step systems…...22
1.6 Dentin characteristics as adhesive substrate and the influence of the
hydration state of dentin on the bonding performance of adhesive systems
and cements………………………………………………………………23
1.7 The use of fiber posts in dentistry………………………………………..26
1.8 Post surface treatments for improving the cement/post bond……………29
1.9 An overview of self-adhesive resin cements and their clinical
applications……………………………………………………………....31
References………………………………………………………………..35
Chapter 2
2.1 The interaction between self-adhesive cements and the dentin
substrate………………………………………………………………… 52
References ……………………………………………………………….54
2.2 Limited decalcification/diffusion of Self-adhesive Cements into
Dentin…………………………………………………………………….56
Chapter 3
3.1 Vital dentin as bonding substrate……………………………………74
4
References………………………………………………………………..76
3.2 Effect of simulated pulpal pressure on self-adhesive cements bonding
to dentin………………………………………………………………….77
Chapter 4
4.1 The role of smear layer on the bonding quality of self-adhesive resin
cements…………………………………………………………………..99
References……………………………………………………………....100
4.2 Dentin treatment effects on the bonding performance of self-adhesive
resin cements………………………………………………....................104
Chapter 5
5.1 Self-adhesive cements and fiber posts……………………………...126
References……………………………………………………………....128
5.2 Evaluation of the push-out bond strengths of self-adhesive resin
cements to fiber posts…………………………………………………...130
5.3 Effect of thermocycling on the bond strength of self-adhesive cements
to fiber posts…………………………………………………………….145
Chapter 6
6.1 Post surface treatments for improving the adhesive bonds…………162
References……………………………………………………………....164
6.2 Surface roughness analysis of fiber post conditioning processes…..166
6.3 Effects of post surface treatments on the bond strength of self-adhesive
resin cements………………………………………………....................182
5
Chapter 7
7.1 Summary, Conclusions and Future Directions…………..………....200
7.2 Riassunto, conclusioni e direzioni future……………………….......208
7.3 Resumen, conclusiones y direcciones futures………………………217
7.4
Zusammenfassung,
schlussfolgerungen
und
zukünfitge
ausrichtung……………………………………………………………...226
7.5 Resumé, conclusions et directions futures………………………….235
7.6 Resumo, Conclusões, Futuras perspectivas......................................244
Complete list of References……………………...................................252
Curriculum Vitae…………………………………………...................285
Acknowledgements…………………………………………………....296
6
Chapter 1
1.1 General Introduction
The clinical success of an indirect restoration is partially related to
the material and technique used for the luting procedures (Hickel and
Manhart, 2001). An inadequate marginal adaptation of the cement on the
bonding interfaces and a decreased retention mainly cause the premature
failure of a restoration (Mijör and Gordan, 2002) (Mijör et al, 2002).
A reliable adhesion is obtained when the luting agent and the
bonding substrate intimately contact. New products are continually
developed to improve and simplify luting procedures. When using
cements based on a total-etch adhesive system, the bonding mechanism is
based on the removal of the dentin mineral components as to create a
demineralized area of 1.5 µm while leaving intact the collagen fibrils (Van
Meerbeek et al, 2003). This condition is achieved using acidic solutions.
Acid-etching the dental substrate promotes the complete removal of the
smear layer thus creating unfilled spaces (Glasspoole et al, 2002). Ideally,
the resin should fulfill the voids left by the removal of the mineral content,
infiltrate the dentinal tubules and stabilize the collagen matrix, as to form
an hybrid layer between dentin and resin (Nakabayashi et al, 1982)
(Pashley et al, 1993) (Titley et al, 1994) (Van Meerbeek et al, 1992).
Hybrid layer has been considered necessary for an effective adhesion
when using cements based on multi-steps adhesive systems (Van
Meerbeek et al, 2003). However, this technique is considered too operatorand material-dependent.
7
Some variables may influence the clinical outcome of a restoration:
the operator, the design of the restoration, the materials, the intra-oral
conditions and the patient (Bayne, 2007). The first two factors are directly
related to the clinician ability. Regarding the material, it is indispensable
to understand its characteristics as well as the mechanical/physical
properties and clinical behaviours. The last two variables are related to the
patient per se (Bayne, 2007).
Self-adhesive resin cements were firstly launched to satisfy
clinician’s demands for simplification of luting procedures. These cements
are directly applied on the restoration that is then seated in place and no
treatments are necessary.
This thesis contains a study about several different aspects related to
the bonding performances of self-adhesive resin cements used to lute
coronal restorations on dentin, the influence of the hydration state of
dentin and the retentive strength of simplified cements to fiber posts. The
influence of fiber post surface treatments on the bond strength of selfadhesive cements was also taken into consideration.
The materials used for luting indirect restorations are associated to
different adhesive characteristics and bonding performances. When using
cements relying on multi-step bonding systems, limited adhesive
penetration into demineralized dentin has led to post-operative sensitivity
and decreased shel-life of the restoration (Walshaw and McComb, 1996).
A complete resin penetration into the depth of the acid-etched dental
substrate is necessary to ensure long-lasting restorations (Toledano et al,
2004). Scanning electron microscope (SEM) is commonly used to observe
the material/dentin interfacial characteristics. Good marginal adaptation of
self-adhesive cements to dentin was observed in SEM evaluations,
8
although no hybrid layer nor resin tag formations were detected (De
Munck et al, 2004) (Al-Assaf et al, 2007) (Behr et al, 2004). The first
study was conducted to evaluate the degree of dentin demineralization, the
depth of resin penetration and the quality of hybrid layer of different selfadhesive resin cements. A total-etch cement and a resin cement based on a
self-etch system were used as controls. Two combined microscopic
analysis were used: the Masson’s trichrome-staining technique for optical
microscopy and the scanning electron microscopy.
Vital dentin is an heterogeneous substrate characterized by a water
fluid flow through dentinal tubules (Marshall et al, 1997). The influence of
dentin perfusion was previously investigated on self-etch or one bottle
adhesive systems, showing detrimental effects during the initial setting
phase of these materials (Sauro et al, 2007) (Hosaka et al, 2007). The
study was conducted to evaluate the effect of an in vitro simulation of
dentinal pulpal pressure on the bonding performances of different selfadhesive resin cements. For this purpose, a microtensile bond strength test
and a scanning electron microscopy analysis were performed.
Due to the limited cement/dentin interactions, the influence of preetching steps on the bond strengths of the one-step cements to dentin was
previously investigated. It was noteworthy how dentin conditioning with
35% phosphoric acid was detrimental (De Munck et al, 2004) (Hikita et
al, 2007). Less aggressive acidic solutions could be proposed to partially
remove the smear layer and improve the bond strengths of simplified
cements to dentin. A microtensile bond strength test in combination with
the Masson’s staining trichrome technique were used for this purpose.
Self-adhesive resin cements are alternative materials for fiber post
luting. The effective sealing ability of self-adhesive as fiber post luting
9
agents is still a matter of concern (Zicari et al, 2008) (Simonetti et al,
2008). RelyX Unicem was undoubtedly the most investigated material
while little information is present regarding the bonding performances of
others differently branded auto-adhesive cements. Further studies of this
thesis have focused on the bond strength and resistance to thermal stresses
of different self-adhesive cements. In the attempt to improve the quality of
the cement/fiber post bonds, several chemo/mechanical post surface
treatments have been proposed. The topographic characteristics after the
different conditioning approaches have been studied using a confocal
microscopy and an atomic force microscopy (AFM). The self-adhesive
cement/pre-treated fiber post combinations would result in improved
adhesion and simplified techniques. A further object was to evaluate the
effects of post surface treatments on the retentive strength of selected selfadhesive cements. Push-out bond strength test and scanning electron
microscopic analysis were performed for this purpose.
1.2 Introducción general
El éxito clínico de una restauración indirecta está, en parte,
relacionado con el material y la técnica de cementado utilizada para crear
una unión entre la restauración y el sustrato dental (Hickel and Manhart,
2001). Entre los factores responsables de una posible reducción de su
integridad, se considera una inadecuada adaptación marginal del cemento
a nivel de las interfases adhesivas y una disminución de la retención de la
restauración (Mijör and Gordan, 2002) (Mijör et al, 2002).
El mecanismo de adhesión se considera eficaz cuando se realiza una
intima relación entre cemento y dentina. La investigación en el área de los
10
materials odontológicos ha favorecido el desarrollo de nuevos productos
para la mejora de las técnicas clínicas. Cuando el sistema de cementado
prevé el uso de un adhesivo de grabado total, esta unión se basa en la
remoción del componente mineral de la dentina para crear una zona
desmineralizada de 1.5 um, sin daňar las fibras de colágeno que
permanecen formando una red tridimensional (Van Meerbeek et al, 2003).
Este objectivo se logra a través de soluciones ácidas. El grabado ácido
permite, además de lo anterior expuesto, eliminar el barrillo dentinario,
que ha sido considerado uno de los factores que pueden limitar la
infiltración de la resina en los tubulos dentinarios abiertos (Glasspoole et
al, 2002). La interacción directa entre la resina con la dentina, presupone
que el material resinoso pueda rellenar los espacios dejados por la
remoción de las componentes minerales, infiltrando los tubulos dentinarios
y estabilizando la matriz de colágeno para formar una capa híbrida entre
resina y dentina (Nakabayashi et al, 1982) (Pashley et al, 1993) (Titley et
al, 1994) (Van Meerbeek et al, 1992). Desde que los sistemas adhesivos se
desarrollaron, la formación de la capa híbrida ha sido considerada el
mecanismo clave del proceso de adhesión, ya que determina una retención
micro-mecánica entre la resina y la dentina grabada (Van Meerbeek et al,
2003). De todas formas, esta técnica se considera altamente relacionada a
la abilidad del clínico así como a las caracteristicas intrinsecas del
material.
El éxito clínico de una restauración indirecta se vee influenciado por
cinco factores principales: el operador, el diseňo de la restauración, el
material, las condiciones intra-orales y la tipología del paciente (Bayne,
2007). Los primeros dos factores están directamente relacionados con la
habilidad del odontólogo. Con respecto a la elección del material, el
11
conocimiento de todas sus caraterísticas, incluyendo las propriedades
fisica/quimicas y clínicas se hace imprescindibile. Los dos últimos
factores están relacionados con el paciente (Bayne, 2007).
Los cementos auto-adhesivos han sido recentemente introducidos en
el mercado dental para satisfacer las requestas de los odontológos de
simplificación de las técnicas de cementado. Estos materiales se aplican
directamente en la superficie a adherir y no se prevé tratamiento alguno ni
de las restauraciones ni de los sustratos dentales.
El objectivo principal que se plantea en esta thesis doctoral es de
estudiar y determinar cual es el comportamento adhesivo de los cementos
simplificados recién introducidos, como se ven influenciados por el estado
de hidratación de la dentina, y la capacidad retentiva que poseen como
material de cementación de los postes de fibra, incluso tras el tratamiento
superficial de los postes de fibra a base de resina epoxíca.
Los materials utilizados para el cementado de las restauraciones
indirectas mostraron diferentes características adhesivas y diferentes
comportamentos. Una limitada penetración del adhesivo en el sustrato
dental fue observado cuando se utilizaron cementos de pasos multiple.
Esta situación provocò una sensibilidad postoperatoria y influenció
negativamente el éxito de la restauración (Walshaw and McComb, 1996).
La completa penetración de la resina en el sustrato desmineralizado es
imprecindible para asegurar una duradera restauración (Toledano et al,
2004). La metodología más utilizada para la individuación de las
carateristicas de las interfases adhesivas fue la microscopía electronica de
barrido (MEB). Cuando este tipo de microscopía fue utilizada para
observar la interacción entre los cementos auto-adhesivos y la dentina, se
notó una buena adaptación marginal del cemento al sustrato adhesivo pero
12
sin formación de capa híbrida ni de tags de resina (De Munck et al, 2004)
(Al-Assaf et al, 2007) (Behr et al, 2004). El primer estudio de esta tesi
doctoral se concentró en evaluar el grado de desmineralización de la
dentina, el grado de penetración de la resina y la calidad de la capa híbrida
de diferentes cementos auto-adhesivos. Un cemento de grabado total y un
cemento basado en la tecnología self-etch fueron utilizados como grupos
controles. El ánalisis morfologíca fue eseguido a través de la técnica
tricromica de Masson para la microscopía optica en combinación con la
microscopía electronica de barrido (MEB).
La dentina vital es un sustrato altamente eterogéneo que está
caracterizado por un continuo movimento de fluido a través de los tubulos
dentinarios (Marshall et al, 1997). Precedentemente, la influencia de la
presión pulpar fue investigada sobre adhesivos simplificados one bottle o
self-etch, revelando efectos negativos en la fuerza de adhesión, en
particular manera durante las primeras fases de endurecimiento de los
materials (Sauro et al, 2007) (Hosaka et al, 2007). El objectivo del
segundo estudio se fijó en evaluar el efecto de una presión pulpar simulada
en la capacidad adhesiva de los cementos simplificados. Para ello, fue
utilizado un test de microtensión en combinación a un ánalisi de
miscoscopía electronica de barrido (MEB).
La limitada interacción entre los cementos resinosos auto-adhesivos
y la dentina recubierta de barrillo dentinario ha llevado algunos
investigadores a testar la influencia de soluciones ácidas con el objetivo de
eliminar el barrillo dentinario y permitir un contacto directo entre
cementos y dentina. A pesar de las espectativas, condicionar la dentina con
35% de ácido fosfórico se ha relevado ineficaz cuando se evaluó la
capcidad adhesiva de RelyX Unicem (De Munck et al, 2004) (Hikita et al,
13
2007). Diferentes técnicas de remoción del barrillo dentinario, a través de
soluciones ácidas más debiles (EDTA y ácido poliacrílico), se han
evaluado, utilizando el test de microtensión asociado a un ánalisis de la
interfase adhesiva a través de la técnica tricromica de Masson para la
microscopía óptica.
Los cementos resinosos de paso único representan una alternativa
para el cementado de los postes de fibra atraendo la atención de
investigadores y clínicos. A pesar del grande interés, se observó una
limitada habilidad de adherir a la dentina radicular (Zicari et al, 2008)
(Simonetti et al, 2008), no obstante RelyX Unicem ha sido el material
perteneciente a la clase de auto-adhesivos más investigado, mientras que
algunas dudas se quedan acerca de la capacidad de unión de los demás
cementos auto-adhesivos presentes en el mercado. Los siguientes estudios
de esta thesis doctoral se focalizaron en evaluar la capacidad retentiva de
estos materiales para el cementado de postes de fibra y sus resistencia a los
éstreses termicos. Para ello, el push-out test se utilizó para evaluar la
fuerza de unión de diferentes cementos auto-adhesivos y el efecto del
termociclado en la dicha capacidad retentiva. Con la intención de mejorar
la unión a los postes de fibra, fueron propuestos diferentes tratamientos de
las superficies de los postes. Las carcateristicas topograficas fueron
evaluadas antes y post tratamientos quimio/mecanicos a través de un
ánalisis con microscopía confocal y con microscopía a fuerza atomica
(AFM). La combinación entre los cementos auto-adhesivos y postes de
fibra tratados en superficie puede resultar en una técnica de cementado
simplificada alcanzando una adhesión mejorada. Un ulterior objectivo de
esta thesis fue de evaluar el efecto de determinados tratamientos de
superficie que no demostraron de daňar las fibras de vidrio, en la fuerza
14
retentiva de los cementos auto-adhesivos. Se utilizaron la técnica de pushout para medir la fuerza de adhesión en las interfases de interés y la
microscopía electronica de barrido para caracterizar las interfases
adhesivas.
1.3 An overview of the luting materials available for the cementation
of indirect restorations
Several products are available in the dental market for the
cementation of indirect restorations such as single crowns, bridges, fiber
posts and screws. The selection of the luting agent should be based on the
specific clinical situation, the type of the restoration and the physical,
biologic and handling properties of the luting material itself (Jivraj et al,
2006). However, it cannot be possible to indicate one single product to be
universally recommended in multiple situations. An ideal luting material
should provide an effective marginal seal, it should possesses good
mechanical and physical properties, it should be insoluble in the oral fluid,
it should set in a short period of time and it has to be esthetic.
According to their chemical composition, dental cements can be
divided into five main classess: zinc-phosphate cements, polycarboxilate
cements, glass-ionomer cements, hybrid cements (resin-modified glassionomer cements and compomer) and resin cements (Diaz-Arnold et al,
1999). Clinicians should be aware of each material’s characteristics, its
advantages and disadvantages, its chemical compositions and mechanical
properties as well as the substrate to be bonded and the type of material
used for the restoration (i.e. ceramic, zirconia, composite) should also be
taken into consideration.
15
Zinc-phosphate cements, polycarboxilate cements and glass-ionomer
cements are basically water-based. They are characterized by simple
cementing techniques, but they possess limited mechanical properties and
high solubility into the oral fluids. In general, these cements can be used
for the cementation of metal and/or metal-ceramic crowns, but are not
recommended for luting resins and all-ceramic restorations.
Resin cements have improved physical and mechanical properties
and higher bond strength is established with the dental substrates.
However, they need of an adhesive system to achieve high bond strengths
and this makes the cementation technique more difficult and too operatorrelated. Resin cements can be divided according to their polymerization
mode into dual-cured (recommended for the cementation of inlays, onlays,
crowns and fiber posts), self-cured (for inlays, onlays, crowns and fiber
posts) and light-cured (recommended only for luting laminate veneers).
Another classification of resin cements is based on the number of
bonding steps required. From their first introductions in the late 1955,
adhesive systems and techniques underwent to structural modifications
and differentiations (Buonocore, 1955). At the beginning, the cements did
not require any previous adhesive application as they could establish
retention with the substrate to be bonded. Lately, adhesive systems were
selectively recommended for enamel or dentin only. To date, bonding
agents are combined to be suitable for all tooth substrates, and the
classification can be made according to the steps necessary to condition
the dental substrates (Heymann and Bayne, 1993) (Van Meerbeek et al,
2003). According to the data available into the dental literature,
simplifying luting procedures would not always be related to higher bond
16
strengths and nowadays dental research is moving to optimize the
adhesion mechanism of these materials to dentin.
The bonding mechanism is based on the concept of tissue
hybridization between the dental substrate and the material (Nakabayashi
et al, 1982) (Nakabayashi et al, 1991). The smear layer created during
prosthetic preparations, can be completely removed or partially
dissolved/modified and therefore considered as an intermediate bonding
substrate (Ayad et al, 2001) (Toledano et al, 1999). Once the dental
substrate is treated, dentin results demineralized and collagen fibers
exposed: this situation would promote resin diffusion through dentinal
tubules favouring the formation of an hybrid layer (Nakabayashi et al,
1982) (Moszner et al, 2005).
Cements relying on etch-and-rinse systems (such as Variolink,
Variolink II and Calibra) follow a three step bonding process, that is the
acid etching (necessary to remove the smear layer and to demineralize the
inter-tubular dentin and the enamel prisms), primer application (to
improve the wettability and the superficial characteristics of the substrate)
followed by the use of the bonding (Bayne, 2005). Dentin would result
more susceptible to the external physical changes after the etching
process: over-drying or over-wetting in this stage would affect the resin
diffusion and increase the probability of adhesive failures (Pioch et al,
1992) (Sano et al, 1995) (Van Meerbeek et al, 1998).
In the late 1990s, acidic monomers were incorporated into the primer
in order to assemble the etching and the primer agents in a single solution
(i.e. Panavia 21, Panavia F, Panavia F 2.0). The acidic monomers are
intended to modify the smear layer and consequently the inter-tubular
dentin; lately, the bonding should infiltrate the collagen fibrils as to create
17
an effective hybrid layer (Ven Meerbeek et al, 2003) (Breschi et al, 2008).
Clinical steps are reduced and therefore the operator sensitivity is limited
(Van Meerbeek et al, 1998) (Peumans et al, 2005).
More recently, self-etch one bottle adhesive systems have been
introduced (i.e. Adper prompt L Pop) (Moszner et al, 2005) (Nishiyama et
al, 2006). Although the interest for their easy to handling and user
friendless, their main disadvantages is represented by the chemical
incompatibility existing between the tertiary amine of the simplified
adhesives and the catalizador of the dual-cured or light-cure resin
materials (Carvalho et al, 2005b) (Tay et al, 2003a). Moreover, the
incorporation of hydrophilic monomers make these adhesives more
susceptible to the hydration state of dentin, as water can proceed through
dentinal tubules reaching the bonding interface resulting in an improper
setting reaction that would affect the durability of the restoration (Musanje
et al, 2003) (Sauro et al, 2007) (Hosaka et al, 2007). The bonds
established between highly hydrophobic adhesives and dentin would
deteriorate over time (Pashley et al, 2004) (Toledano et al, 2007).
Considering the total-etch adhesive systems, an incomplete resin diffusion
into the opened dentinal tubules was noticed (Eliades et al, 2001), showing
areas not completely impregnated at the bottom of the hybrid layer
(Pashley et al, 2004) (Hashimoto et al, 2002). This problem could ideally
be overcome with
the self-etch adhesives,
as
a simultaneous
demineralization/infiltration is expected (Toledano et al, 2004) (Toledano
et al, 2007). However, dentinal tubules were only superficially infiltrated
by simplified adhesives (Santini and Miletic, 2008) (Carvalho et al,
2005a) (Tay et al, 2002).
18
1.4 Self-adhesive resin cements: composition and properties
Self-adhesive cements are the latest subgroup of resin cements
introduced in the clinical practice. These cements include in a single
product the ease of handling of conventional cements, the auto-adhesion
and the fluoride release of glass-ionomer cements as well as the
mechanical properties, dimensional stability and micro-mechanical
retention of resin cements (Radovic et al, 2008). The less technique
sensitivity is pivotal of these one-step cements: after mixing base and
catalyst or after capsule activation, the cement is directly applied on the
adhesive substrate, hence limiting the errors that can occur with the
cement relying on multi-step systems (i.e. overwetting or overdrying the
dental substrate or the chemical incompatibility between simplified
adhesive and light or dual polimerizable resin cements) (Tay et al, 2003c)
(Pfeifer
et
al,
2003).
Self-adhesive
cements
simultaneously
demineralize/infiltrate smear layer and consequently the underneath tooth
substrate. Accordingly, smear layer represents an intermediate bonding
substrate which can reduce post operative sensitivity. In general, the
bonding mechanism of self-adhesive cements is based on a chemical
interaction and micro-mechanical retention with the adhesive substrate
(De Munck et al, 2004) (Yang et al, 2006) (Abo-Hamar et al, 2005). A
chemical reaction is established between the multifunctional monomers
with the phosphoric acid groups of the cement and the hidroxiapatite;
together, the acidic monomers interact with the alkaline fillers of the
cement complementing the chemical reaction. The water produced during
the acid-base reaction is necessary to neutralize the acidic monomers thus
favoring the hydrophilic behaviour of the material during the initial phase
19
of the reaction, resulting in improved marginal adaptation and limiting the
influence of the intrinsic wetness of human dentin. The water also acts as a
buffer solution developing more hydrophobic characteristics during the
secondary setting reaction (Radovic et al, 2008). The setting reaction takes
place following the radical polymerization that can be induced by light
exposure or through a self-cure modality (De Souza Costa et al, 2006).
However, according to recent literature data, concerns exist regarding the
efficacy of these simplified cements to set in a solely light cure mode: an
increase in monomer conversion and superior mechanical properties have
been reported after the material was dual-cured (both chemically and light
activation) (Vrochari et al, 2009) (Kumbuloglu et al, 2004) (Pedreira et al,
2009).
A wide range of self-adhesive products have been launched in the
market by different manufacturers, although RelyX Unicem (3M ESPE)
has been the first to be introduced and undoubtedly the product more
investigated. Although based on a similar auto-adhesive technology, these
materials show differences in terms of application modality, working and
setting time and chemical compositions that may differentiate their
mechanical properties and bonding performances (Saskalauskaite et al,
2008) (Han et al, 2007). Limited in vivo studies are present in literature
(Naumann et al, 2007) (Behr et al, 2008), and the knowledge of the
bonding potential and mechanical properties of self-adhesive cements is
mainly based on laboratory investigations. According to in vitro reports, a
decreased bond strength is registered when self-adhesive cements are
applied on enamel (De Munck et al, 2004) (Abo-Hamar et al, 2005)
(Hikita et al, 2007). This should be taken into consideration when luting
inlays or partial crowns in presence of a considerable amount of enamel,
20
such as for brackets cementation. Bond strength to enamel can be
increased after etching the dental substrate with 35% phosphoric acid (De
Munck et al, 2004) (Duarte et al, 2008) (Vicente et al, 2006). On the other
hand, the behavior of self-adhesive cements on coronal dentin remain
uncertain and no hybrid layer no real resin tag formations could be
observed at the dentin interface (Goracci et al, 2006) (De Munck et al,
2004) (Yang et al, 2006) (Al-Assaf et al, 2007). Although the presence of
smear layer as adhesive substrate would represent a barrier against the
direct interaction between cement and the underneath dentin, it was
noteworthy how dentin conditioning with 35% phosphoric acid did not
procure any bond strength improvement (De Munck et al, 2004). The high
viscosity of the self-etch luting agents can limits their diffusion into
opened dentinal tubules. Accordingly, Goracci et al. found that applying a
sustained seating pressure during the setting reaction of the material would
encourage the resin penetration into dentinal tubules, and increased bond
strength values were registered than when the seating pressure was not
present (Goracci et al, 2006). Although radicular dentin presents structural
differences with coronal dentin (Ferrari et al, 2000), contemporary studies
reported limited interaction between self-adhesive cements and root canal
dentin which resulted poorly demineralized and no hybrid layer was
formed (Zicari et al, 2008)(Goracci et al, 2004)(Simonetti et al,
2008)(Bitter et al, 2009).
From a mechanical point of view, self-adhesive cements showed
good resistance to compression (Piwowarczy and Lauer, 2003)
(Kumbuloglu et al, 2004) and microhardness even after immersion in
water after 3 months (Pedreira et al, 2009). The film thickness recorded
for some self-adhesive cements has been considered valid for the
21
cementation of single crowns (Kious et al, 2009), although concerns
remain on the degree of their monomers conversion and the long-term
durability of the bonds (Kumbuloglu et al, 2004)(Vrochari et al,
2009)(Mese et al, 2008). Partial polymerization would increase the
solubility of the cement particles into fluid solutions, favoring the
occurrence of cytotoxic effects and pulpal damages (Ulker and Sengun,
2009)(De Souza Costa et al, 2008).
1.5 Self-adhesive resin cements vs cements based on multi-step
systems
Contrasting results were evidenced when the bonding performances
of self-adhesive composite cements were compared to those of
conventional and/or resin cements that rely on multi-step adhesive
systems. When used for the cementation of ceramic crowns, the marginal
adaptation of RelyX Unicem was comparable to that of a self-etch system,
a total-etch cement and a compomer, revealing a lower dye penetration,
notwithstanding the scarce hybrid layer and resin tags formations (Behr et
al, 2004). The interfacial characteristics of the self-adhesive cement/dentin
interfaces were inferior when compared to those of well-tried systems (AlAssaf et al, 2007) (De Munck et al, 2004), although the bond strength of
self-adhesive cements to dentin would be considered more crucial (Bitter
et al, 2008).
Ageing simulations were claimed to be important sources for the
understanding of biomaterials properties. According to the data present in
literature,
total-etch
cements
showed
the
higher
resistance
to
thermo/mechanical stresses than self-etch systems and self-adhesive
22
composite cements. Conversely, results of other investigations revealed
bond strengths of self-adhesive cements comparable or higher to
conventional cements after thermocycling.
Compared to conventional resin cements, Max-Cem revealed to be
highly dependen to mixing errors, that would jeopardize the final adhesion
process (Behr et al, 2008). However, the bonding performances of a
material seemed related to the material chemical composition itself.
Comparisons are usually difficult to be done as the same self-adhesive
cements showed differences in their chemical composition and different
bonding behaviour (Han et al, 2007) (Skalauskaite et al, 2008). A more
complete classification of self-adhesive cements is warranted in order to
determine the class and to deeply understand their adhesion mechanism.
1.6 Dentin characteristics as adhesive substrate and the influence of
the hydration state of dentin on the bonding performance of adhesive
systems and cements
The dentin is an host substrate to be bonded, due to the structural
differences existing between the different regions and the physiological
problems. Dentin surface treatments and new materials are continuously
experimented in order to improve the adhesive strength to this variable and
heterogeneous substrate. The knowledge of the main components and
mechanical properties of dentin is imperative to face to this substrate and
develop dental biomaterials able to substitute the lost tissue and to
physiologically integrate with the rest of the dental tissue (i.e. enamel,
cementum). These procedures are intended to limit the effects of micro23
and nano-infiltration which can determine a premature failure of the
restoration (Marshall et al, 1993a).
Different types of dentin can be distinguished: primary, secondary,
reparative, tertiary, transparent, carried, demineralized, remineralized or
hypermineralized (Marshall, 1997). In fact, dentin is an highly complex
and heterogeneous substrate dissimilar from the others dental tissues. It is
formed of its 50% of vol of mineral components, 30% of organic matrix
(in particular, type I collagen fibers) and 20% of fluids (Ten Cate, 1994).
Dentin is an elastic tissue for the above enamel, while it has to protect the
underlying pulp tissue. Differences exist between the superficial and deep
dentin in terms of morphology and chemical constituents (i.e. number of
dentinal tubules and their dimensions, the peri-tubular dentin and the areas
occupy by the inter-tubular dentin) (Urabe et al, 2000) (Toledano et al,
1999) (Pashley, 1989). Originating from the pulpal tissue, the dentinal
tubules go along a radial orientation. Both tubules density and their
diameter undergo to a reduction follow the proximity of the superficial
dentin. The orientation of dentinal tubules can influence the mechanical
properties of the substrate (i.e. being situated perpendicularly would result
in a reduced strength to the occlusal forces) (Arola and Reprogel, 2006).
The mineral component is found among the inter-tubular and peri-tubular
dentin (Marshall et al, 1993a). The dentin hydroxiapatite crystals show
differences when compared to those of the enamel, as they are smaller,
contain an inferior percentage of calcium and a reduced amount of
carbonate (4-5%) (Posner and Tannenbaum, 1984) (Jones and Boyde,
1984). The hydroxiapatite crystal anchor to the dentinal tubules (Hayashi,
1992) and this union play an important role in establishing the mechanical
24
properties of dentin (Marshall et al, 1993a) (Marshall et al, 1997) (Urabe
et al, 2000).
Different from the enamel, vital dentin is known to be highly
hydrated, as it is characterized from a continuous water fluid-flow through
dentinal tubules (Sauro et al, 2007) (Hosaka et al, 2007a) (Elgalaid et al,
2004) (Ciucchi et al, 1995) (Tay et al, 2005) that originally are occupied
by the odontoblastic processes. The water movement is high at the deep
level while diminishes close to the superficial dentin (Pashley et al, 1987)
(Fogel et al, 1988). These differences are related to the variety of diameter
existing between the dentinal tubules of the deep (2.5 µm) and those of the
superficial dentin (0.8 µm) (Pashley et al, 1987) (Pashley, 1991).
Moreover, differences exist between the number of tubules that can be
found in the two areas: 22% at the deep dentin against the 1% of
superficial dentin (Pashley et al, 1987). Some researchers investigated the
water fluid movement present in human being, and considered appropriate
the application of a pulpal pressure of 15-20 mmHg that more likely could
reproduce the clinical situation into the laboratory (Ciucchi et al, 1995)
(Vongsavan and Matthews, 1992). From an adhesive point of view, the
hydration state of dentin can influence the bonding mechanism of selected
resinous materials and limit the durability of the restoration. In particular,
the presence of water can negatively affects those materials containing an
high percentage of hydrophilic monomers (Sauro et al, 2007) (Hosaka et
al, 2007b) (Tay and Pashley, 2003), especially during their initial setting
process (Hiraishi et al, 2008).
In general, it is possible to classify the adhesion mechanism to dentin
into two types: chemical and mechanical-retentive. The chemical adhesion
is realized between the restorative material and the mineral component of
25
dentin, the collagen fibers or its precipitates that are formed after the
acidic pre-treatment (Bowen and Marjenhoff, 1992). The micro-retention
is realized through resin tags formations into the opened dentinal tubules
and the modification of the inter-tubular components (Nakabayashi, 1992)
in a process that should be finalized by the complete polymerization of the
material (Őzok et al, 2004) (Erhardt et al, 2008).
Dentin demineralization causes structural
modifications that
determine an increase of dentinal permeability once the smear layer is
removed and the dentinal tubules are opened (Musanje and Darvell, 2003)
(Balooch et al, 2008). Nowadays, several chemical solutions are intended
to remove the smear layer and to create a direct contact between the
material and the dental substrate (Betolotti, 1992) (Lopes et al, 2003)
(Garberoglio and Bränström, 1976). Acid etching of dentin permits to
remove the peri-tubular dentin, to demineralize the intra-tubular dentin
and to create a rough surface that can establish retention with the
restorative material. Several investigations dealt with the morphological
changes caused by chemical agents, that were based on different
microscopic methodologies (Van Meerbeek et al, 1992) (Urabe et al,
2000) (Balooch et al, 2008) (Lopes et al, 2003) (Van Meerbeek et al,
1993) (Marshall et al, 1993b).
1.7 The use of fiber posts in dentistry
Teeth requiring an endodontic treatment often present an excessive
loss of mineralized tissue, and thus, in comparison to sound teeth, they are
weaker (Trope et al, 1985) (Morgano and Milot, 1993). This consideration
become of great importance in terms of the subsequent prosthetic
26
restoration (Ferrari and Scotti, 2002) (Trabert et al, 1984) (Sorensen et al,
1984). Fiber posts are increasingly assuming importance for the
restoration of endodontically treated teeth with massive coronal
distructions. Different post systems have been proposed over the years,
from the early cast metallic posts to the pre-fabricated metallic posts or the
more recently introduced fiber posts. Fiber reinforced composite posts
(FRC) have been introduced at the beginning of the 90s, as an alternative
to conventional post systems (Duret et al, 1990).(Trabert et al, 1978). In
general, fiber posts consist of unidirectional, pre-tensed fibers, whose
diameter and density strictly influence the quality of the material and its
adhesion process, embedded in a resinous matrix (in particular epoxybased). In particular, differently branded fiber posts are characterized by
differences in their quality, mechanical properties and clinical behaviour
(Grandini et al, 2005) (Ferrari et al, 2007) (Goracci et al, 2008). Fiber
posts present many adavantages, that make their choice in the restoration
of endodontically treated teeth secure and more reliable when compared to
metallic posts. The biomechanical properties of fiber posts have been
reported to be closer to that of dentin, diminishing the incidence of root
fracture that would represent the loss of the tooth (Duret et al, 1990)
(Asmussen et al, 1999) (Malferrari et al, 2004) (Sorrentino et al, 2006) as
fiber posts allow for a better stress distribution compared to cast metal
posts (Ferrari et al, 2000) (Akkayan and Gulmetz 2002) (Heydecke and
Peters, 2002). Their estethical properties could satisfy the growing
patient’s esthetic demands (Martinez-Insua et al, 1998). Different factors
may influence the clinical outcome of a post-restored tooth as post design
(Nissan et al, 2001), length (Okamoto et al, 2008), diameter and root canal
configuration (Morgano et al, 1996) (Innella et al, 2005). Fiber posts are
27
passively retained into root canal. Accordingly, their dislocation resistance
is mostly ascribed to the luting agent and technique adopted for the
cementation (Bitter et al, 2006) (D’Arcangelo et al, 2008). The fiber
post/resin cement combinations have been preferred to conventional luting
agents as they can additionally strengthen the root, and uniformely
distribute stress along the entire root (Dietschi et al, 2008) (Rosenstiel et
al, 1998) (Vichi et al, 2002). The fiber post/resin cement combinations
would allow for an easily ―debonding‖ mode of failure, as it can be solved
by solely repeating the adhesive procedure without compromising the
dental structure (Cagidiaco et al, 2007) (Mannocci et al, 2005).
The choice of the proper luting agent should be based on different
considerations, such as the clinical situation, personal preferences and the
quality of the material. No differences were found in terms of bond
strengths between different resin cements, and Magni et al. recommended
the use of material that would function both as cement and core material
(Magni et al, 2006). This would simplify luting and restorative procedures,
diminishing the number of materials and reducing the interfaces thus
limiting the critical areas prone to be stressed (Magni et al, 2006)
(Mazzitelli et al, 2006). Simplifying luting procedures would be
convenient in terms of time-saving and less-incidence of operator
variability. One-step, self-adhesive resin cements, revealed bond strength
similar to that of well-tried systems, offering new perspectives for the
cementation of fiber posts (Radovic et al, 2008).
The methodology most employed to test the dislocation resistance of
fiber post into root canal is the push-out test. Stresses are created parallel
to the adhesive interfaces (cement/post and cement/dentin) hence better
simulating the clinical situation (Goracci et al, 2007). Microtensile test
28
was also used, but it showed some limitations that made the test less
appropriate for the calculation of the bond strength into root canal
(Goracci et al, 2007) (Goracci et al, 2005). Durability test are necessary to
explore the dental biomaterial behaviour in laboratory in order to be then
clinically recommendable. Thermocycling, cyclic loading and or chewing
simulators are all methods accepted for testing the materials properties and
their long-lasting bonding performances (De Munck et al, 2004).
1.8 Post surface treatments for improving the cement/post bond
Fiber post/cement/dentin complex should form a ―monoblock‖ to
ensure long-lasting restorations (Schwartz and Robbins, 2004). However,
the different properties of the bonding substrates involved make the
monoblock philosophy hard to be achieved (Tay and Pashley, 2007)
(Zicari et al, 2008).
Post surface pre-treatment have been proposed to improve the
retention of the restorative resinous materials to fiber posts (Magni et al,
2007) (Monticelli et al, 2006). According to the nature of the conditioning
process, three main classes can be distinguished: chemical (silane and/or
adhesives application), mechanical (sandblasting or acid etching) and
chemical/mechanical (the combined used of the previous mentioned
mechanisms) (Monticelli et al, 2008a) (Monticelli et al, 2008b). The
adhesion between resin cements and epoxy-resin based fiber posts can
only be realized through the methacrylic group of the cement and the glass
fibers of the posts. As the epoxy matrix completely envelop the glass
fibers, the chemical interaction would result limited. The goal of post
treatments is that of eliminating the superficial incompatible epoxy matrix
29
and to expose the underlying glass fibers that can be then activated by
silanization. Most of these surface treatments create rough surfaces that
should enhance micro-mechanical retentions with the restorative materials
(Magni et al, 2007) (Monticelli et al, 2006) (Le Bell et al, 2004) (Vano et
al, 2006) (Radovic et al, 2007). Silane coupling agents are undoubtedly
the most investigated treatments solutions for fiber post conditionings
(Perdigao et al, 2006) (Goracci et al, 2005). Silane solutions would
enhance the superficial wettability and enable for a stronger chemical
interaction between the two incompatible materials (Lassilla et al, 2004).
As silanes can only promote the adhesion between methacrylic groups and
glass fibers, their use would be improved after pre-treating fiber posts with
additional chemical and/or mechanical procedures (Monticelli et al,
2008b). In the attempt to improve the chemical adhesion between cements
and fiber posts, the combined use of silane/primer have been proposed by
some manufacturers (Monticelli et al, 2008b) (Okuda et al, 2002) (Ferrari
et al, 2002). The rationale of treating fiber post have antecedents on the
procedures previously proposed for dental substrates (Nakabayashi et al,
1991) (Buonocore, 1955). The superficial treatments should create
additional anchoring sites to be bonded and increase the mechanical
retention of resinous materials. Clinicians should take care of the nature of
the treatments, as some of them resulted too aggressive for the integrity of
the fibers, such as, hydrofluoric acid (Vano et al, 2006) and sandblasting
executed with alumina particles with excessive dimensions (Valandro et
al, 2006) (Sahafi et al, 2004). Nowadays, the dental market offers fiber
post already treated with a silicate/silane layer that would ulteriorly
simplify luting procedures (i.e. DT Light SL Post, VDW) with the
convenience of reliable bonds.
30
1.9 An overview of self-adhesive resin cements and their clinical
application
According to literature data, RelyX Unicem was the most
investigated self-adhesive material. Seventy-eight studies reported on the
bonding behaviour and mechanical properties of RelyX Unicem, while 13
investigations dealt with Max-Cem, 7 were related to Multilink Sprint and
5 treated on the bonding ability of G-Cem. Only 2 articles focused on the
bonding performance of Breeze, 5 were concentrated on Bis-Cem, 1 on
Smart-Cem and 1 on I-Cem. Only one study compared the bonding
potential of an experimental self-adhesive cements (Kuraray) to those of
other auto-adhesive materials (Cantoro et al, 2009).
In the most part of the cases, control materials were represented by
well-established total-etch systems (i.e. Variolink and/or Calibra) or selfetch cements (i.e. Panavia). Other comparisons were made with glassionomer cements (in particular Fujy Plus) or compomers (i.e. Dyract).
Only one literature review is available regarding the bonding
effectiveness and mechanism of self-adhesive cements (Radovic et al,
2007), although new reports were then published dealing with new
materials. Due to the differences in their chemical compositions (Han et
al, 2007), comparisons between the cited studies is not always possible,
and dentist should refere to the material itself more than to the class they
belong to. Only 2 clinical studies were conducted to explore the in vivo
performance of a self-adhesive material. One study analyzed the clinical
behaviour of RelyX Unicem used as fiber post luting agent (Naumann et
al, 2007), while the second focused on the bonding ability of RelyX
31
Unicem to lute fixed partial dentures (Behr et al, 2008). Naumann et al.
aimed at determining the survival rate of pre-fabricated rigid titanium post
versus glass fiber post, concluding that the luting agent was appropriate
for both post systems studied (Naumann et al, 2007). Behr et al, compared
the bonding performances of RelyX Unicem and a zinc-phosphate cement
for
luting
fixed
partial
dentures
revealing
comparable
clinical
performances after an observation period of 38 months (Behr et al, 2008).
In both cases, no need for recementation and no failure of the restoration
were evidenced. However, clinical studies are scarce and general
recommendations cannot always be possible. To date, clinicians should
only base on laboratory investigations to drive their conclusions. In vitro
studies are important sources for reproducing, in laboratory, the dental
biomaterials behaviour and characteristics. Bond strength test, microscopic
evaluations (SEM and TEM) and ageing simulations are necessary to
study and foresee a dental materials behaviour. When compared to each
others RelyX Unicem showed superior bond strength than G-Cem for the
cementation of fiber posts (Zicari et al, 2008) and a more regular
adaptation to dentin than Max-Cem and Multilink Sprint (Behr et al, 2009)
with less incidence of post operative allergenic syntoms (Ulker et al,
2009). According to the laboratory data, self-adhesive cements do not
provide effective seal when used on dentin, and a general recommendation
was made to avoid placing the cement in presence of enamel layers (i.e.
veneers, orthodontic brackets) (Vicente et al, 2004) (Duarte et al, 2008)
(Bishara et al, 2005) (Lührs et al, 2009). An increase in the microtensile
bond strength was only obtained after pre-treating enamel with 35%
phosphoric acid (De Munck et al, 2004) (Hikita et al, 2007). That is,
bonding self-adhesive cements to enamel make a previous etching steps
32
imperative. The cement/dentin bond is more complicated, due to the
heterogeneity of the dental substrate. According to the in vitro studies, the
interfacial characteristics between self-adhesive cements and dentin are
formed by scarcely distributed and sporadic resin tag formations, with no
evident hybrid layer both in coronal and in root dentin (Yang et al, 2006)
(Al-Assaf et al, 2007). The bonding process is though to be based on a
chemical interaction between the acidic monomers of the cement and the
minerals of the hydrohiapatite. A second reaction is established between
the acidic monomers and the basic fillers of the cement that generate water
necessary to balance the acid-base chemical reaction. However, pretreating dentin with 35% phosphoric acid did not result in improved bond
strengths of RelyX Unicem. Thus, acid etching dentin was not
recommended during clinical procedures (De Munck et al, 2004) (Hikita
et al, 2007).
Some authors tested the ability of self-adhesive cements to lute
CAD/CAM ceramic restorations. While self-adhesive cements would
show acceptable marginal adaptation in terms of continous margins
(Mormann et al, 2008) (Good et al, 2009), Nuria et al recorded the inferior
microtensile bond strength values of RelyX Unicem when compared to
Panavia F (Nuria et al, 2006). No information can be found regarding the
other self-adhesive cements. Bonding to zirconia ceramic is hampered by
the chemical incompatibility of the restorative material with most of the
cements available (Casucci et al, 2009). Although different zirconia
surface treatments are continuously proposed, Blatz et al found that of the
self-adhesive cements available, those containing adhesive monomers
such as MDP/4-META (i.e. G-Cem) would be adequate to obtain reliable
bonds to zirconia frameworks (Blatz et al, 2009). Senyilmaz et al, found
33
that Max-Cem recorded the inferior shear bond strength when used on pretreated zirconia, concluding that attention should be paid on the chemical
composition of the material adopted (Senyilmaz et al, 2007). Dual curing
self-adhesive cements resulted in superior push-out values when compared
to other resin cements for the cementation of fiber posts (Toman et al,
2009) (Elsayed et al, 2009).
34
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51
Chapter 2
2.1 The interaction between self-adhesive cements and the dentin
substrate
A reliable bond is achieved when an intimate contact is established
between the dental substrate and the material (Moszner et al, 2005). The
dental substrate should be ideally treated to remove the smear layer
created during prosthetic preparations (Nakabayashi et al, 1992)
(Nakabayashi et al, 1991). The material should then infiltrate the opened
spaces, fulfill the voids and polymerized in a short period of time
(Toledano et al, 1999). The hybridization of the dental substrate was
supposed to represent the basis of the bonding mechanism. Several
cements are available on the market for the cementation of indirect
restorations. Resin cements can offer improved mechanical and physical
properties and advanced adhesion mechanisms, thanks to the chemical
interaction they can have with the dental substrates. A classification was
made according to the adhesive systems used (Van Meerbeek et al, 2003).
A discrepancy between the degree of dentin demineralization and depth of
resin penetration has been observed with the cements that utilize the totaletch systems: the voids left at the bottom of the hybrid layer represent
areas prone to premature degradation influencing the long-lasting outcome
of the bonds (Wang and Spencer, 2005) (Spencer et al, 2004). The
simplified version of these bonding agents is represented by the one-bottle
adhesives, in which the acid, the primer and the bonding are accomunate
in a single product. The goal was that of simultaneously demineralize and
infiltrate the adhesive interfaces ideally improving the resin/dentin
interdiffusion zone (Tay and Pashley, 2002). However, the technique
simplification is not always accompanied with superior bond strength
52
values: although the acidic monomers contained into the solution, they
were not strong enough to demineralize the smear layer and subsequently
the dental substrate (Oliveira et al, 2003) (Breschi et al, 2008). The
exposure of weak dentn/adhesive interfaces to the oral cavity would result
in marginal discoloration, poor marginal adaptation and subsequent loss of
retention of the restoration (Mijor and Gordan, 2002) (Mijor et al, 2002)
(Breschi et al, 2008) .
Self-adhesive cements introduced a simple luting approach and the
smear layer is taken as an intermediate bonding substrate. Literature data
report that self-adhesive resin cements only superficially interact with
dentin: interfacial evaluations revealed sporadic and scarcely distributed
resin tags with no hybrid layer formation (Al-Assaf et al, 2007) (AboAmar et al, 2005) (De Munck et al, 2004) (Blatz et al, 2009). Many
investigators focused their attention on microscopic evaluations using
scanning electron microscopy (SEM) and/or transmission electron
microscopy (TEM) to evaluate the adhesive interfaces (Al-Assaf et al,
2007) (De Munck et al, 2004) (Behr et al, 2009). In particular, the only
information still present is related to the bonding ability of RelyX Unicem,
while a clear knowledge of the bonding efficacy and quality of the bond of
others self-adhesive cements is necessary.
The following chapter deals with the observation of adhesive
interfaces established between three classes of resin cements: total-etch,
self-etch and four self-adhesive resin cements. In order to evaluate the
effect of the pre-treatment regime on the demineralization/penetration of
resin into dentin, a morpholocical analysis was performed using the
scanning electron microscopy (SEM) and the Masson’s staining trichrome
technique for light microscopy.
53
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Cabrerizo-Vilchez MA. Effect of acid etching and collagen removal on
dentin wettability and roughness. J Biomed Mater Res 1999; 47: 198-203.
Van Meerbeek B, De Munck J, Yoshida Y, Inoue S, Vargas M,
Vijay P, Van Landuyt K, Lambrechts P, Vanherle G. Buonocore memorial
lecture. Adhesion to enamel and dentin: current status and future
challenges. Oper Dent 2003; 28: 215-235.
Wang Y, Spencer P. Continuing etching of an all-in-one adhesive in
wet dentin tubules. J Dent Res 2005; 84: 350-354.
55
2.2 Limited decalcification/diffusion of self-adhesive cements into
dentin.
Francesca Monticelli, Raquel Osorio, Claudia Mazzitelli, Marco
Ferrari, Manuel Toledano. Journal of Dental Research 2008; 87: 974-979.
Introduction
Resin-based dental luting agents, which are routinely used for luting
gold, composite crowns and all-ceramic restorations have traditionally
required a separate etching step to allow subsequent adhesive infiltration
(Diaz-Arnold et al, 1999). Incomplete adhesive diffusion throughout the
demineralized dentin has been reported for conventional dentin bonding
agents (Spencer and Swafford, 1999). The discrepancy between etching
depth and adhesive penetration led to a large area of exposed collagen at
the interface between the adhesive and prepared dentin surfaces. If this
discrepancy occurs with luting agents that require a separate etching step,
it is conceivable that there may be post-operative sensitivity as a result of
the exposed collagen (Walshaw and Mc Comb, 1996).
To overcome some of the limitations associated with dentin etching,
resin cements that include self-etching primers have been proposed
(Watanabe et al, 1994). This approach has reintroduced the concept of
employing smear layer as bonding substrate, but with novel formulations
that should etch beyond the smear layer into the underlying dentin (Reis et
al, 2005).
A growing interest has been focused on the use of self-adhesive
cements. These systems were designed with the purpose of combining the
favorable characteristics of different cements in a single product. Trying to
satisfy demands for simplification of luting procedures and supposedly
56
leaving little room for application mistakes induced by techniquesensitivity (De Munck et al, 2004) (Ibarra et al, 2007).
Self-adhesive cements do not require any tooth surface pretreatment
and their application is accomplished through a single clinical step,
similarly to more conventional zinc-phosphate and polycarboxylate
cements (Diaz-Arnold et al, 1999).
Based on recent in vitro data, the behavior of the most investigated
self-adhesive cement to dentin (RelyX Unicem) and different restorative
materials should not differ from multi-step resinous cements (Fabianelli et
al, 2005) (Bitter et al, 2006) (Piwowarczyk et al, 2004). However,
concerns emerged regarding the bonding potential of these materials to
enamel and dentin (Behr et al, 2004) (Gerth et al, 2006). Although the
basic adhesion mechanism appears similar for all self-adhesive cements,
these materials are still relatively new and detailed information on their
composition and adhesive properties is limited.
The purpose of this study was to qualitatively compare the
dentin/cement interfacial characteristics of six current commercial
adhesive cements that differ as a function of pre-treatment regimen.
Scanning electron microscopy (SEM) and a staining technique for optical
microscopy, that specifically identifies depth of decalcification/infiltration
or exposed collagen at the dentin/cement interface, were employed. This
study tested the hypothesis that resin cement diffusion into the prepared
dentin surfaces would differ as a function of the pre-treatment regimen.
57
Materials and Methods
Thirty extracted human third molars, stored at 4°C in 0.1% wt/vol
Chloramine T solution were decoronated (Isomet 4000, Buehler, Lake
Bluff, IL) obtaining mid-coronal dentin surfaces that were grinded with
600-grit wet silicon carbide papers creating a uniform thin smear layer.
The use of human specimens was obtained following a protocol that was
approved by the institutional review board (IRB) and with the informed
consent of the donors.
Composite cylinders were made by layering 2 mm-thick increments
of a micro-filled hybrid composite (Gradia Direct Anterior, GC Corp.,
Tokyo, Japan, shade A3) in a split aluminium mold (8 mm diameter/4 mm
height). Each increment was light-cured for 40s (VIP, Bisco Inc.,
Schaumburg, IL, USA, output: 600 mW/cm2). The specimen was removed
from the mold, additionally light-cured from five aspects for 40s each on
the portions previously in contact with the metallic surface of the mold.
The prepared dentin surfaces (n=5 each group) were luted with: 1.
Calibra dual-cured etch-and-rinse cement (Dentsply DeTrey GmbH,
Konstanz, Germany); 2. Panavia F 2.0 dual-cured self-etch cement
(Kuraray Co. Ltd, Osaka, Japan); 3. Multilink Sprint (Ivoclar-Vivadent,
Schaan, Liechtenstein); 4. RelyX Unicem (3M ESPE, St. Paul, MN,
USA); 5. G-Cem (GC Corporation, Tokyo, Japan) 6. Bis-Cem (Bisco,
Schaumburg IL, USA) dual-cured self-adhesive cements.
pH measurements were performed for all tested luting agents. After
mixing, they were dispensed on pH acid indicator strips with narrow
ranges (0.0-1.8; 1.8-3.8; 3.8-5.5; Panreac Química, Barcelona, Spain). The
58
composition, pH and application mode of the tested resin cement systems
are reported in Table 1.
The luting procedure of composite cylinders on dentinal substrates
was performed exerting a constant pressure of 40 g/mm2 during the initial
5-min self-curing period (Goracci et al, 2006).
Table 1. Chemical composition and application mode of the resin cements tested in the study.
Material
Calibra
(H3PO4)
pH= 0.4
Panavia
2.0
pH: 2.4
RelyX
Unicem
pH: 2.1
Multilink
Sprint
pH: 4.2
G-Cem
pH: 2.7
Bis-Cem
pH: 2.1
F
Composition
Application
Caulk 34% Tooth Conditioner Gel (H3PO4)
Prime&Bond NT: acetone, Di- and Tri- methacrylate resins,
Urethane Dimethacrylate, PENTA, Nanofiller- amorphous silicone
dioxide, photoinitiators, stabilizers, cetylamine hydrofluoride.
Calibra: Base: barium boron fluoroalumino silicate glass, bisphenol A, diglydidylmethacrylate, polimerizable dimethacrylate
resin, hydrophobic amorphous fumed silica, titanium dioxide, dicamphoroquinone. Catalyst: barium boron fluoroalumino silicate
glass, bis-phenol A diglydidylmethacrylate, polimerizable
dimethacrylate resin, hydrophobic amorphous fumed silica,
titanium dioxide, benzoyl peroxide.
ED Primer II: Liquid A: 10- methacryloloxydecyl
dihydrogenphosphate; 2-hydroxyethyl methacrylate; N,Ndiethanol-p-toluidine; N-methacryloyl 5-aminosalicylic acid;
water. Liquid B: N,N-diethanol-p-toluidine; Sodium benzen
sulphinate; N-methacryloyl 5-aminosalicylic acid; water.
Panavia F: Paste A: Silanated barium glass; colloidal silica;
Bisphenol A Polyethoxy Dimethacrylate; 10- methacryloloxydecyl
dihydrogenphosphate; Hydrophilic dimethacrylate; Hydrophobic
dimethacrylate; benzoil peroxide; dl-camphoroquinone. Paste B:
Silanated barium glass; Silanated titanium oxide; Sodium fluoride
colloidal silica; Bisphenol A Polyethoxy Dimethacrylate;
Hydrophilic dimethacrylate;Hydrophobic dimethacrylate; N,Ndiethanol-p-toluidine; Sodium 2,4,6-Triisopropyl benzene sulfinate
Powder: glass fillers, silica, calcium hydroxide, self-curing
initiators, pigments, light-curing initiators. Liquid: methacrylated
phosphoric esters, dimethacrylates, acetate, stabilizers, self-curing
initiators, light-curing initiators.
Dimethacrylates; adhesive monomer; Fillers;
initiators /
stabilizers.
Apply etchant (30s).
Water rinse (20s). Airdrying. Apply
adhesive in a single
coat. Gently air-drying
after 5s. Light-cure for
20s. Mix base and
catalyst (1:1). Apply
and self-cure (5 min).
Light-cure (40s).
UDMA; phosphoric acid ester monomer; 4-META; water;
dimethacrylates; silica powder;
initiators/stabilizers; fluoro-amino-silicate glass.
Bis (Hydroxyethyl methacrylate) phosphate (Base); Tetraethylene
glycol dimethacrylate; dental glass.
Mix ED Primer A+B
(1:1). Apply on the
tooth. Gently air-blow
after 30s. Mix Paste
A+B (1:1) for 20 s.
Apply and self-cure (5
min) Light-cure (40s)
Mix cement. Apply,
self-cure (5 min) and
light-cure (40s)
Mix cement. Apply,
self-cure (5 min) and
light-cure (40s)
Mix cement. Apply,
self-cure (5 min) and
light-cure (40s).
Mix cement. Apply,
self-cure (5 min) and
light-cure (40s)
59
Trichromic stain and microscopic observation
After 24h storage (37°C at 100% humidity), three samples from each
group were sectioned perpendicularly to the bonded surface into 1-mm
thick slabs using a water-cooled, low-speed diamond saw (Isomet 4000).
A total of 12 sections were analyzed for each dentin treatment. Slabs were
glued on methacrylate supports with photo-curing adhesive (Technovit
7200 VLC, Kulzer, Norderstedt, Germany) and grinded with an Exakt
polishing machine (EXAKT Technologies, Inc., Oklahoma City, OK,
USA) using SiC abrasive wet papers (800; 1200; 2500; 4000 grit) until
getting a thickness of 5-6µm. Differential staining was accomplished with
Masson’s trichrome, a classic bone stain (Erhardt et al, 2008). After coverslipping with mounting media, they were examined using a light
microscope (BH2, Olympus, Tokyo, Japan) at 100x magnification.
Scanning Electron Microscopy
Two additional specimens for each group were prepared for SEM
evaluation. Samples were sectioned perpendicularly to the bonded surface
(Isomet 4000). Each section was polished with wet abrasive SiC papers,
gently decalcified (37% phosphoric acid/10s) and deproteinized (2%
NaOCl solution/1 min) ultrasonicated in 96% ethanol for 2 min and airdried. Samples were mounted in stubs, sputter-coated with gold (Polaron
Range SC7620; Quorum Technology, Newhaven, UK) and observed
under a scanning electron microscope (SEM; JSM-6060 LV, JEOL,
Tokyo, Japan) at different magnifications to evaluate for resin tags and
hybrid layer formation. Impressions of the restored teeth and positive
60
impression replicas were fabricated (Chersoni et al, 2004) and observed by
SEM to control for artefact formation.
Results
According to the Masson’s trichrome-staining technique, the
mineralized dentin stains green, whereas the resin cement is clear with
filler particles. The staining reaction of proteins is non-specific and some
non-collagenous proteins may have been marked. Type I collagen
represents the 90% of dentin organic matrix. Thus, it is likely that the
protein staining (red) resulted from dentin collagen unprotected by mineral
and/or resin.
Using the conventional etch & rinse luting agent (Calibra) a distinct
red zone of denuded collagen at the basis of the bonded interface was
observed. Tubules were opened (Fig. 1A), and hybrid layer with resin tags
formation were identified by SEM (Fig. 2 A). At the dentin/cement
interface of teeth luted with the self-etching cement (Panavia) a narrow
purple line representing mild collagen demineralization is detectable at the
intact dentin surface (Figs. 1B). After Multilink Sprint application, dentin
surface appeared in red (decalcified), but not resin infiltrated (Fig. 1C).
No demineralization/infiltration of dentin was evident for the selfadhesive cements Rely X Unicem (Fig. 1D), G-Cem (Fig. 1E) or Bis-Cem
(Fig. 1F), that produced similar interfacial patterns. All light microscopy
sections from Bis-Cem group debonded at the cement/dentin interfacial
level during laboratory preparation procedures (Fig. 1F).
A scanning electron micrograph of a Bis-Cem bonded to dentin
revealed an intimate adaptation with the substrate. However, no signs of
hybrid layer formation with the underlying dentin could be noticed; no
61
resin tags were observed (Fig. 2 B). All the tested auto-adhesive luting
cements recorded an acidic pH ranging from 2.1 and 4.2 after mixing
(Table 1).
62
Figure 1. Representative light micrographs of cement/dentin interfaces
stained with Masson’s trichrome: mineralized dentin (green), resin cement
(clear with filler particles), exposed protein (red). A. A distinct red zone of
exposed protein was identified in the sections recovered from specimens
etched with phosphoric acid (Calibra). B-C. A slight purple line
representing collagen partially reacted with resin cement is detectable at
the interface between dentin and the self-etching primer (B; Panavia F 2.0)
or Multilink Sprint (C). D-E-F. No signs of demineralization and/or
exposed protein (red stain) are detectable at the cement/dentin interface of
Rely X Unicem (D), G-Cem (E) and Bis-Cem (F). (Original magnification
100x, bar 10 m).
A
B
C
D
F
63
Figure 2: Scanning electron micrograpfs of G-Cem (A); RelyX Unicem
(B), Multilink Sprint (C), Calibra (D), Panavia F 2.0 (E) and Bis-Cem (F).
When using the multi-step resin cement (Calibra), dentin was
demineralized and consecutively infiltrated by resin. Resin tags and resin
cement/hybrid zone are identified. When luting with self-adhesive
cements, tubules were not infiltrated by resin, but intimate adaptation is
patent, no distinct morphological manifestation of interaction with dentin
may be observed.
A
B
C
D
E
F
64
Discussion
Within the limitations of this study, the combined application of
trichromic technique and SEM examination provided information about
the demineralized dentin depth, extent of adhesive diffusion and hybrid
layer formation (Spencer and Swafford, 1999). Differences in resin cement
diffusion into the prepared dentin surfaces as a function of the pretreatment regimen were evidenced. The interfacial pattern of the tested
simplified self-adhesive cements was not comparable to that of
conventional resin-based systems. Thus, the null hypothesis has to be
rejected.
The substantial zone of demineralization produced by the etch-andrinse pre-treatment facilitates resin penetration, but infiltration of
Prime&Bond NT was not complete, as it was encountered when compared
to other etch&rinse systems (Spencer et al, 2004). It seems that the solvent
(acetone) is not able to generate interfibrillar spaces wide enough to
accommodate the infiltrating adhesive (Pashley et al, 2002). This adhesive
does not contain monomers capable of enhancing diffusion and lowering
the initial viscosity of the mixture (HEMA or TEGDMA) (Toledano et al,
2006).
Differing from the application of the etch & rinse system, the mild
etching-priming blend (Panavia; pH=2.4) produced minimal dentin
demineralization, but resin penetration is identified. It contains ambiphilic
monomers (HEMA, 10-MDP, 5-NMSA), with low molecular weight, that
may have selectively diffused into dentin (Al-Assaf et al, 2006), forming
the hybridized complex (Walker et al, 2002) (Reis et al, 2005).
65
Similarly to self-etching primer formulations, self-adhesive cements
contain multifunctional phosphoric acid methacrylates that are claimed to
react with the hydroxyapatite of the hard tooth tissue (Moszner et al, 2005)
(Fu et al, 2005) (Hikita et al, 2007). However, no evidences of
decalcification/infiltration into dentin are found in any of the tested selfadhesive cements. To achieve a correct infiltration pattern, these cements
should be able to etch the substrate in a relatively short time, requiring
optimal wetting properties to ensure a fast interaction with dental hard
tissues (Moszner et al, 2005). Ideally, the thin smear layer evaluated in
this study should allow acidic monomers to freely reach the mineralized
tissue underneath (Reis et al, 2005), but it did not occur. Despite of the
initial acidic pH, Rely X Unicem and Bis-Cem did not produce any
evidence of dentin demineralization and/or hybridization in a micrometer
scale (Al-Assaf et al, 2004) (Yang et al, 2006). The adhesive joint
appeared essentially similar to that of some conventional luting agents
(silicate cements or zinc-phosphate) (Beher et al, 2004).
Some reasons may be advocated regarding the limited capacity of
these cements to effectively diffuse up and decalcify the underlying
dentin: 1) high viscosity (De Munck et al, 2004), that may rapidly increase
as an acid-base reaction (ionic bond formation and setting), that is
reminiscent of conventional cements (i.e. silicate or glass-ionomers), is
supposed to occur (Fukuda et al, 2003); 2) a neutralization effect during
setting, as these chemical reactions involve water releasing and alkaline
filler that may raise the pH level (Behr et al, 2004) (Al-Assaf et al, 2006);
this neutralization effect may also be exerted by dentin buffering
components contained in the smear layer (Reis et al, 2005) (Olivera et al,
2003).
66
In the attempt of improving diffusivity, a reduction in the initial pH
of the cement formulations may be proposed, but it would impair the
hydrolytic stability of acidic methacrylates phosphates (Moszner et al,
2005), may reduce polymerization efficacy (Nunes et al; 2006) and should
leave an unprotected interface prone to degradation.
The presence of smear layer has been recognized as the ―weak‖ link
in bonding of glass ionomers to dentin, and may also be the case of selfadhesive cements (Al- Assaf et al, 2004). Phosphoric acid etching, prior to
the application of the self-adhesive cement, has been shown to be
detrimental for effective dentin bonding (De Munck et al, 2004). Most
likely, the choice of milder acidic agents to remove the superficial loosely
bound fraction of smear layer could somewhat enhance adhesion.
In the case of G-Cem, a self-adhering capacity to dentin may be
supposed due to the incorporation of 4-META that bonds by a chelating
reaction to calcium ions in apatite (Abo et al, 2004). Water in the cement
composition is expected to help the conditioning reaction, reducing the
time needed for interacting with the substrate. However, the relatively
weak bonding potential and the high molecular weight of the functional
monomer are expected to poorly contribute to the supposed chemical
reaction, within a clinically reasonable time (Yoshida et al, 2004).
The light discrepancy between demineralization and infiltration
depths recorded for Multilink Sprint may be the result of a deeper
diffusion of non-cured non-neutralized acidic monomers below the smear
layer. Similarly to self-etching primers, these residuals may retain their
etching potential forming an unprotected dentin zone and jeopardizing
adhesion (Wang and Spencer 2005) (Carvalho et al, 2005).
67
A bond strength study performed under same laboratory conditions
(Mazzitelli et al, 2008), attained results that correlate with present
findings. Calibra obtained the highest bond strength and Bis-Cem the
lowest (68% of Bis-Cem specimens produced pre-testing failures); Rely-X
and G-Cem recorded bond strengths somewhat higher than Multilink
Sprint and Bis-Cem, but due to the high standard deviations, differences
were not encountered. Long-term bond strength results remain to be
ascertained.
Intimate adaptation of self-adhesive cements to dentin was observed
by SEM, but no hybrid layer or resin tags formation were evidenced.
Other mechanisms (as chemical interactions) had been advocated to occur
at these complex interfaces (De Munck et al, 2004) (Hikita et al, 2007). It
should also be noticed, that decalcification (red line) of underlying dentin
was not produced by any of these cements, so ionic bonding may also be
impaired.
Following
the
adhesion/decalcification
concept,
demineralization is a surface-controlled phenomena involving interaction
with hydroxyapatite and depends upon adsorption of the acid anions onto
hydroxyapatite. Acidity of the cements/adhesives may not be as
determining as previously been thought (Yoshida et al, 2001).
It is worth mentioning that a standardized cementation pressure was
applied in this experiment in consideration of previous investigations
(Goracci et al, 2006). The cement viscosity most likely decreased while
undergoing shear, producing better adaptation and reducing cement film
thickness. However, such a thixotropic behavior does not necessarily
allow a deeper interaction of auto-adhesive cements with the substrate (De
Munck et al, 2004).
68
In conclusion, self-adhesive cements were not able to completely
demineralise/dissolve the smear layer and no decalcification/infiltration of
dentin was observed. The presence of partially demineralized/infiltrated
smear layer and/or micromechanical retention with dentin may be
responsible for the previously reported adhesion values, always weaker
than those of conventional resin-based cements (De Munck et al, 2004)
(Mazzitelli et al, 2008).
69
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73
Chapter 3
3.1 Vital dentin as adhesive substrate
Vital dentin is characterized by an outward fluid flow through
dentinal tubules. According to the hydrodynamic theory, the rapid fluid
movements would activate the pulpal nerves and cause dentine sensitivity
(Pashley, 1994). In order to limit this inconvenience, the resinous material
should fulfill the tubules and prevent dentine sensitivity. From the other
side, there is a common opinion for which the water proceeding through
the dentinal tubules may reach the bonded interface and permeate through
the material before the advent of the complete polymerization (Itthagarun
et al, 2004) (Carrilho et al, 2007). This phenomena is particularly evident
in contemporary adhesive systems, whose formulations are based on an
high amount of hydrophilic monomers (Yiu et al, 2006). Once they absorb
water, they undergo a plasticization effect that affect their mechanical
properties (Ito et al, 2005) (Sideridou et al, 2003) (Yiu et al, 2004). In this
case, the longevity of the restoration is jeopardize, and microleakage and
post-operative sensitivity is more likely to be observed.
The water transudation occurring in vivo conditions should be taken
into consideration when simulating the dental biomaterials behaviour in
laboratory. Prosthetic preparation does not always require previous
endodontic treatments, that is vital dentin would represent the bonding
substrate of interest. The convective water fluid flow can be easily
reproduced in laboratory allowing for a better simulation of intra-oral
conditions. In the following investigation, the effects of a pulpal pressure
of 15 cm H2O on the bonding performance of different self-adhesive
cements and a cement based on a total-etch system were evaluated. The
74
microtensile test was used to measure the bond strength in presence or not
of a simulated pulpal pressure; representative fractured slices were used
for the SEM evaluations.
75
References
Carrilho MR, Tay FR, Sword J, Donnelly AM, Agee KA, Nishitani
Y, Sadek FT, Carvalho RM, Pashley DH. Dentine sealing provided by
smear layer/smear plugs vs. adhesive resins/resin tags. Eur J Oral Sci
2007; 115: 321-329.
Ito S, Hashimoto M, Wadgaonkar B, Svizero N, Carvalho RM, Yiu
C, Rueggeberg FA, Foulger S, Saito T, Nishitani Y, Yoshiyama M, Tay
FR, Pashley DH. Effects of resin hydrophilicity on water sorption and
changes in modulus of elasticity. Biomaterials 2005; 26: 6449-6459.
Itthagarun A, Tay FR, Pashley DH, Wefel JS, Garcia-Godoy F, Wei
SHY. Single step, self-etch adhesives behave as permeable membranes
after polymerization. Part III. Evidence from fluid conductance and
artificial caries inhibition. Am J Dent 2004; 17: 394-400.
Pashley DH. Dentine permeability and its role in the pathobiology of
dentine sensitivity. Arch Oral Biol 1994; 39: 73-80.
Sideridou I, Tserki V, Papanastasiou G. Study of water sorption,
solubility and modulus of elasticity of light-cured dimethacrylate-based
dental resins. Biomaterials 2003; 24: 655.665.
Yiu CK, Hiraishi N, Chersoni S, Breschi L, Ferrari M, Prati C, King
NM, Pashley DH, Tay FR. Single bottle adhesive behave as permeable
membranes after polymerization. Part II. Differential permeability
reduction with an oxalate desensitizer. J Dent 2006; 34: 106-116.
Yiu CK, King NM, Pashley DH, Suh BI, Carvalho RM, Carrilho
MR, Tay FR. Effects of resin hydrophilicity and water storage on resin
strength. Biomaterials 2004; 25: 5789-5796.
76
3.2 Effect of simulated pulpal pressure on self-adhesive cements
bonding to dentin.
Claudia Mazzitelli, Francesca Monticelli, Raquel Osorio, Alessio Casucci,
Manuel Toledano, Marco Ferrari. Dental Materials 2008; 24: 1156-1163.
Introduction
Successful bonding of luting agents to tooth structure is imperative
for retention and marginal adaptation of indirect tooth-colored restorations
(Abo-Hamar et al, 2005). Prosthetic preparations often require the removal
of a large amount of enamel resulting in exposed dentin surfaces. Vital
dentin is hydrated and characterized by an outward fluid flow from
dentinal tubules (Elgalaid et al, 2004) (Sauro et al, 2007) (Hosaka et al,
2007a).
Adverse chemical interactions and adhesive permeability were
identified as the two main factors responsible for the reduction in bond
strength when auto/dual-cured slow setting resin cements were coupled to
bonding on hydrated dentin (Tay et al, 2003). The trans-dentinal fluid
movement under a slight positive pulpal pressure may permeate
polymerized adhesive interfaces and hinder with the subsequent coupling
of the cement (Sauro et al, 2007).
Conventional resin cements that rely on the application of etch-andrinse adhesives are mostly affected by simulated pulpal pressure, due to
the increase in dentin permeability after etching (Musanje et al, 2003).
Large fluid shifts during bonding may permit water from dentin to mix
with the hydrophilic monomers during solvent evaporation, plasticizing
polymer chains and promoting hydrolysis of resin and collagen fibrillar
77
components (Sauro et al, 2007) (Musanje et al, 2003) (Ito et al, 2005)
(Hashimoto et al, 2003) (Yiu et al, 2006) Hashimoto et al, 2004).
Self-etch luting systems do not require separate conditioning of
dentin, since their adhesion mechanism is based on the partial retention of
smear layer. Although this feature should render them less affected by
moisture contamination, degradation of resin-dentin bonds may also be
expected to occur also in self-etch systems, due to the presence of
hydrophilic monomers and high solvent concentrations in the adhesive
blends (Hashimoto et al, 2004) (Okuda et al, 2002).
Simplified self-adhesive cements have been marketed to simplify
clinical procedures and overcome the technique sensitivity of multi-step
systems. These luting agents do not require any pretreatment of the tooth
surface and their application is accomplished through a single clinical step.
The adhesive mechanism is claimed to rely on the chemical reaction
between phosphoric acid monomers and hydroxyapatite of dental hard
tissues (Pashley et al, 1999) (De Munck et al, 2004). Their application on
smear layer-covered substrates should limit post-operative sensitivity and
ideally, make these materials less affected to moisture.
Alternative strategies have been recently proposed in an attempt to
limit water-induced interfacial changes, such as the application of static
seating pressure during luting or an additional layer of hydrophobic resin
(Chieffi et al, 2007) (Goracci et al, 2006). However, the real benefit of
these procedures under simulated pulpal pressure is uncertain.
Therefore, the aim of this study was to determine the bond strength
of different self-adhesive cements to deep-coronal dentin with and without
simulated pulpal pressure. The null hypotheses tested are that is that there
78
is no difference in the bond strength of different adhesive cements to
dentin regardless of the presence or absence of simulated pulpal pressure.
Materials and Methods
Experimental design
Thirty human caries-free third molars stored in 0.5% Chloramine T
solution at 4°C were cut above the CEJ to expose flat deep-coronal dentin
surfaces. The root of each tooth was cut below the CEJ with a slow speed
diamond saw (Isomet, Buehler Ltd, Lake Bluff, IL, USA) under watercooling so as to expose the pulp chamber. The pulp tissue was completely
removed with forceps, trying not to touch the pulp chamber walls.
Composite cylinders were made by layering two 2-mm thick
increments of a nano-filled hybrid light cured composite (Aelite AllPurpose Body, Bisco, Schaumburg, IL, USA, shade A3, Batch no.
0500002459) in a split aluminium mold ( 8 mm; height: 4 mm). Each
increment was light-cured for 40 s with a halogen-curing light Astralis 7
(Ivoclar Vivadent, Schaan, Liechtenstein). Light output was monitored at
600 mW/cm2. Specimens were removed from the mold, and additionally
light-cured from five aspects for 40 s each on the portion previously in
contact with the metal surface of the mold.
Resin blocks were abraded with #600 SiC-paper under water-cooling
in order to simulate the clinical condition of sandblasting. Before bonding,
each cylinder was cleaned with 34% phosphoric acid (Scotchbond
Etchant, 3M ESPE, Seefeld, Germany) for 30 s, rinsed with deionised
water for 20 s and air-dried.
79
Luting procedures
Half of the specimens (n=15) were glued with cyanoacrylate (Super
Attak Gel, Henkel Loctite Adesivi, s.r.l. Milan, Italy) to a Plexiglass slab
(1.5 x 1.5 x 0.5 cm), taking care that the pulp chamber resulted completely
glue-free. On one side of each Plexiglass plate a fissure was created with a
diamond bur and a short length of 18-gauge stainless steel tube was glued
parallel to the platform extending 2 cm out from the platform (Ciucchi et
al, 1995). Each slab-tooth assembly was connected to a 20 mL syringe
barrel through polyethylene tubing. All syringe barrels were filled with
deionised water to produce a simulated hydrostatic pulpal pressure of 15
cm of H2O at the dentin surface. Dentin was ground with #600 SiC-paper
in order to create a thin smear layer. Then, the surface was etched with
34% ortho-phosphoric acid for 15 s and thoroughly rinsed with water.
After
assessing
the
presence
of
fluid
transudation
under
a
stereomicroscope at 40x to confirm the permeability of the dentin, before
luting, the smear layer was re-created by means of a new grinding
procedure (600 grit).
Five different luting materials were used: 1) Calibra (DeTrey
Dentsply, Konstanz, Germany); 2) Multilink Sprint (Ivoclar Vivadent,
Schaan, Liechtenstein); 3) BisCem (Bisco, Schaumburg, IL, USA); 4) GCEM (GC corp., Tokyo, Japan); 5 RelyX Unicem (3M ESPE, Seefeld,
Germany).
All the materials were handled strictly following manufacturer’s
recommendations, at room temperature (RT: 23.0°C ± 1.0°C) and relative
humidity (50% ± 5%). Application mode, chemical composition and pH
values of the investigated materials are reported in Table 1.
80
When Calibra was used for luting, a silane solution (Calibra Silane
Coupling Agent, DeTrey Dentsply) was applied to the composite surface
to be bonded and spread with air blowing.
The luting procedure was performed under a constant pressure of 1
kg (0.098 MPa) by means of a metal tool at RT until the seating of the
material was complete. The seating force was applied for the first 5
minutes leaving the material to set in the self-curing mode. Finally, after 5
min of self-curing, two additional 20 s of light irradiations (Astralis 7)
were performed from each side of the specimens to ensure optimal
polymerization.
Bonded specimens were stored in a laboratory incubator for one
month at 37°C and 100% relative humidity until the microtensile bond
strength test was performed. In the case of group 1, the simulated
hydrostatic pulpal pressure was maintained until testing.
Microtensile bond strength test
Teeth were sectioned vertically into 1 mm-thick slabs with a slowspeed diamond saw (Isomet). Each slab was fixed on a glass platform with
sticky wax and serially sectioned into 1 mm2 sticks, according to the ―nontrimming‖ method of the microtensile test. Each stick was measured with
a digital caliper (Orteam s.r.l, Milan, Italy), glued with cyanoacrylate
(Super Attak Gel) to the free-sliding doors of a Gerardeli’s jig and tested
in a universal testing machine (Triax Digital 50, Controls, Milan, Italy;
cross-head speed: 0.5 mm/min) until failure.
Failure modes were evaluated by a single operator under a
stereomicroscope (Olympus SZ-CTV, Olympus, Tokyo, Japan) at 40x
magnification and classified as cohesive (within the cement, dentin or
81
composite), adhesive (between composite/cement or at the cement/dentin
level) or mixed.
Statistical analysis
Bond strength data were first analyzed for normality with the
Kolmogorov-Smirnov test and the Levene’s test for equal variance. All the
sticks that failed prematurely were included and considered in the
statistical calculations as ―zero bond‖ values. As bond strength data were
not normally distributed, Kruskall-Wallis Analysis of Variance was
applied to assess differences in bond strength among the experimental
groups (p<0.05). Mann-Whitney tests were used for post-hoc comparisons
(p <0.001).
Scanning Electron Microscopy evaluation (SEM)
Four fractured sticks from each experimental subgroup (previously
classified as adhesive or mixed failures) were dehydrated with ascending
ethanol solutions, mounted on metal stubs, gold-sputtered (Polaron Range
SC 7620, Quorum Technology, Newhaven, UK) and evaluated under a
Scanning Electron Microscope (SEM, JSM-6060LV, Jeol, Tokyo, Japan)
at different magnification.
82
83
Results
Microtensile bond strength test
Mean microtensile bond strength values recorded in the groups
tested are summarized in Table 2. Bond strengths were statistically
influenced by the presence of simulated pulpal pressure (p<0.001) and by
the type of luting agent (p<0.05).
When no pulpal pressure was applied, the total-etch cement system
Calibra exhibited the highest luting strength. RelyX Unicem and G-Cem
produced significantly lower bond strengths, while Bis-Cem recorded the
lowest µTBS under the same laboratory condition. In the presence of
simulated pulpal pressure, bond strength values of Calibra significantly
decreased. . The self-adhesive cements RelyX Unicem and Bis-Cem gave
significant increased in bond strength. The bonding effectiveness of the
self-adhesive cements Multilink Sprint and G-Cem were not influenced by
the experimental conditions, since no significant differences were found in
the presence or absence of simulated pulpal pressure (p>0.05).
The percentage of failure mode distribution is summarized in Table
2. Specimens bonded with self-adhesive cements (Multilink Sprint, Rely X
Unicem, G-Cem and Bis-Cem) recorded a higher percentage of cohesive
failures within the cement layer under simulated pulpal pressure than
when no pulpal pressure was applied. Higher percentages of adhesive
failures were related to lower bond strengths. Adhesive failures occurred
mainly at the cement/dentin interface. A remarkable percentage of pre-test
failures (34-74%, Table 2) were recorded in all the experimental groups.
84
Pulpal Pressure
No Pulpal Pressure
Failure Mode
Experimental groups
Failure Mode
Mean (SD)
PF
C
A
M
Multilink Sprint
74%
40%
40%
20%
Rely X Unicem
23%
37%
36%
Calibra
41%
48%
G-Cem
48%
Bis-Cem
34%
Mean (SD)
PF
C
A
M
2.3 (4.4) A
59%
20%
60%
20%
4.5 (6.4) a
27%
16.5 (12.5) B
34%
28%
54%
18%
11.4 (10.1) b*
20%
32%
12.0 (11.7) BC
21%
28%
55%
17%
20.8 (13.5) c*
43%
40%
17%
8.8 (9.0) C
37%
42%
54%
4%
10.5 (11.1) ab
33%
50%
17%
12.4 (11.2) BC
68%
29%
57%
14%
2.4 (3.9) a*
Table 2: Mean bond strength (SD) values (MPa) and failure mode distribution (%) recorded in each experimental group.
PF: premature failure; C: cohesive (within the cement, dentin or composite); A: adhesibe (between the composite and the cement
or at the cement/dentin level); M: mixed. Different letters in each column and asterisks in each row indicates significant
differences (p<0.001).
85
Scanning electron microscopy analysis (SEM)
SEM images of debonded beams are shown in Figs. 1-2 (with and
without PP, respectively).
When RelyX Unicem was used, structural defects were observed in
fractured specimens tested under pulpal pressure (Fig. 1A). These defects
consisted of compartmentalized honeycombs and resin globules (Fig. 2)
and were absent when no pulpal pressure was applied (Fig. 1B).
Under simulated pulpal pressure, debonded specimens of Bis-Cem
were characterized by the presence of dentinal tubules occluded by resin
tags (Fig. 1C). The occurrence of globular interfacial agglomerates was
assessed when using the cement without PP (Fig. 1D) (Fig. 3).
Multilink Sprint interacted with the underlying dentin forming short
resin tags that were detected both in the presence or absence of PP (Figs
1E and F).
Under pulpal perfusion, a detachment of filler from the resinous
matrix was noticedwhen luting woth G-Cem (Fig. 1G). This feature was
not evident in the absence of pulpal pressure (Fig. 1H).
Irregular adhesive interfaces were evident for the total-etch system
Calibra under trans-dentinal perfusion (Fig. 1I). When luting procedures
were performed in the absence of pulpal pressure, demineralised/infiltrated
areas with resin tags formation were detectable (Fig. 1J).
86
87
Fig 1. SEM microphotographs of representative fractured beams bonded
respectively with or without PP: A and B) RelyX Unicem; C and D) Bis-Cem; E and F)
Multilink Sprint; G and H) G-Cem; I and J) Calibra. Trans-dentinal perfusion somewhat
affected the extent of polymerization of RelyX Unicem and Calibra (A and I): areas of
compartimentalized honeycomb structures and resin globules are detectable at the
interface level. Light demineralization with the formation of resin tags in The tubule
orifices is evident in the case of Bis-Cem and Multilink Sprint (C and E). The authors do
not know how short or long the tags are from this projecton. The application of simulated
pulpal pressure impaired G-Cem cohesive strength: frank detachments between the
resinous matrix and the filler are evident in the cement bulk (G). In the absence of PP, no
signs of interaction with dentin are evident for RelyX Unicem and G-Cem. Multilink
Sprint showed a lower demineralising ability and infiltration of dentinal tubules (B and
H). Lmited areas of poor polymerization are detectable in the Bis-Cem group (D).
Tubules filled with adhesive/cement residues are visible when Calibra was applied (J).
88
Fig. 2: High magnification SEM image of a debonded beam luted with
RelyX Unicem under PP (1.500x). The fractured surface consisted of porous
agglomerate and honeycomb structures, probably filled with water coming from
the perfused dentin that made the cement/dentin interface irregular.
Fig. 3: SEM image of a debonded beam luted with Bis-Cem when no
pulpal pressure was applied (400x, bar 50 um). The fracture pattern showed a
rough, irregular interface. These sites may expedite restoration debonding.
89
Discussion
The hydration of dentin surfaces represents a critical variable during
bonding procedures, especially when testing adhesive materials in vitro
with the intent of simulating in vivo conditions (Sauro et al, 2007).
The results of this investigation require the rejection of the null
hypotheses, since microtensile bond strength was affected by the presence
of simulated pulpal pressure and the bonding cement.
Deep vital dentin is a highly permeable substrate in which
hydrodynamic outward fluid may occur along dentinal tubules (Gale and
Darvell, 1999). The presence of smear layer and smear plugs in dentinal
tubules limits excessive transudation (Grégoire et al, 2003) (Őzok et al,
2004). To achieve optimal dentinal sealing, resin monomers should flow
into tubule orifices, which are water-filled, diffuse into the interfibrillar
collagen spaces and properly polymerize forming hybridized resin tags
(Őzok et al, 2004).
Nevertheless, dentin wetness and fluid movement through bonded
interfaces may hinder optimal resin seal (Tay and Pahley, 2003) (Tay et al,
2004). In the absence of pulpal pressure, the bond strength of the tested
etch-and-rinse luting system (Calibra) was significantly higher to that
recorded on perfused dentin. The increased trans-dentinal permeability
after smear layer removal may have counteracted adhesive penetration and
exerted an inhibitory effect on polymerization.
The omission of HEMA in in Prime&Bond NT has been considered
advantageous in removing water, separating it from other components
upon solvent evaporation (Van Meerbeek et al, 2005). The acetone
contained in the adhesive blend is extremely volatile (Glaucher et al,
90
2003) and its rapid evaporation facilitate the formation of a monomer-rich
phase, which may promote cross-linking (Yip and McHugh, 2005).
However, excessive transudation of fluids from dentinal tubules and
substrate moisture may exceed its water-chasing ability: with acetone
evaporation exceeding that of water, the accumulation of the aqueous
fraction accumulated in the adhesive film prior to polymerization tends to
impaire bonding (Zhou et al, 2001).
As self-adhesive cements are applied on smear layer-covered dentin,
simulated pulpal pressure should not significantly affect their behaviour.
Nevertheless, the simplified luting systems tested recorded differences in
their tolerance to wetness and adhesive effectiveness. Manufacturers do
not provide detailed information on the chemical composition of these
cements. However, the adhesion mechanism of some self-adhesive
cements seems closer to the behaviour of conventional luting systems (i.e.
silicate or zinc phosphate cements).
Rely X Unicem and Bis-Cem achieved higher bond strengths under
simulated dentin perfusion than in the absence of PP revealing a setting
acid-base reaction close to that of silicate cements. In the presence of
water, silicate cement setting may occur due to the reaction between
phosphoric acid and glass silicate fillers (Anusavice, 2003). Theoretically,
the phosphoric acid esters of self-adhesive cements behave similarly and
need water to become ionized and acid-etch and interact with dentin
(Moszner et al, 2005). Since water is not mentioned in their chemical
composition and may only derive from the interaction of phosphoric acid
groups and alkaline fillers or tooth apatite, intrinsic dentinal wetness may
have optimized these acid-base reactions allowing better setting. However,
concerns remain regarding the ability of these high viscosity materials to
91
etch through clinically relevant smear layers into the underlying dentin
(Behr et al, 2004) (Gerth et al, 2006).
Despite the improvement in bond strength, RelyX Unicem produced
areas of irregular adhesive interfaces under pulpal pressure. The
observation of material discontinuity (presence of globules), ―honeycomb
structures‖ (Fig. 3) on the fractured dentinal side of the specimens may
represent a separation of phase of resin components and has been
identified in previous studies that employed self-etch or etch-and-rinse
adhesives (Mack et al, 2002) (Tay et al, 2002). In those studies, the
authors suggested that the honeycomb structures were filled with water
that permeated from dentinal tubules or represented incompletely
polymerized regions due to water entrapment. Globules may be the result
of the emulsion of resin cement hydrophobic components once in contact
with water (Tay and Pashley, 2003) (Carvalho et al, 2004). When stressed
to failure, these abundant defects may act as stress raisers that expedite
crack propagation through the resin cement bulk (Fig. 3). The higher
number of cohesive failures that occurred among the experimental groups
when luted under simulated intrapulpal pressure may be related to the
excessive water sorption of the material (Hosaka et al, 2007b) (Tay et al,
2005), especially when compared to the control group, in which the
adhesive failures at the cement/dentin interface were prevalent.
The absence of pulpal pressure (i.e. dentin perfusion) limited the
auto-adhesive cement bonding potential, especially for Bis-Cem.
The presence of water in the chemical composition of G-Cem may
explain the similar behaviour exerted by the cement both on moist and
perfused dentin. The bonding potential of the functional acidic monomer
(4-META) and its high molecular weight, may have contributed to the
92
chemical reaction with dentin, in both the tested experimental conditions
(Abo et al, 2006) (Yoshida et al, 2004).
The patent tubule orifices detected on dentinal substrates bonded
with Multilink Sprint in the absence of pulpal pressure, may depend on the
slight diffusion of low molecular weight acidic monomers from the high
viscosity cement bulk through the smear layer (Fig. 1C). This appearance
was more evident on perfused dentin where the cement exerted a superior
etching potential most likely due to acidic monomers dilution (Fig. 2C).
However, deeper interaction with dentin did not always reflect a superior
bonding potential. If not properly neutralized, these monomers may retain
their etching potential
affecting the polymerizing reaction
and
jeopardizing adhesion (Carvalho et al, 2004) (Wang and Spencer, 2005).
It is worth mentioning that luting procedures have been previously
performed under a sustained pressure (Goracci et al, 2006). Even if resin
cements benefits from the application of seating pressure during setting, it
is doubtful that this counteracted fluid transudation from the underlying
dentin (Chieffi et al, 2007) (Chieffi et al, 2006). It is more likely that the
thixotropic behaviour of the materials tested, that are maintained in a low
viscosity condition under shear forces, lowered cement thickness allowing
better substrate adaptation (De Munck et al, 2004). It may be speculated
that the percentage of filler and the particle size may have influenced the
results.
93
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Adhes Dent 1999; 1: 299-309.
Sauro S, Pashley DH, Montanari M, Chersoni S, Carvalho RM,
Toledano M, Osorio R, Tay FR, Prati C. Effect of simulated pulpal
96
pressure on dentin permeability and adhesion of self-etch adhesives. Dent
Mater 2007; 23: 705-713.
Tay FR, Pashley DH, Byoung IS, Carvalho RM, Itthagarun A.
Single-step adhesives are permeable membranes. J Dent 2002; 30: 371382.
Tay FR, Pashley DH, Suh BI, Hiraishi N, Yiu CK. Water treeing in
simplified dentin adhesives – déjà vù? Oper Dent 2005; 30: 561-579.
Tay FR, Pashley DH, Yiu C, Cheong C, Hashimoto M, Itou K,
Yoshiyama M, King NM. Nanoleakage types and potential implications:
evidence from unfilled and filled adhesives with the same resin
composition. Am J Dent 2004; 17: 182-190.
Tay FR, Pashley DH, Yiu CH, Sanares AM, Wei SH. Factors
contributing to the incompatibility between simplified-step adhesives and
chemically-cured or dual-cured composites. Part I. Single-step self-etching
adhesive. J Adhes Dent 2003; 5: 27-40.
Tay FR, Pashley DH. Have dentin adhesives become too
hydrophilic? J Can Dent Assoc 2003; 69: 726-731.
Tay FR, Pashley DH. Water treeing – a potential mechanism for
degradation of dentin adhesives. Am J Dent 2003; 16: 6-12.
Van Meerbeek B, Van Landuyt KL, De Munck J, Hashimoto M,
Peumans M, Lambrechts P, Yoshida Y, Inoue S, Suzuki K. Techniquesensitivity of contemporary adhesives. Dent Mater J 2005; 24: 1-13.
Wang Y, Spencer P. Evaluation of the interface between one bottle
adhesive systems and dentin by Goldner’s trichrome. Am J Dent 2005; 18:
66-72.
97
Yip Y, McHugh AJ. Modeling simulation of nonsolvent vapourinduced phase separation. Joutnal of Membrane Science 2005 (on-line
publication).
Yiu CKY, King NM, Carrilho MRO, Sauro S, Rueggeberg FA, Prati
C, Carvalho M, Pashley DH, Tay FR. Effect of resin hydrophilicity and
temperature on water sorption of dental adhesive resin. Biomaterials 2006;
27: 1695-1673.
Yoshida Y, Nagakane K, Fukuda R, Nakayama Y, Okazaki M,
Shintani H, Inoue S, Tagawa Y, Suzuki K, De Munck J, Van Meerbeek B.
Comparative study on adhesive performance of functional monomers. J
Dent Res 2004; 83: 454-458.
Zhou XD, Zhang SC, Huebner W, Ownby PD. Effect of the solvent
on the particle morphology of spray PMMA. Journal of Material Science
2001; 36: 3759-3768.
98
Chapter 4
4.1 The role of smear layer on the bonding quality of self-adhesive
resin cements
Adhesion requires an intimate contact between the luting material
and the dental substrate. During prosthetic restoration, smear layer is
usually formed. The smear layer is composed of a mixture of denatured
collagen and dentinal mineral constituents rearranged after cavity
preparation (Pashley, 1992), This layer is a permeable and disaggregate
substrate
composed
of
penetrable
subunits
that
can
establish
interconnections and permit lateral infiltration (Tay et al, 2001) (Prati et
al, 1995) (Tay et al, 2000). From one side, as dentin is a permeable
substrate, smear layer could limit post-operative sensitivity and excessive
water trasudation (Grégoire et al, 2003). The complete removal of smear
layer would result in an increased water flux through dentinal tubules (Tay
et al, 2005 (Carrilho et al, 2007). The effects of an excessive transdentinal fluid movement were identified in an inhibition of the cement
polymerization and hydrolitic degradation of resins and collagen fibrillar
components, hence hindering optimal seal and bond durability (Sauro et
al, 2007) (Musanje et al, 2003). On the other hand, smear layer may
represent an inadequate area to be bonded (Glasspoole et al, 2002) and
weakened adhesive interfaces are likely to be formed (Tay et al, 2000=
(Oliveira et al, 2003).
According to the adhesive system adopted for the adhesion
mechanism, smear layer can be totally removed (i.e. with phosphoric acid)
or modified and partially dissolved with mild acidic solutions (i.e.
polyacrylic acid or oxalate) or chelating agents (i.e. EDTA). Self-adhesive
99
cements incorporate the smear layer as an intermediate bonding substrate,
reducing the possibility of post-op sensitivity possibly reminding the
adhesion concepts of simplified adhesive systems. Ideally, this bonding
process would result less sensitive to the regional variability of the
substrate (i.e. deep and superficial dentin) compared to that employed by
multi-step cements that utilize a separate acid etching step. Moreover, the
maintance of the dentin mineral component would be beneficial in terms
of bond durability, due to the absence of unprotected collagen fibrils
(Hashimoto et al, 2000) (Kato and Nakabayashi, 1998).
To date, there is no accordance regarding the effective ability of selfadhesive cements to attain a reliable bond strength to dentin. Possibly, the
cements do not possess the capacity necessary to modify the smear layer,
demineralize and simultaneously infiltrate the underneath dentin (Al-Assaf
et al, 2007). Previous studies, demonstrated the negative effects of preconditioning dentin with 35% phosphoric acid (De Munck et al, 2004)
(Hikita et al, 2007). Although the acid completely remove the smear layer
and open up the dentinal tubules, the cements possess an high viscosity
that would impede the diffusion into the conditioned substrate.
In the following investigation, the effect of two mild acidic solutions
(EDTA and/or 10% polyacrylic acid) on the bonding performance of three
self-adhesive cements were tested. The microtensile test was associated
with a scanning electron microscopy evaluation of fractured beams. An
histomorphologic characterization of the adhesive interface with or
without pre-treating dentin was also executed in order to individuate the
efficacy of the cement to penetrate into the partially cleaned dentin.
100
References
Al-Assaf K, Chakmakchi M, Palaghias G, Karanika-Kouma A,
Eliades G. Interfacial characteristics of adhesive luting resins and
composites with dentine. Dent Mater 2997; 23: 829-839.
Carrillho MR, Tay FR, Sworf J, Donnelly AM, Agee KA, Nishitani
NY, Sadek FT, Carvalho RM, Pashley DH. Dentine sealing provided by
smear layer/smear plugs vs adhesive resin/resin tags. Eur J Oral Sci 2007;
115: 321-329.
De Munck J, Vargas M, Van Landuyt K, Hikida K, Lambrechts P,
Van Meerbeeck B. Bonding of an auto-adhesive luting material to enamel
and dentin. Dent Mater 2004; 20: 963-971.
Glasspoole EA, Erickson EL, Davidson CL. Effect of surface
treatments on the bond strength of glass ionomers to enamel. Dent Mater
2002; 18: 454-462.
Grégoire J, Joniot S, Guignes P, Millas A. Dentin permeability: selfetching and one-bottle dentin bonding systems. J Prosthet Dent 2003; 90:
42-49.
Hashimoto M, Ohno H, Kaga M, Endo K, Sano H, Oguchi H. In
vivo degradation of resin-dentin bonds in human over 1 to 3 years. J Dent
Res 2000; 79: 1385-1391.
Hikita K, Van Meerbeek B, De Munck J, Ikeda T, Van Landuyt K,
Maida T, Lambrechts P, Peumans M. Bonding effectiveness of adhesive
luting agents to enamel and dentin. Dent Mater 2007; 23: 71-80.
Kato G, Nakabayashi N. The durability of the adhesion to
phosphoric acid etched, wet dentin substrate. Dent Mater 1998; 14: 347352.
101
Musanje L, Darvell BW. Aspects of water sorption from the air,
water and artificial saliva n resin composite restorative materials. Dent
Mater 2003; 19: 414-422.
Oliveira S, Pugach M, Milton J, Watanabe L, Marshall S, Marshall
G. The influence of the dentin smear layer on adhesion: a self-etching
primer vs. a total-etch system. Dent Mater 2003; 19: 758-67.
Pashley DH. Smear layer overview of structure and function. Proc
Finn Dent Soc 1992; 88: 215-244.
Prati C, Chersoni S, Ferriere P; Mongiorgi R, Davidson CL. Dentine
permeability and bond quality as affected by new bonding systems. J Dent
1995; 23: 217-226.
Sauro S, Pashley DH, Montanari M, Chersoni S, Carvalho RM,
Toledano M, Osorio R, Tay FR, Prati C. Effect of simulated pulpal
pressure on dentin permeability and adhesion of self-etch adhesives. Dent
Mater 2007; 23(6): 705-13.
Tay FR, Carvalho RM, Sano H, Pashley DH. Effect of smear layer
on the bonding of a self-etching primer to dentin. J Adhes Dent 2000; 2:
99-116.
Tay FR, Carvalho RM, Sano H, Pashley DH. Effect of smear layers
on the bonding of a self-etching primer to dentin. J Adhes Dent 2000; 2:
99-116.
Tay FR, Pashley DH, Hiraishi N, Imazato S, Rueggeberg FA, Salz
U, Zimmermann J, King NM. Tubular occlusion prevents water-treeing
and trhough-and-through fluid movement in a single-bottle, one step selfetch adhesive model. J Dent Res 2005; 891-896.
102
Tay FR, Pashley DH. Aggressiveness of contemporary self-etching
systems: I: depth of penetration beyond dentin smear layers. Dent Mater
2001; 17: 296-308.
103
4.2 Dentin treatment effects on the bonding performance of selfadhesive resin cements.
Claudia Mazzitelli, Francesca Monticelli, Manuel Toledano, Marco
Ferrari, Raquel Osorio. European Journal of Oral Sciences, in press.
Introduction
Self-adhesive resin cements were introduced to lute indirect
restorations, such as all-ceramic crowns, composite inlays/onlays or fiber
posts with a simple and standardized approach. The use of self-adhesive
cements is accomplished by a single clinical step, where a simultaneous
demineralization/infiltration of the substrate is expected to occur. Previous
studies revealed dentin bond strength values of some self-adhesive
cements comparable to those of conventional resinous luting agents
(Piwowarczyk et al, 2007) (Bitter et al, 2006). However, the bonding
effectiveness of these simplified cements on smear layer-covered dentin
still remain a concern (Mazzitelli et al, 2008) (De Munck et al, 2004)
(Goracci et al, 2006).
Recent
studies
reported
that
self-adhesive
cements
might
superficially interact with dentin, leading to smear layer partial
demineralization and short resin tags formation (Mazzitelli et al, 2008)
(Monticelli et al, 2008) (Al-Assaf et al, 2007). The presence of partially
demineralized/infiltrated smear layer at the adhesive interface may result
in a relatively poor bonding mechanism (De Munck et al, 2004)
(Glasspoole et al, 2002) and weak adhesive interfaces are likely to be
formed (Tay et al, 2000) (Oliveira et al, 2003). Although self-adhesive
104
cements do not require pre-treatment of the dental substrate, previous
removal of the smear layer with acidic solutions has been proposed in
order to enhance a direct cement/dentin interaction and bond strength
improvement (De Munck et al, 2004) (Hikita et al, 2007) (Behr et al,
2004). It is noteworthy that dentin conditioning with 35% phosphoric acid
before luting with an auto-adhesive luting material was ineffective or
detrimental (De Munck et al, 2004) (Hikita et al, 2007). The use of milder
acidic agents (i.e. EDTA and polyacrilic acid) was suggested (De Munck
et al, 2004) (Monticelli et al, 2008) (Behr et al, 2004). These conditioning
agents could partially remove the smear layer, leaving the dentin mineral
phase, ideally enhancing the chemical reaction between the cement and the
substrate (Monticelli et al, 2008).
Most self-adhesive cements contain functional methacrylated
phosphoric ester monomers and little is known about their chemical
interaction potentials with hydroxiapatite (Mine et al, 2009). Adhesion
may also be dependent on the chemical formulation and physical
properties (i.e. wetting) of the cement (Sarr et al, 2009). Therefore, selfadhesive cements containing hydrophilic compounds (4-META, HEMA)
or solvents (water, HEMA) were included in the study.
The purpose of this study was to compare the dentin/cement bond
strengths and the interfacial characteristics of three commercial adhesive
cements as a function of different pre-treatment regimens. A staining
technique for optical microscopy, that specifically identifies depth of
decalcification/infiltration or exposed collagen at the dentin/cement
interface, was employed. SEM analysis of debonded surfaces was also
performed.
105
The null hypothesis tested was that dentin treatments do not
influence the bond strengths or the morphologic characteristics of the selfadhesive resin cement-dentin interfaces.
Materials and Methods
Samples preparation
Forty-five intact, non-carious human third molars were employed
after the institutional informed consent from all donators. The protocol
was approved by the Research Ethics Commission. Molars were stored in
0.5% Chloramine T solution at 4°C for less than one month. Teeth were
decoronated to expose flat, enamel-free, deep-coronal dentin surfaces. The
pulp chamber of each tooth was exposed after cutting the root below the
CEJ with a slow speed diamond saw (Isomet, Buehler Ltd, Lake Bluff, Il,
USA) under water-cooling. The pulp tissue was carefully removed with a
forceps, being worry to not touch the pulp chamber walls.
Two 2-mm thick increments of a nano-filled hybrid light-cured
composite (Aelite All-Purpose Body, Bisco, Schaumburg, IL, USA, shade
A3, Batch n° 0500002461) were layered in a split aluminium mold (Ø 8
mm x 4 mm height) to prepare composite cylinders. Each increment was
light-cured for 40 s with an halogen-curing light (Astralis 7, Ivoclar
Vivadent, Schaan, Liechtenstein, 600 mW/cm2). Composite cylinders were
removed, additionally light-cured from four aspects for 40 s each and on
the portion previously in contact with the metallic surface of the mold.
Bonding procedure
Each tooth was glued with cyanoacrylate (Super Attak Gel, Henkel
Loctite Adesivi, s.r.l. Milan, Italy) to a Plexiglass slab (1.5 x 1.5 x 0.5 cm).
106
On one side of each Plexiglass plate a fissure was created with a diamond
bur and a short length of 18-gauge stainless steel tube was glued parallel to
the platform extending 2 cm out from it (Ciucchi et al, 1995). A
polyethylene tubing joined each slab-tooth assemblage to a 20 ml syringe.
All syringes were filled with deionised water to produce a simulated
hydrostatic pulpal pressure of 15 cm of H2O at the dentin surface. A thin
smear layer was produced on dentin with #180 SiC-paper.
Three experimental groups (n=15) were prepared according to the
dentin pre-treatment: 1) No dentin pre-treatment; 2) 0.1 M EDTA (pH 7.4)
was scrubbed onto the dentin surfaces with a micro-brush for 60 s and then
rinsed with deionised water for 10 s; 3) 10% polyacrylic acid (Voco,
Cuxhaven, Germany, Lot: 691545) was applied with a micro-brush for 30
s, water rinsed for 30 s.
Resin composite cylinders were luted to the prepared dentin surface
(n=5 each group) with: 1) RelyX Unicem (3M ESPE, Seefeld, Germany) a
hydrophobic and solvent-free self-adhesive cement; 2) Bis-Cem (Bisco,
Schaumburg, IL, USA), an HEMA-based self-adhesive cement; 3) G-Cem
(GC corp., Tokyo, Japan) a 4-META-based and water containing selfadhesive cement. Materials were handled according manufacturers’
recommendations at room temperature (23.0°C ± 1.0°C) and relative
humidity (50% ± 5%). pH of each material was measured. After mixing,
the material was dispensed on pH indicator strips with narrow ranges (0.01.8; 1.8-3.8; 3.8-5.5; Panreac Química, Barcelona, Spain). Application
mode, chemical composition and pH values of the tested materials are
reported in Table 1.
A constant standardized pressure of 40 g/mm2 by means of a metallic
tool was applied (Goracci et al, 2006); the seating force was maintained
107
for the first 5 minutes leaving the material to set in the self-curing
modality. Additional 20 s of light irradiations (Astralis 7, 600 mmW/cm2;
the tip was maintained at a distance of 5mm) from each side of the
specimen and at the top of the restoration previously in contact with the
metal were performed in order to ensure an optimal polymerization
(Vrochari et al, 2009).
Three bonded specimens per group were stored in a laboratory oven
(37°C and 100% relative humidity) maintaining the simulated hydrostatic
pulpal pressure for one month until the microtensile bond strength test.
Microtensile bond strength test
Specimens were detached from the Plexiglass slab with a scaffold,
taking care to not touch and stress the bonded interfaces. Each tooth was
sectioned vertically into 1 mm-thick slabs with a slow-speed cut off
diamond wheel (Isomet) under copious water cooling. Each slab was then
serially sectioned into 0.9 x 0.9 mm sticks, according to the ―nontrimming‖ technique of the microtensile test. Each stick was measured
with a digital caliper (Orteam s.r.l, Milan, Italy), glued with cyanoacrylate
(Super Attack Gel) to the free-sliding doors of a jig and stressed to failure
in tension by means of a universal testing machine (Triax Digital 50,
Controls, Milan, Italy; cross-head speed: 0.5 mm/min).
Prematurely fractured sticks were included in the statistical analysis
and considered as ―zero bond‖ values. The normal and equal distribution
of the bond strength data was first checked by Kolmogorov-Smirnoff and
Levene’s tests, respectively. As bond strength values were not normally
distributed, Kruskall-Wallis Analysis of Variance was used to analyze the
differences in bond strengths among the experimental groups (p<0.05)
108
with the bond strength as the dependent variable, surface conditionings
and luting cements as factors. A series of Mann-Whitney tests (p<0.001)
were used for post-hoc comparisons. Calculations were handled using the
SPSS 14.0 software (SPSS Inc.; Chicago, IL, USA).
Failure modes were examined by a single operator under a
stereomicroscope (Olympus SZ-CTV, Olympus, Tokyo, Japan) at 40x
magnification and classified as cohesive (within the cement, dentin or
composite), adhesive (between the restoration and the cement or at the
luting agent/dentin level) or mixed (adhesive and cohesive fractures
occurred simultaneously).
Scanning electron microscope evaluation (SEM)
Three fractured sticks were selected from each experimental group
and dehydrated with ascending ethanol solutions and air-dried, mounted
on metallic stubs, gold-sputtered (Polaron Range SC 7620, Quorum
Technology, Newhaven, UK) and evaluated under a Scanning Electron
Microscope (SEM, JSM-6060LV, Jeol, Tokyo, Japan) at different
magnifications.
Light microscopy – Masson’s trichrome staining technique
After 24-h, two remaining bonded teeth per group were sectioned
perpendicularly to the bonded interface into 1-mm thick slabs using a lowspeed diamond wheel under water cooling (Isomet 1000). A total of eight
sections were analyzed for each experimental group. The medial aspect of
each resin-dentin bonded slab was glued on methacrylate supports with a
photo-curing adhesive (Technovit 7200 VLC, Kulzer, Norderstedt,
Germany) and grinded with an Exakt polishing machine (EXAKT
109
Technologies Inc., Oklahoma City, OK, USA) using SiC abrasive wet
paper of increasing fine grits (# 800; 1200; 2500; 4000) until getting a
thickness of 5-6 µm. Sections were treated with Masson’s trichrome acid
staining technique (Monticelli et al, 2008) (Erhardt et al, 2008). Each slide
was then cover-slipped and ready to be examined using a light microscope
(BH2, Olympus, Tokyo, Japan).
Table 1. Chemical composition, pH values and application modality of the tested self-adhesive
resin cements.
Material
Composition
Application
RelyX Unicem
(3M ESPE)
Batch n°: 270644
pH: 2.1
Powder: glass fillers, silica,
calcium hydroxide, selfcuring initiators, pigments,
light-curing
initiators,
substituted
pyrimidine,
peroxy compound. Liquid:
methacrylated
phosphoric
esters,
dimethacrylates,
acetate, stabilizers, selfcuring initiators, light-curing
initiators
Mix cement. Apply,
self-cure (5 min) and
light-cure (40s).
Bis Cem
(Bisco)
Batch n°: 0600010898
pH: 2.1
G-Cem
(GC Corp.)
Batch n°: 0611091
pH: 2.7
Bis
(Hydroxyethyl
methacrylate)
phosphate
(Base); Tetraethylene glycol
dimethacrylate; dental glass.
UDMA; phosphoric acid
ester monomer; 4-META;
water; dimethacrylates; silica
powder; initiators/stabilizers;
fluoro-amino-silicate glass.
Auto-Mix
cement.
Apply, self-cure (5
min) and light-cure
(40s).
Mix cement. Dispense,
self-cure (5 min) and
light-cure (40s)
110
Results
Microtensile bond strength test
Mean microtensile bond strengths and standard deviations (SD)
recorded in the experimental groups are displayed in Table 2. Bond
strengths were influenced by dentin pre-treatment and luting cement
(p<0.05).
No differences were evidenced for the hydrophobic and solvent-free
cement (RelyX Unicem) after the different tested conditioning modes. The
HEMA-based self-adhesive cement (Bis-Cem) recorded higher bond
strengths when luted to non treated dentin; bond strength values dropped
after EDTA or after polyacrylic acid treatments, without differences
between these two groups. Bond strengths of the 4-META-based and
water containing cement (G-Cem) significantly increased after 10%
polyacrylic acid etching.
The percentage of pre-testing failures and fracture classification
recorded in the experimental groups are presented in Table 3. The most
frequently observed fracture modes were adhesive between cement and
dentin surface or cohesive within the cement. The number of cohesive
failures increased after treating dentin with EDTA or polyacrilic acid.
Mixed failures were also assessed for all the cements on non treated
dentin.
111
Table 2. Mean microtensile bond strength (SD) values (MPa) and post-hoc comparisons
results obtained for the experimental groups (n=3). Different letters in each column and
asterisks in each row indicate significant differences (p<0.005).
Experimental
Groups
No-Treated
dentin
EDTA
PAA
RelyX
Unicem
16.73(12.5) B
12.4(9.9) B
14.87(15.5) B
Bis-Cem
12.29(11.1) AB*
7.47(8.4) A
6.36(9.4) A
G-Cem
8.03(8.2) A
10.3(8.4) AB
13.47(11.5) B*
Table 3. Percentage of failures recorded in each experimental group. PF: premature
failures; A: adhesive (at the cement/composite or cement/dentin interfaces); C: cohesive
(within the cement); M: mixed (a combination of A and C).
Exp.
Groups
Failure
mode
RelyX
Unicem
No-Treated dentin
EDTA
PAA
PF
A
C
M
PF
A
C
M
PF
A
C
M
23%
36%
37%
27%
33%
47
%
53%
0
%
38%
28%
72%
0%
Bis-Cem
34%
50%
33%
17%
63%
39
%
61%
0
%
61%
0%
100
%
0%
G-Cem
48%
40%
43%
17%
24%
32
%
57%
11
%
30%
21%
79%
0%
112
Scanning electron microscopy (SEM) analysis
Debonded dentin surfaces are shown in Fig. 1.
When the hydrophobic cement (RelyX Unicem) was used on non
treated dentin, voids and bubbles within the cement were observed.
Structural defects consisting on compartimentized honeycombs and resin
globules were detectable (Fig. 1A). When EDTA-treated surfaces were
observed, an alternation of filamentous debris and voids within the cement
layer were found (Fig. 1B). At the polyacrylic acid etched group an area of
cohesive dentin fracture was detected, smear layer removal and opened
dentinal tubules were noticed and some protruding resin tags were
evidenced (Fig. 1C). When using the HEMA-based luting agent (BisCem), partial removal of smear layer and presence of a compact cement
layer still adhered to the dental substrate were seen (Fig. 1D). In the
EDTA-treated group, a more porous cement layer was evident (Fig. 1E).
When the cement was bonded to polyacrilic acid etched dentin, dentinal
tubules were visibly opened with limited resin tag formation (Fig. 1F). The
4-META-based self-adhesive cement (G-Cem) completely covered the
underneath non-treated dentin (Fig. 1G). Tubules partially opened, with
some resin tags and cement remnants adhered to the underlying substrate
were assessed when the material was luted on EDTA treated dentin (Fig.
1H). After polyacrylic acid etching, dentinal tubules were opened and
cement infiltrations encountered at the intertubular dentin (Fig. 1I).
113
Fig. 1: SEM images of debonded sticks (dentin side) after microtensile bond strength test.
Each debonded stick (dentin side) is shown at 85x, while zones shown at higher magnifications are
marked with white asterisks. A) RelyX Unicem on non treated dentin; B) RelyX Unicem and
EDTA treated dentin; C) RelyX Unicem and polyacrylic acid etched dentin; D) Bis-Cem luted on
non treated dentin; E) Bis-Cem and EDTA demineralized dentin; F) Bis-Cem on polyacrylic acid
dentin; G) G-Cem on non treated dentin; H-I) G-Cem on EDTA and polyacrylic acid treated
dentin, respectively.
114
Light microscopy – Masson’s trichrome staining technique
Light microscopy images of cement/dentin interfaces after the
Masson’s trichrome staining are presented in Fig. 2, where the dentin
minerals stain green, the unprotected proteins stain red and the cement
appears beige.
No demineralization was seen for the HEMA-based and 4-METAbased self-adhesive cements when luted to non-treated dentin (Figs. 2D
and G). Slight purple spots and a narrow light red layer, representing mild
collagen demineralization, were observed at the bottom of the adhesive
interface when the hydrophobic and solvent-free cement was used on non
treated or polyacrylic acid etched dentin respectively, but no clear dentin
infiltration could be assessed (Figs. 2A and C). When the same selfadhesive cement was luted on EDTA decalcified dentin, no signs of
demineralization/infiltration were observed (Fig. 2B). Dentin was
infiltrated when the HEMA-based cement (Bis-Cem) was applied onto
EDTA or polyacrylic acid treated dentin (Figs. 2E and F). The cement
containing 4-META and water (G-Cem) seemed to infiltrate the EDTA
and/or polyacrylic acid treated dentin (Figs. 2H and I). Short and sparsely
distributed resin tags formations were noticed at the cement/dentin
interfacial levels, although areas of partially exposed collagen fibrils
(purple spots) not enveloped by resin were present beneath the cement
(Fig. 2I).
115
Fig. 2: Light microscopy images of cement/dentin interfaces stained with Masson’s
trichrome on non treated, EDTA and polyacrylic acid etched dentin: mineralized dentin (green),
resin cement (beige), exposed collagen (red). A) RelyX Unicem on non treated dentin: slight purple
intermittent spots immediately beyond the cement were evidenced, but no resin penetration could
be assessed; B) RelyX Unicem/EDTA; C) RelyX Unicem/polyacrylic acid; D-E-F) Bis-Cem
bonded non non treated, EDTA and polyacrylic acid treated dentin, respectively; G) G-Cem and
non treated dentin; H-I) G-Cem on EDTA and polyacrylic acid treated dentin, respectively.
116
Discussion
The null hypothesis must be rejected since both dentin pre-treatment
and cement type influenced the microtensile bond strengths of selfadhesive cements to dentin. The interfacial characteristics of the selfadhesive cements-dentin interfaces varied according to the performed
surface treatment. Reproducing a positive intra-pulpal pressure during
luting procedures, resulted in different bonding performances when selfadhesive cements where used for the cementation of composite overlays
(Mazzitelli et al, 2008). The maintenance of the hydration state of dentin
was suppose to optimize the chemical reaction of selected self-adhesive
cements. For this reason, a simulated pulpal pressure was applied during
cementation and preserved until testing in the present study.
No differences in bond strengths were observed when the
hydrophobic and solvent-free self-adhesive cement (RelyX Unicem) was
tested in the three experimental conditions (Table 2). The calcium
chelating ability of EDTA produced slight smear layer and smear plug
removal and, although no increase in surface roughness is expected
(Osorio et al, 2007), the cement appeared partially adherent to the bonded
substrate (Fig. 1B). After polyacrylic acid etching dentinal tubules were
visibly opened, inter-tubular dentin was exposed and limited resin
infiltration could be observed (Fig. 1C). Exposed and un-enveloped
collagen network at the bottom of the adhesive interface were also noticed
by light microscopy (purple spots) (Fig.2C). The maintenance of dentinal
inter-fibrillar mineral components (after tested dentin treatments) has been
suggested to facilitate the chemical bonds with the cements and ideally
117
promote resin infiltration (De Munck et al, 2004) (Monticelli et al, 2008)
(Hikita et al, 2007). However, no increase in bond strength was assessed
for this solvent-free cement after EDTA or polyacrilic acid dentin
treatments (Table 2). The viscosity of the material will hamper cement
penetration into dentin (De Munck et al, 2004) (Behr et al, 2004) (Cantoro
et al, 2008) (Lührs et al, 2009): although dentin pre-treatment produces
opened and plug-free dentinal tubules (Osorio et al, 2005) (Habelitz et al,
2002) (Erhardt et al, 2008), no further resin infiltration would be promoted
(Gerth et al, 2006). Collagen mesh activation by tested mild acids agents
neither improves bonding values of the hydrophobic auto-adhesive cement
(Gerth et al, 2006).
Pre-treatment of dentin caused a significant drop of the HEMAbased cement (Bis-Cem) bond strengths (Table 2). Demineralised and non
infiltrated dentin was not found at the light microscopy images of these
bonded interfaces, when dentin was pre-treated with EDTA or polyacrylic
acid (Figs. 2E and F). The cement is composed by a mixture of BisHEMA and, in a lower percentage, of TEGDMA as a diluent agent (Table
1). HEMA is a water-soluble molecule that promote resin infiltration into
demineralised dentin (Nakabayashi and Takarada, 1992), but it can also
attracts water from the underneath perfused dental substrate, leading to
poor polymerization (Nunes et al, 2005), and mechanical properties
decrease, jeopardizing bonding performances (Carvalho et al, 2004) (Van
Landuyt et al, 2008). Water exposure would also exert a detrimental
plasticization effect (Nunes et al, 2005) (Carvalho et al, 2004). The water
content of the dentin has differential effects on the bond strengths of selfadhesive cements (Mazzitelli et al, 2008). After dentin conditionings (in
the presence of pulpal pressure) the gradient of water fluid flow will
118
increase at the bonded interfaces causing water entrapment within this
HEMA-rich material (Carvalho et al, 2004) (Van Landuyt et al, 2007).
The accumulation of water within the cement will give the material a
porous appearance when bonded on perfused, treated dentin (Fig. 1E).
Filamentous formations onto the treated dentin surfaces and non-resin
filled opened dentinal tubules were assessed after treating dentin with
polyacrylic acid (Fig. 1F). The high number of cohesive failures registered
for the Bis-HEMA-based cement after pre-treating dentin with EDTA
and/or polyacrylic acid (Table 3) suggests that the bond strength decrease
will be related to the inherent weakness of the material in presence of
abundant water.
Polyacrylic acid etching of dentin caused a significant increase in
bond strength for the 4-META-based cement (G-Cem) (Table 2).
According to the manufacturer, this cement exhibits a glass-ionomer like
technology. It contains water, fluoro-alumino-silicate glass and phosphoric
acid esters (Table 1), and therefore a setting reaction similar to that of
silicate cements may occur (Anusavice, 2003). A chemical interaction
between the cement and the dentinal mineral content may also be expected
after polyacrylic acid application (Wilson et al, 1983). Treating dentin
with this acidic solution may result beneficial in activating ions (i.e. P and
Ca+) from the dental substrate that can be incorporated into the cement
mass and enhance a chemical reaction between the cement and the dentin
(Tay et al, 2007) (Yoshida et al, 2001). Polyacrylic acid application will
also increase dentin surface roughness facilitating micromechanical
retentions being a clear benefit for the bonding process. The interfacial
evaluation revealed a slight discrepancy between etching depth and
cement penetration (a slight narrow purple line at the bottom of the resin
119
layer) (Fig. 2I). The limited diffusion of this viscous filled cement may
produce an area of exposed and non-resin impregnated collagen layer at
the adhesive joint, that is prone to premature degradation (Wang and
Spencer, 2005) (Spencer et al, 2004) (Hashimoto et al, 2003). EDTA
treatment of dentin did not improve the bond strengths of this cement
based upon a glass-ionomer technology. EDTA exerts just a slight smear
layer removal and does not increase surface roughness (Osorio et al, 2007)
(Osorio et al, 2005), hence mechanical interlocking within the intertubular
dentin will not be facilitated (Coli et al, 2003). However, EDTA treatment
caused opening of dentinal tubules that resulted in some resin tags
formations (Fig. 2H). It remains to be proved if a previous application of
adhesives as intermediate layers would be beneficial in promoting cement
penetration (Hikita et al, 2007) (Behr et al, 2004) (Lürhs et al, 2009). Selfadhesive cements are a heterogeneous subgroup of resin cements and there
are substantial differences between them in terms of setting reaction,
chemical composition and pH. It is clear that a more specific classification
of these new-marketed materials is needed. More information from
manufacturers regarding their exact chemical compositions and further
research will be highly desirable.
Within the limits of this study, it may be concluded that selfadhesive cements were not able to completely demineralise/dissolve the
smear layer and no decalcification/infiltration of dentin was observed.
Dentin conditioning facilitates smear layer removal, but the viscosity of
the materials hampers their penetration into dentin. Opening of dentinal
tubules permits resin tags formations, but also produces a water flow that
may affect bond strengths. The exact bonding mechanism of these
simplified materials remains to be ascertained.
120
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Behr M, Rosentritt M, Regnet T, Lang R, Handel G. Marginal
adaptation in dentin of a self-adhesive universal resin cement compared
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Bitter K, Meyer-Lueckel H, Priehn K, Kanjuparambil JP, Neumann
K, Kielbassa AM. Effect of luting agent and thermocycling on bond
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Cantoro A, Goracci C, Papacchini F, Mazzitelli C, Fadda GM,
Ferrari M. Effect of pre-cure temperatures on the bonding potential of selfetch and self-adhesive resin cements. Dent Mater 2008; 24: 577-83.
Carvalho RM, Pegoraro TA, Tay FR, Pegoraro LF, Silva NRFA,
Pashley DH. Adhesive permeability affects coupling of resin cements that
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Ciucchi B, Bouillaguet S, Holz J, Pashley DH. Dentinal fluid
dynamics in human teeth, in vivo. J Endod 1995; 21: 191-94.
Coli P, Alaeddin S, Nennrberg A, Karlsson S. In vitro dentin pretreatment: surface roughness and adhesive shear bond strength. Eur J Oral
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De Munck J, Vargas M, Van Landuyt K, Hikita K, Lambrechts P,
Van Meerbeek B. Bonding of an auto-adhesive luting material to enamel
and dentin. Dent Mater 2004; 20: 963-71.
Erhardt MC, Osorio R, Toledano M. Dentin treatment with MMPs
inhibitors does not alter bond strengths to caries-affected dentin. J Dent
2008; 36: 1068-73.
Erhardt MC, Toledano M, Osorio R, Pimenta LA. Histomorphologic
characterization
and
bond
strength
evaluation
of
caries-affected
dentin/resin interfaces: Effects of long-term water exposure. Dent Mater
2008; 24: 786-98.
Gerth HU, Dammaschke T, Zuchner H, Schafer E. Chemical
analysis and bonding reaction of RelyX Unicem and Bifix composites—a
comparative study. Dent Mater 2006; 22: 934-41.
Glasspoole EA, Erickson EL, Davidson CL. Effect of surface
treatments on the bond strength of glass-ionomer to esame. Dent Mater
2002; 18: 454-52.
Goracci C, Cury AH, Cantoro A, Papacchini F, Tay FR, Ferrari M.
Microtensile bond strength and interfacial properties of self-etching and
self-adhesive resin cements used to lute composite onlays under different
seating forces. J Adhes Dent 2006; 8: 327-35.
Habelitz S, Balooch M, Marshall SJ, Balooch G, Marshall GW. In
situ atomic force microscopy of partially demineralized human dentine
collagen fibrils. J Struct Biol 2002; 138: 227-36.
Hashimoto M, Ohno H, Yoshida E, Hori M, Sano H, Kaga M,
Oguchi H. Resin-enamel bonds made with self-etching primers on ground
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Hikita K, Van Meerbeeck B, De Munck J, Ikeda T, Van Landuyt K,
Maida T, Lambrechts P, Peumans M. Bonding effectiveness of adhesive
luting agents to enamel and dentin. Dent Mater 2007; 23: 71-80.
Lührs AK, Guhr S, Günay S, Geurtsen W. Shear bond strength of
self-adhesive resins compared to resin cements with etch and rinse
adhesive to enamel and dentin in vitro. Clin Oral Invest doi:
10.1007/s00784-009-0279-z.
Mazzitelli C, Monticelli F, Osorio R, Casucci A, Toledano M,
Ferrari M. Effect of simulated pulpal pressure on self-adhesive cements
bonding to dentin. Dent Mater 2008; 24: 1156-63.
Mine A, De Munck J, Cardoso MV, Van Landuyt KL, Poitevin A,
Kuboki T, Yoshida Y, Suzuki K, Lambrechts P, Van Meerbeek B.
Bonding effectiveness of two contemporary self-etch adhesives to enamel
and dentin. J Dent 2009; 37: 872-883.
Monticelli F, Osorio R, Mazzitelli C, Ferrari M, Toledano M.
Limited decalcification/diffusion of self-adhesive cements into dentin. J
Dent Res 2008; 87: 974-9.
Nakabayashi N, Takarada F. Effect of HEMA on bonding to dentin.
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Nunes TG, Ceballos L, Osorio R, Toledano M. Spatially resolved
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influence of the dentin smear layer on adhesion: a self-etching primer vs. a
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Osorio R, Aguilera FS, Osorio E, Cabrerizo-Vilchez MA, Toledano
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conditioning treatment. Ab. #1515; IADR, 21-24 March 2007; New
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Res 2005; 84: 736-40.
Piwowarczyk A, Bender R, Ottl P, Lauer HC. Long-term bond
between dual-polymerizing cementing agents and human bond dental
tissue. Dent Mater 2007; 23: 211-217.
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Van Meerbeek B, Van Landuyt KL. Immediate bonding effectiveness of
contemporary composite cements to dentin. Clin Oral Investig 2009; Doi:
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Spencer P, Wang Y, Katz JL. Identification of collagen
encapsulation at the dentin/adhesive interface. J Adhes Dent 2004; 6: 9195.
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bonding of a self-etching primer to dentin. J Adhes Dent 2000; 2: 99-116.
Tay FR, Pashley DH, Kapur RR, Carrilho MRO, Hur HB, Garrett
LV, Tay KCY. Bonding Bis-GMA to dentin—A proof of concept for
hydrophobic dentin bonding. J Dent Res 2007; 86: 1034-39.
Van Landuyt KL, Snauwaert J, De Munck J, Coutinho E, Poitevin A,
Yoshida Y, Suzuki K, Lambrechts P, Van Meerbeek B. Origin of
interfacial droplets with one-step adhesives. J Dent Res 2007; 86: 739-44.
Van Landuyt KL, Snauwaert J, Peuman S, De Munck J, Lambrechts
P, Van Meerbeek B. The role of HEMA in one-step self-etch adhesives.
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Vrochari AD, Eliades G, Hellwig E, Wrbas KT. Curing efficiency of
four self-etching, self-adhesive resin cements. Dent Mater 2009; doi:
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Wilson AD, Prosser HJ, Powis DM. Mechanism of adhesion of
polyelectrolyte cements to hydroxyapatite. J Dent Res 1983; 62: 590-592.
Yoshida Y, Van Meerbeek B, Nakayama J, Yoshioka M, Snauwaert
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125
Chapter 5
5.1 Self-adhesive cements and fiber posts
Fiber post are clinically used to restore endodontically treated teeth
with massive coronal distruction and they are necessary to increase the
retention of the coronal restoration. Their clinical behaviour and
mechanical properties have been widely investigated (Ferrari et al, 2003)
(Grandini et al, 2005) (Malferrari et al, 2003) (Cagidiaco et al, 2007)
(Ferrari et al, 2007). Factors that may affect the bonding of fiber posts to
root canal dentin are considered the lack of direct vision due to the
restricted access (D’Arcangelo et al, 2008a), the difficult control of
moisture when using multi step systems (Toba et al, 2003), the type of
luting agents (Akgunkor et al, 2006) (Bitter et al, 2006) and the cementing
techniques (D’Arcangelo et al, 2008b). Although a vertical root fracture
represents the most severe cause of irreparable failure, all these factors
may contribute to a premature loss of retention at both dentin/cement or
cement/post interfaces.
In a context in which the concept of a post/cement/root dentin
monoblock unit results quite unpredictable, the type of luting agent,
intended as the physical join between post and dentin, become the
instrument for obtaining a reliable restoration. Several luting material have
been proposed over the year for the cementation of fiber posts, although
resin cements showed good mechanical properties and were related to
higher dilocant resistance when compared to conventional cements.
Information regarding the ability of self-adhesive cements to lute fiber
posts is relatively present in literature and contrasting results in the
immediate and long-term data could be noticed. To date, different selfadhesive cements are available in the market. Differences in their chemical
126
composition would influence their bonding mechanism, that is each
material should be considered indenpdent of the class it belong to.
In this chapter, the bonding potential of different cements was
evaluated with the push-out test. Thermal ageing was performed in the
second study in order to forese whether simplified composite cements
would resist to the physiologic changes that occur in the oral cavity.
127
References
Akgungor G, Akkayan B. Influence of dentin bonding agents and
polymerization modes on the bond strengths between translucent fiber
posts and three dentin regions within a post space. J Prosthet Dent 2006;
95: 368-378.
Bitter K, Priehn K, Martus P, Kielbassa AM. In vitro evaluation of
push-out bond strengths of various luting agents to tooth-colored posts. J
Prosthet Dent 2006; 95: 302-310.
Cagidiaco MC, Radovic I, Simonetti M, Tay FR, Ferrari M. Clinical
performance of fiber post restorations in endodontically treated teeth: 2year resultas. Int J Prosthodont 2007; 20(3): 293-298.
D’Arcangelo C, D’Amario M, Vadini M, Zazzeroni S, De Angelis F,
Caputi S. An evaluation of luting agent application technique effect on
fibre post retention. J Dent 2008b; 36: 235-240.
D’Arcangelo C, Zazzeroni S, D’Amario M, Vadini M, De Angelis F,
Trubiani O, Caputi S. Bond strength of three types of fibre-reinforced post
systems in various regions of root canals. Int Endod J, 2008a; 42: 322-328.
Ferrari M, Cagidiaco CM, Goracci C, Vichi A, Mason PN, Radovic
I, Tay FR. Long-term retrospective study of the clinical performance of
fiber posts. Am J Dent 2007; 20(5): 287-291.
Ferrari M, Vichi A, Mannocci F, Mason PN. Retrospective study of
clinical behaviour of several types of fiber posts. Am J Dent 2003; 13:
14B-19B.
Grandini S, Goracci C, Monticelli F, Tay FR, Ferrari M. Fatigue
resistance and structural integrity of fiber posts: three-bending test and
SEM evaluation: Dent Mater 2005; 21: 75-82.
128
Malferrari S, Monaco C, Scotti R. Clinical evaluation of teeth
restored with quartz fiber-reinforced epoxy resin posts. Int J Prosthodont
2003; 16(1): 39-44.
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129
5.2 Evaluation of the push-out bond strength of self-adhesive resin
cements to fiber posts
Claudia Mazzitelli, Francesca Monticelli. International Dentistry of South
Africa, in press.
Introduction
Fiber
posts
are
increasingly
used
for
the
restoration
of
endodontically treated teeth with massive coronal distructions. Their
mechanical properties and clinical behaviour have widely been
investigated (Ferrari et al, 2003) (Grandini et al, 2005) (Cagidiaco et al,
2007) (Ferrari et al, 2007) The dislocation resistance of fiber posts into
root canal is significantly influenced by the luting agent and the
cementation procedures (D’Arcangelo et al, 2008a). Resin cements allow
superior post retention and increase the fracture resistance of the postrestored tooth when compared to conventional cements (Bitter et al, 2006)
(D’Arcangelo et al, 2008b) (Qualthrough and Mannocci, 2003)
Several factors contribute to render post luting procedures difficult:
the lack of direct vision and the limited access to the bonding substrate
make cementation procedures very technically-related (D’Arcangelo et al,
2008a). Moisture control within root canals represents an additional
limitation during the management of multi-step resin cements (Chersoni et
al, 2005).
Self-adhesive resin cements simplified luting procedures of indirect
restorations and have been designed to be less technique-sensitive than
their multi-step counterparts. Laboratory investigations found comparable
bond strength values between RelyX Unicem and resin cements that
130
utilized two or three-steps adhesives (Radovic et al, 2008) (Bitter et al,
2006) RelyX Unicem is undoubtedly the most investigated self-adhesive
material, notwithstanding the variety of products that have been launched
by different manufacturers. Self-adhesive cements possess different
chemical compositions and dispensing modalities that could influence
their mechanical properties and bonding performances.
Push-out test is an appropriate method to measure the bond strength
inside the root canals. The shear stresses are created parallel to the
cement/dentin and cement/post interfaces, resulting in a better simulation
of the stress occurring in clinical conditions (Goracci et al, 2007) (Goracci
et al, 2004).
The purpose of the present study was to assess the push-out bond
strength of three self-adhesive resin cements used for the cementation of
epoxy resin-based fiber posts. The null hypothesis tested was that no
differences in bond strength are present among different self-adhesive
resin cements independently from their chemical compositions and
application mode.
Materials and Methods
Specimen preparation
Thirty extracted, single-rooted, carie-free human premolars stored in
0.5% Chloramine T solution at 4° C for preventing bacterial growth were
selected for the study after informed consent of the donors was obtained.
The crown of each tooth was removed 1 mm above the CEJ by means of a
slow speed diamond saw (Isomet, Buehler, Lake Bluff, IL, USA) under
copious water cooling. Working length was established at 1 mm from the
root apex. Cleaning and shaping of the root canal were performed with
131
Protaper Ni-Ti rotatory instruments (size S1, S2, S3; Dentsply Maillefer,
Ballagues, Switzerland) following the crown-down technique. Irrigations
with
5%
sodium
hypochlorite
were
performed
between
the
instrumentations. Gutta-percha cones (Coltène/Whaledent, Langenau,
Germany) were used for filling the root canal and cemented with a resin
sealer (AH Plus Jet, Dentsply DeTrey, Konstanz, Germany) following the
lateral condensation technique. Roots were then coronally sealed with a
temporary restorative material (Fuji VII, GC Corporation, Tokyo, Japan;
batch n° 0410221) and stored in a laboratory oven at 37° C and 100%
relative humidity. After 24 hours, the temporary seal was abraded by
means of #240 SiC paper under water cooling, and the coronal guttapercha was removed with a pre-shaping drill (Dentsply DeTrey, Konstanz,
Germany), leaving a 5 mm-long apical seal. A 7 mm-deep post space was
prepared with a universal drill (3M ESPE, Seefeld, Germany) to match the
size of the co-respective RelyX Fiber Post (#1; 3M ESPE, Seefeld,
Germany; LOT: 02363200603). The drilled canal was gently air-blowed in
order to eliminate any residual gutta-percha. Three self-adhesive
composite cements were used for fiber post cementation (n=10): 1. Rely X
Unicem (3M ESPE, Seefeld, Germany); 2. Multilink Sprint (IvoclarVivadent, Schaan, Liechtenstein); 3. Max-Cem (Kerr Corp, Orange, CA,
USA).
Materials were handled according to manufacturer’s instructions.
Application modes, chemical compositions and batch numbers of the
investigated materials are listed in Table 1.
The cements were used in the dual-cured modality. After the first 5
min of auto-cure in which the post was loaded under finger pressure,
additional 40 s of light polymerization through the translucent fiber post
132
were performed (Astralis 7, Ivoclar-Vivadent, Schaan, Liechtenstein;
output: 500 mW/cm2). The cement in excess was carefully removed with a
spatula. A core build-up was performed with Fuji VII (GC corp; LOT:
0703071). Specimens were maintained for 1 month in a flower sponge
slightly wetted with demonized water and stored in a laboratory incubator
(37±1 °C).
Push-out bond strength test
The portion of the root containing the fiber post was subsequently
sectioned into four to six 1 mm-thick slices with a diamond saw (Isomet)
under water cooling. The cylindrical plunger of the testing machine (Triax
50, Controls S.P.A, Milan, Italy) was forced to dislodge, via an apicalcoronal direction, each inverted, truncated fiber post from the root dentin.
A load (0.5 mm/min until failure) was then applied to the post surface that
resulted in shear stresses along the cement/dentin – cement/post interfaces.
The retentive strength of the post fragment (MPa) was calculated by
dividing the load at failure (Newton) by the interfacial area of the post
segment (SL). The formula used for measuring the tronco-conical area was
so expressed:
SL = π (R+r) [(h2+ (R-r)2]0.5
In which π was equal to 3.14, R and r were the coronal and the apical
post radius respectively, and h the root slice thickness. The diameters of
the post and the thickness of the slice were individually measured using a
digital caliper with 0.01 mm accuracy.
Failure modes were evaluated by a single operator under a
stereomicroscope (Olympus SZ-CTV, Olympus, Tokyo, Japan) at 40x
magnification and classified as cohesive (within the post), adhesive
133
(between the post and the cement or at the cement/intra-radicular dentin
level) or mixed (adhesive and cohesive fractures occurred simultaneously).
One stressed-to-failure slice per group was used for scanning
electron microscopy (SEM) evaluation. Specimens were rinsed with
ascending ethanol solutions, mounted on metallic stubs, gold-sputtered
(Polaron Range SC 7620, Quorum Technology, Newhaven, UK) and
observed under a scanning electron microscope (JSM-6060LV, Jeol,
Tokyo, Japan).
Statistical analysis
The normal and equal distributions of the push-out bond strength
data were first checked and verified by the Kolmogorov-Smirnov and
Levene’s test respectively. A one-way ANOVA was performed to verify
the differences in push-out bond strengths between the tested luting
cements (p<0.05). A Tukey test was then executed for post-hoc
comparisons (p<0.001). Calculations were handled by the SPSS 15.0
software (SPSS Inc.; Chicago, IL, USA).
134
Table 1. Manufacturers, chemical compositions and application modes of the materials tested in the
study.
Material
Composition
Delivery system
Instructions for use
Rely X Unicem
(3M ESPE,)
Batch n°:270644
pH= 2.1
Powder: glass fillers, silica,
calcium hydroxide, self-curing
initiators, pigments, light-curing
initiators, substituted pyrimidine,
peroxy
compound.
Liquid:
methacrylated phosphoric esters,
dimethacrylates,
acetate,
stabilizers, self-curing initiators,
light-curing initiators
Dymethacrylates,
adhesive
monomers,
fillers,
initiators/stabilizers
Capsule
and
Aplicap
Elongation Tip
Mix cement. Apply,
self-cure (5 min) and
light-cure (40s)
Paste/paste dual
syringe with a
mixing tip
Automix
cement.
Apply, self-cure (5 min)
and light-cure (40s)
Base:
Uretanedymethacrylate,
Camphoroquinone,
Fluoroaluminosilicate,
others.
Catalyst:
Bis-GMA,
Triethyleneglycoldimethacrylates,
Glycerophosphatedimethacrylates,
Bariumaluminopolosilicate glass,
Others
Paste/paste dual
syringe with a
mixing tip
Automix
cement.
Apply, self-cure (5 min)
and light-cure (40s)
Multilink
Sprint
(IvoclarVivadent)
Batch n°:j22739
pH: 4.2
Max-Cem
(Kerr Dental)
Batch n°:
pH: 2.2
135
Results
Mean push-out bond strengths (SD) and failure modes of the tested
cements are displayed in Table 2. Differences in bond strengths exist
among the self-adhesive cements used for luting fiber posts (p<0.05).
RelyX Unicem exhibited significantly higher bond strengths than the
other tested cements. Push-out values of Multilink Sprint were lower than
those of RelyX Unicem but higher than Max-Cem that recorded the worst
push-out bond strength values.
The failure modes recorded were mostly adhesives in nature both
between dentin and cement and at the post/cement interface. Cohesive
failures were only observed for RelyX Unicem. Mixed failures also
occurred in the three self-adhesive cements investigated. No cohesive
failure within the fiber post were observed in the present study.
Table 2. Push-out strengths and the percentage of slices with their respective failure modes.
Numbers are means (MPa), values in brackets are standard deviations. Different letters show
statistically significant differences (p<0.05). AD: adhesive failures between dentin and luting agent;
AP: adhesive failures between post and cement; C: cohesive failures within the post; M: mixed
failures.
Experimental groups
Sample
size
Failure mode
Mean (SD)
AD
AP
C
M
Rely X Unicem
32
69%
19%
6%
6%
10.27(2.18) A*
Multilink Sprint
31
42%
29%
0%
29%
7.55(3.78) B
Max-Cem
30
33%
57%
0%
10%
3.86(2.94) C
136
Discussion
The results of this study require the rejection of the null hypothesis
since differences in push-out bond strength exist between the tested selfadhesive cements.
The bonding mechanism of self-adhesive cements rely on chemical
interactions and micromechanical retentions with the bonding substrate,
but concerns still exist on the effective adhesive potential of these
simplified cement.
In the present study, RelyX Unicem attained the higher bond
strength values when compared to the other materials. In line with
previous studies, these values may be comparable to those of multi-step
luting agents (Radovic et al, 2008) (Bitter et al, 2006). When compared to
another self-adhesive materials, RelyX Unicem registered the higher bond
strength (Zicari et al, 2008). The use of the cement/post combination as
recommended by the manufacturers, may have counted for the results
obtained (Radovic et al, 2008) (Kececi et al, 2008). In the present study,
only one type of fiber post was used (RelyX Fiber Post, 3M ESPE) as the
main purpose was to estimate the bond strengths of self-adhesive cements.
Differences in the application mode may have similarly influenced the
results. RelyX Unicem utilized an elongation tip during its insertion into
root canal resulting in inferior chance of bubbles formation and airentrapment that would lead to an improvement in the marginal adaptation
of the material both to the dental substrate and to the fiber post (Watzke et
al, 2008). Simonetti and colleagues, addressed the higher sealing ability of
RelyX Unicem dispensed with the elongation tip in comparisons with
137
Max-Cem and others multi-step cements that were inserted into root canal
with a lentulo spiral or directly applied on the post surface (Simonetti et
al, 2008). The two self-adhesive cements employed in the present study
have a paste-to-paste composition. Base and catalyst are mixed together
through an auto-mixing tip on a glass pad and the material was then
inserted into the root canals with lentulo spirals. This method appeared
less feasible as could increase the risk of air entrapment causing the
formation of voids and interfacial defects that expedite premature failure
in presence of cyclic stresses.
Max-Cem attained the worse push-out values (Table 2). The cement
layer appeared inhomogeneous with frank voids and bubbles incorporated
into the bulk (Fig. 1). Max-Cem is considered extremely technicalsensitive and any errors occurring during the mixing process can be
determinant for its physical and mechanical properties (Behr et al, 2008).
A prevalence of adhesive decementation at the cement/post side were
recorded. Max-Cem possess an acidic pH that is maintained high even
after 48 hours from its application. This may exert a detrimental effect on
its physical properties, diminishing the possibility to establish effective
micro-mechanical retentions. Moreover, the presence of an acidic layer on
the post surface may jeopardize the formation of hydrogen bonds between
the cement and fiber post, and the bonding potential of the cement itself
result limited (Wrbas et al, 2007).
Multilink Sprint bond strengths were inferior than those of RelyX
Unicem, but higher than those of Max-Cem. The material was able to
partially demineralise the dental substrate, although discrepancies between
the degree of demineralization and depth of resin penetration was assessed
by light microscopy (Monticelli et al, 2008). At the dentin site bond, the
138
material appeared porous, probably due to an incomplete polymerization
reaction (Fig. 2). The presence of residual acidic monomers at the bottom
of the adhesive interface may represent weak areas as they can retain their
etching potential jeopardizing adhesion (Mazzitelli et al, 2008) (Spencer
and Swafford, 1999). These areas and the presence of collagen fibrils at
the adhesive joint would undergo to premature degradation hence limiting
the bonding potential of the material and reducing the service life of the
restoration (Spencer and Swafford, 1999) (Wang and Spencer, 2005).
Further studies should be performed to assess the longevity of these selfadhesive cements.
Nowadays, many studies are performed using ageing tests to assess
the longevity of bonded interfaces. Several authors found that
thermocycling may increase the retentive strength especially for RelyX
Unicem. The thermal changes were supposed to promote a complete
chemical polymerization enhancing its bonding potential (Bitter et al,
2006) (Reich et al, 2005). Self-adhesive cements work as dual-cure
materials, where the chemical polymerization can be completed by light
irradiation (Radovic et al, 2008b). Anyway, doubts exist on the degree of
monomer conversion of the simplified cements. Some authors attained
inferior bond strengths and decreased mechanical properties when RelyX
Unicem was only auto-cured (Vrochari et al, 2009) (Piwowarczyk et al,
2003) (Kumbuloglu et al, 2004). No differences in the degree of monomer
conversion were found between RelyX Unicem and Multilink Sprint,
whereas Max-Cem attained the lower values (Vrochari et al, 2009).
Several factors may count for the differences recorded, first of all the
diverse chemical formulations. However, few information are furnished by
139
manufacturers and more specific details are highly desirable in order to
define their characteristics and bonding behaviour.
Fig. 1. Representative SEM image of Max-Cem after the push-out test (45x). Voids are
detected within the cement bulk, possibly due to air-entrapment during the mixing and insertion
procedures.
Fig. 2. SEM microphotographs of Multilink Sprint (20 bar, original magnification: 350X).
A detachment of the fillers from the resinous matrix showing a porous appearance was assessed
when the material was submitted to shear forces.
140
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Kececi AD, Kaya U, Adanir N. Micro push-out bond strengths of
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144
5.3 Effect of thermocycling on the bond strength of self-adhesive
cements to fiber posts
Claudia Mazzitelli, Francesca Monticelli, Manuel Toledano, Marco
Ferrari, Raquel Osorio. Clinical Oral Investigations, in press.
Introduction
Fiber posts are routinely used in dental practice for anchoring and
reinforce the prosthodontic restorations. Due to their passive retention into
root canal, the dislocation resistance of fiber posts is mainly ascribed to
the luting agents and cementation techniques (Bitter et al, 2006)
(D’Arcangelo et al, 2008). Resin-based luting materials are preferred for
fiber post cementation, as increase in post retention and higher fracture
resistance would be expected when compared to conventional cements
(Dietchsi et al, 2008) (Rosenstiel et al, 1998).
Self-adhesive cements represent a subgroup of resin cements and are
characterized by one-step, simple and standardized adhesive procedures.
These one-step cements do not require pre-conditioning of the post-space
walls. Due to the variability of the substrate, bonding to intra-radicular
dentin has been considered a challenge. Simplifying luting procedures
would be helpful in overcoming some technical problems observed with
multi-step cements systems (Radovic et al, 2008), such as the difficult
control of moisture and/or the chemical incompatibility between
simplified adhesives and dual-cured methacrylate-based resin cements
(Carilho et al, 2004) (Chersoni et al, 2005) (Pfeifer et al, 2003) (Tay et al,
2003).
Although high bond strength values are immediately desirable, the
cement should possess long-term satisfactory performances in order to be
145
clinically recommendable. The mouth is a complex and heterogeneous
environment, where a multitude of factors may simultaneously participate
to stress the adhesive interfaces and interfere with the longevity of the
restoration (Li et al, 2002). Oral conditions can be simulated in laboratory
enabling for a better understanding of the dental biomaterials properties
and possibly allow to predict the durability of the restorations (Breschi et
al, 2008) (Goracci et al, 2007). Thermocycling test is conventionally used
to simulate the thermal changes occurring in the oral cavity during eating,
drinking or breathing that may concur in stressing the adhesive interfaces
(Breschi et al, 2008) (Gale and Darvell, 1999) (Titley et al, 2003).
The bond strength of dental materials may be better assessed with
the push-out test. Push-out test has been considered appropriate for
measuring the bond strength inside the root canal, as the shear movements
are created parallel to the cement/dentin and cement/post interfaces and
seem to procure similar stresses to those occurring in clinical conditions
(Goracci et al, 2004) (Soares et al, 2008).
The present laboratory study was conducted to evaluate the effect of
thermocycling on the bond strength of translucent glass fiber posts luted
with different self-adhesive resin cements. The null hypothesis tested was
that thermocycling does not affect the bond strength of the three selfadhesive resin cements when luting fiber posts into root canals.
Materials and Methods
Specimen preparation
Thirty-six extracted, single-rooted human premolars stored in 0.5%
Chloramine T solution at 4° C were collected after the informed consent of
146
the donors was obtained. Exclusion criteria were presence of caries, cracks
or resorptions on the root. The crown of each tooth was removed 1 mm
above the CEJ by means of a slow-speed diamond saw (Isomet, Buehler,
Lake Bluff, IL, USA) under copious water cooling. Working length was
established at 1 mm from the root apex. Cleaning and shaping of the root
canal were performed with Protaper Ni-Ti rotatory instruments (size S1,
S2, S3; Dentsply Maillefer, Ballagues, Switzerland) following the crowndown technique. Irrigations with 5% sodium hypochlorite were performed
between the instrumentations. Root canal was filled with gutta-percha
cones (Coltène/Whaledent, Langenau, Germany) cemented with a resin
sealer (AH Plus Jet, Dentsply DeTrey, Konstanz, Germany) referring to
the lateral condensation technique. The canal access was sealed with a
temporary restorative material (Fuji VII, GC Corporation, Tokyo, Japan;
batch n° 0410221) and stored in a laboratory incubator (100% relative
humidity; 37° C). After 24 hours, the coronal seal was abraded by means
of #240 SiC paper under water cooling, and the gutta-percha was removed
with a pre-shaping drill (Dentsply DeTrey), leaving a 5 mm-long apical
seal. A 7 mm-deep post-space was prepared with a universal drill (3M
ESPE, Seefeld, Germany) to match the size of the co-respective epoxy
resin-based RelyX Fiber Post (#1; 3M ESPE; Lot: 02363200603). The
post was cut with a bur mounted on a water-coolant handpiece to the
selected coronal length. Three self-adhesive materials were employed for
fiber post cementation (n=12): 1) RelyX Unicem (3M ESPE); 2) G-Cem
(GC Corp, Tokyo, Japan); 3) Breeze (Pentron Clinical Technologies,
Wallingford, CT, USA).
147
Each material was handled according to manufacturer’s instructions.
Application modes, chemical composition and batch numbers of the
materials investigated are presented in Table 1.
Self-adhesive
cements
polymerized
in
a
dual-cure
mode.
Immediately, 2 s of light curing allowed to remove the extruding cement
with a spatula. After the first 5 min of auto-cure, during which the post
was seated to full depth in the prepared spaces using finger pressure,
additional 40 s of light polymerization through the top of the translucent
fiber post were performed (Astralis 7, Ivoclar-Vivadent, Schaan,
Liechtenstein; output: 500 mW/cm2). A core build-up was performed with
a glass-ionomer cement (Fuji IX; GC corp; Batch n°: 0703071). All
bonded specimens were stored for 1 month in a flower sponge slightly
wetted with deionised water in a laboratory stove at 37°C and relative
humidity.
Prior to push-out test, half of the specimens (n=18) were additionally
thermocycled for 5.000 cycles in deionized water from 5 to 50 °C. The
dwell time at each temperature was 30s in each bath; the transport time
between the water baths was 2s.
148
Table 1. Chemical composition, application modality and manufacturers instruction of the tested
materials.
Materia
Compositio
l
n
Rely X
Unicem
(3M ESPE,)
Batch n°:270644
G-Cem
(GC corp.)
Batch n°:0707051
Breeze
(Pentron
Clinical
Technologies)
Batch n°:161936
Powder: glass fillers,
silica, calcium
hydroxide, self-curing
initiators, pigments,
light-curing initiators,
substituted pyrimidine,
peroxy compound.
Liquid: methacrylated
phosphoric esters,
dimethacrylates, acetate,
stabilizers, self-curing
initiators, light-curing
initiators
UDMA;
phosphoric
acid ester monomer; 4META;
water;
dimethacrylates; silica
powder;
initiators/stabilizers;
fluoro-amino-silicate
glass
Mixture of BisGMA,
UDMA,
TEGDMA,
HEMA,
4-META
resins,
silane-treated
bariumborosilicate
glasses, silica with
initiators, stabilizers and
UV absorber, organic
and/or
inorganic
pigments, opacifiers.
Deliver
y
system
Capsule
and
Aplicap Elongation
Tip
Capsule
s
Paste/paste
dual
syringe with a
mixing tip
Instruction
s for use
Mix cement. Apply,
self-cure (5 min) and
light-cure (40s)
Mix cement. Apply,
self-cure (5 min) and
light-cure (40s)
Automix
cement.
Apply, self-cure (5
min) and light-cure
(40s)
Push-out bond strength test
The portion of each root containing the fiber post was sectioned into
four to six 1 mm-thick slices with a diamond saw (Isomet; thickness: 0.1
mm) under water cooling. The cylindrical plunger of the testing machine
(Triax 50, Controls S.P.A, Milan, Italy) was forced to dislodge, via an
149
apical-coronal direction, each inverted, truncated fiber post from the root
dentin. A load (cross-head speed: 0.5 mm/min until failure) was then
applied to the post surface that resulted in shear stresses along the
cement/dentin – cement/post interfaces. The retentive strength of the post
fragment (MPa) was calculated by dividing the load at failure (Newton) by
the interfacial area of the post segment (SL). The formula used for
measuring the tronco-conical area as follows:
SL = π (R+r) [(h2+ (R-r)2]0.5
In which π was equal to 3.14, R and r were the coronal and the apical
post radius respectively, and h the root slice thickness. The diameters of
the post and the thickness of the slice were individually measured using a
digital caliper with 0.01 mm accuracy.
Failure modes were evaluated by a single operator under a
stereomicroscope (Olympus SZ-CTV, Olympus, Tokyo, Japan) at 40x
magnification (Fig. 1) and classified as cohesive (within the cement, C),
adhesive (between the post and the cement, AP, or at the cement/root
dentin level, AD) or mixed (adhesive and cohesive fractures occurred
simultaneously, M) (Fig. 1).
Statistical analysis
The normal and equal distributions of the push-out bond strength
data were first checked and verified by the Kolmogorov-Smirnov and
Levene’s test respectively.
A 2-way ANOVA was executed to determine the effect of the type
of cement, thermocycling and interactions (p<0.05). Mean bond strengths
of the three cements were analyzed with the Tukey test for post-hoc
multiple comparisons (p<0.05). Calculations were handled by the SPSS
15.0 software (SPSS Inc.; Chicago, IL, USA).
150
Results
Bond strength was significantly influenced by the luting material
(F=14.640; p=0.00) and thermocycling (F=18.205; p=0.00), interactions
were also significant (F=3.836; p=0.01). Mean push-out bond strengths
(SD) of the tested cements (MPa) prior and after thermal cycling are
shown in Table 2.
Initially, push-out bond strengths of RelyX Unicem and Breeze were
statistically comparable and higher than those exhibited by G-Cem.
Thermocycling did not affect the bond strengths of RelyX Unicem and
Breeze. After the thermal challenge, increased push-out values were
registered for G-Cem when compared to the initial group and no
differences were then found among the tested groups.
The most frequently recorded modes of failure were adhesives at the
cement/dentin interfaces (Table 3). Debonded specimens between cement
and fiber posts were also recorded both in the initial and in the
thermocycled groups (Fig. 1). Cohesive failures within the cement were
only registered for RelyX Unicem prior to thermocycling. Mixed failures
were observed for RelyX Unicem and G-Cem before being thermally
challenged.
151
Table 2. Mean bond strength (SD) values (MPa) and post-hoc
comparisons results.
Material
Initial
TC
RelyX Unicem
10.27(2.18) A
13.66(8.23) A
G-Cem
6.78(2.57) B
10.0(4.34) A*
Breeze
10.31(4.60) A
9.92(6.33) A
Different capital letters in columns and asterisks in rows indicate differences (p<0.05). TC:
thermocycling.
Table 3. Percentage of failure registered in each experimental group.
Initial
TC
Experimental groups
AD
AP
C
M
AD
AP
C
M
RelyX Unicem
69%
19%
6%
6%
62%
21%
0%
17%
G-Cem
61%
15%
0%
24%
97%
3%
0%
0%
Breeze
54%
46%
0%
0%
83%
17%
0%
0%
AD: adhesive failure at the dentin interface; AP: adhesive failure between cement and post; C:
cohesive failure within the cement; M: mixed failure (a combination of the above mentioned
modes). TC: thermocycled group.
152
Discussion
The null hypothesis has to be rejected as bond strengths were
different for the tested cements and thermocycling did affect these values.
Self-adhesive cements were introduced to simplify the luting
procedures of indirect restorations and shorten chair time. One clinical
study, reported that RelyX Unicem worked as efficiently as a zinc
phosphate cement during a period of 138 days (Behr et al, 2008).
However, only few investigations dealt with the resistance of simplified
cements to thermal stresses, and contrasting results were noticed.
It was speculated that the thermal stress occurring during the
laboratory test would enhance the chemical polymerization of the
materials, promoting their complete setting reactions (Bitter et al, 2006)
(Piwowarczyk et al, 2006) (Reich et al, 2005). In the present study, no
differences in push-out values were encountered for RelyX Unicem and
Breeze before or after being thermally challenged. An increase in bond
strength was previously reported for RelyX Unicem when used for luting
fiber posts or ceramic restorations (Piwowarczyk et al, 2006) (Reich et al,
2005). Contrary to these investigations, in the present study the roots were
not embedded in acrylic resins and no isolation was created around the
bonded interfaces. The direct exposure of the root to the different
temperatures may have promoted weak adhesive-dentin interfaces
counting for the differences registered between the investigations. Some
questions arise on the degree of monomer conversion of self-adhesive
cements when used in an auto-cure mode, an incomplete polymerization is
expected and it will jeopardize bond strength (Kumbuloglu et al, 2004)
(Vrochari et al, 2009). If so, dual-curing self-adhesive cements have
153
become imperative for achieving reliable bonding. Future studies are
warranted to deeply investigate on this topic.
Scarce information are present in literature regarding the bonding
ability of Breeze as fiber post cementing agent. When compared to another
self-adhesive cement and a glass-ionomer cement Breeze showed the
highest dislodgement force after storage in water for 30 days (Elsayed et
al, 2009). Breeze is composed by a mixture of hydrophilic components
(i.e. BisGMA and HEMA) and hydrophobic monomers (i.e. TEGDMA).
The latter molecule would furnish the material hydrophobic characteristics
necessary to withstand to the moisture condition of dentin and prevent an
excessive water sorption that would jeopardize the polymerization reaction
of the material. However, further studies are required to well define the
bonding performance of Breeze.
G-Cem have previously showed the worse push-out values when
used for luting fiber posts in comparison to RelyX Unicem and multi-step
resin cements (Zicari et al, 2008). Although the auto-adhesion mechanism
of G-Cem follows a glass-ionomer technology (G-Cem technical
information, GC corp.), its high viscosity has been responsible of the
scarce interaction with the adhesive substrates (Zicari et al, 2008).
However, bond strength of G-Cem increased after thermal challenging.
Thermal changes will cause expansion/contraction stresses within the
material (El Araby and Talic, 2007) (Titley et al, 2003), what may affect
the adhesive stability; but the cement expansion will also create frictions
along the root canals that are thought to improve its mechanical retention
(Cury et al, 2006). After setting, G-Cem showed a porous appearance at
the adhesive interface (Cantoro et al, 2009). The pores and bubbles would
function as stresses-absorbers that would prevent the premature
154
degradation of the adhesive interfaces (Monticelli et al, 2007). It remains
to be proved if prolonged expansion/contraction phenomena would result
in crack formations within the cement bulk hence diminishing the
mechanical properties of the material and if the pores present into the
material would resist to prolonged cycles and mechanical occlusal loading
and their resistance to degradation when submitted to chemical solutions
(i.e. sodium hypochlorite).
Although in vivo studies are the ultimate testing stages, laboratory
tests and aging simulations are important sources for reproducing intraoral conditions (Alani and Toh, 1997) (Amaral et al, 2007) (Goracci et al,
2004). Thermocycling test is conventionally used to simulate the thermal
changes and water exposure that may occur in the oral cavity during
eating, drinking or even breathing (Gale and Darvell, 1999). The ISO TR
11450 (ISO reports) reports that 500 thermocycles in water (5 and 55°C),
is an appropriate method to test thermal stability of a dental material. To
date, concerns still arise on the ability of the test to simulate intra-oral
ageing. In the present study, specimens were thermocycled for 5.000
times, although increasing the number of cycles would be desirable to
evaluate eventually pronounced differences in a longer period of time.
The importance of using the cement/post combination recommended
by each manufacturer has been previously highlighted (Kececi et al, 2008)
(Radovic et al, 2008). Glass-, quartz-, zirconium- and/or titanium- posts
differ in terms of structure, composition and mechanical properties that
can influence their bonding mechanism as well as affect their responses to
chemo/mechanical treatments. In the present investigation, only one type
of post was used, that it is made of glass fibers (60-70 vol%) embedded in
an epoxy resin (RelyX Fiber Post technical pamphlet, 3M ESPE).
155
Although no differences were found between cements after thermocycling,
the bonding performance of self-adhesive cements to others fiber posts
differently branded should also be evaluated.
The most frequently registered mode of failures were adhesives
between cement and dentin, followed by adhesive at the cement/post
interface both prior and after thermocycling (Table 4). The self-adhesive
cement-dentin joint represents the weaker point of the one-step cements.
Although self-adhesive cements do not require any pre-treatment of the
bonding substrate, their retention was increased once the post-space cavity
was roughened, resulting in micro-mechanical grooves formations were
the cement could flow and establish an improved bonding (Balbosh et al,
2005). Doubts also exist on the efficacy of pre-treating fiber posts in the
attempt of increase the retention of the auto-adhesive cements/fiber post
bonds, such as with silane agents (Bitter et al, 2007). Due to the limited
chemical interaction established between self-adhesive cements and fiber
posts, chemo-mechanical post surface treatments could be proposed to
increase the surface area available for bonding and enhance microretentions (Wrbas et al, 2007).
In general, bond strength of dual-cure self-adhesive luting agents is
not compromised by physiologic thermal stresses. A combination of
chemical adhesion and mechanical retention seemed to characterize the
adhesion mechanism of these simplified cements although further studies
are desirable to define the overall bonding process of the different selfadhesive luting agents.
156
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Carrilho MRO, Carvalho RM, Tay FR, Pashley DH. Effects of
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Chersoni S, Acquaviva GL, Prati C, Ferrari M, Grandini S, Pahley
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Cury AH, Goracci C, de Lima Navarro MF, Carvalho RM, Sadek
FT, Tay FR, Ferrari M. Effect of hygroscopic expansion on the push-out
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D’Arcangelo C, D’Amario M, Vadini M, Zazzeroni S, De Angelis F,
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Dietschi D, Duc O, Krejci I, Sadan A. Biomechanical considerations
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Goracci C, Grandini S, Bossù M, Bertelli E, Ferrari M. Laboratory
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Goracci C, Tavares AU, Fabianelli A, Monticelli F, Raffaelli O,
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161
Chapter 6
6.1 Post surface treatments for improving the adhesive bonds
Although the adhesion into root canal may represent the weakest
point of the restoration (Ferrari et al, 2000a) (Ferrari et al, 2002),
decementation at the cement/post level may compromise the final outcome
(Ferrari et al, 200b) (Monticelli et al, 2003). The occurrence of post
debondings does not have to be considered an irreversible failure, since an
advantage of using fiber post is that they can easily be replaced. However,
this event would be time-consuming and not always accepted by the
patients.
The search for improved adhesions of resin cements to fiber post has
ever forced investigators to experiment new methodologies that can
enhance the resin cement/fiber post interfacial strength. These consist in
different chemical and mechanical treatments (Goracci et al, 2005)
(Monticelli et al, 2006a) (Monticelli et al, 2006b) (Sahafi et al, 2004)
intended to modify the post matrix composition and morphology as well as
to increase the surface energy of dental posts (Asmussen et al, 2005) (Le
Bell et al, 2004). Although silane application has been recommended for
enhancing adhesion (Aksornmuang et al, 2004) (Perdigao et al, 2006)
thank to the chemical bridges it can establish, others chemo/mechanical
post surface treatments have been proposed in order to strengthen the
bonds. These conditioning approaches, can be performed solely (i.e. silane
application) or in combinations (i.e. sandblasting plus silane application)
(Magni et al, 2007). These treatments are efficient for improving the
union between methacrylate resin based cements and epoxy-resin based
fiber posts that are chemically incompatible. The rationale rely on the
removal/dissolution of the superficial and inter-fiber epoxy-matrix, on the
162
exposure of the underlying glass fibers that can be then activated with
silane or adhesive solutions. However, attention should be paid to the
methodology adopted for conditioning fiber post: an excessive diameter of
air-bone particle, a limited distance between the sandblasting device and
the post the high pressure are all possible factors that may damage the
fiber posts (Monticelli et al, 2008) (Sahafi et al, 2004). Methods already
adopted for treating ceramic crowns were applied to fiber post as well,
such as hydrofluoric acid. However, this treatment was too aggressive for
the post fibers thus affecting the post’s integrity (Vano et al, 2006).
Others laboratory and industrial techniques have been proposed over the
years to improve the bonding potential of fiber posts (Monticelli et al,
2006a) (Monticelli et al, 2006b).
In the following trials it was of interest to examine the effects that
different post conditioning approach could have on its topographic
appearance as well as to distinguish the treatments that could be proposed
in order to obtain reliable and safer bonds. It was also taken into
consideration whether and to what extent the bonding potential of selfadhesive cements would be reinforced after the post surface treatments.
Different in vitro studies were presented: in the first, two combined
microscopic methodologies (confocal microscopy and atomic force
microscopy) were used to analyze and determine the post surface
roughness after the different conditioning procedures and whether these
treatments were able to dissolve the incompatible epoxy-matrix without
damaging the glass fibers. In the second study, a push-out test and a
scanning electron microscopy evaluation were performed to assess the
retentive strength of self-adhesive resin cements to pre-treated epoxy-resin
based fiber posts.
163
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165
6.2 Surface roughness analysis of fiber post conditioning processes.
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Introduction
Considerable attention has been paid to the clinical application of
fiber posts. Reliable bonding can be achieved when post, luting material
and dentin achieve good adhesion, thus forming a ―mono-block‖ unit
(Schwartz and Robbins, 2004). Most of the studies of fiber posts bonded
to radicular dentin have stated that the majority of failures occurred
between the post and the cement (Baldissara et al, 2006) (Perdigao et al,
2006). Recent investigations have been focused on improving this
adhesive interface in attempt to enhance the durability of final restorations
(Valandro et al, 2006).
The benefit of applying silane-coupling agents as adhesion
promoters has been reported (Aksornmuang et al, 2004) (Aksornmuang et
al, 2006) (Goracci et al, 2006). However, the post/composite joint still
remains relatively weak. Coupling of conventional epoxy-resin-based fiber
posts to dental composites is hampered by the absence of chemical union
between the epoxy resinous matrix and methacrylate-based resins
(Monticelli et al, 2006a).
Different post surface treatments may improve adhesion of posts to
composite resins (Balbosh and Kern, 2006) (Monticelli et al, 2006a).
These are chemical and mechanical treatments intended to roughen the
post surface, generating mechanical interlocks between the post and resin
166
cements. They may include the use of etching solutions as well as physical
roughen procedures, such as sandblasting (Balbosh and Kern, 2006)
(Monticelli et al, 2006a) (Monticelli et al, 2006b).
Previously, conditioned surfaces have been analyzed by scanning
electron microscope (SEM) (Monticelli et al, 2006b) (Vano et al, 2006).
However, atomic force microscopy (AFM) may represent an alternative
methodology with some additional advantages. It can works in air,
requires little or no sample preparation, and provide high-resolution
imaging of 3-D surface topography (Marshall et al, 1995). A confocal
imaging profiler is routinely applied to analyze surface texture, measuring
the actual profile and standard numerical roughness parameters that can be
calculated from the profile itself. It has been widely used for assessing the
surface topography of dental implants (Hallgren et al, 2001).
Therefore, the aim of this study was to evaluate the surface
topography and changes in average roughness (Ra) provided by different
fiber post surface treatments through the combined use of atomic force
(AFM) and confocal microscopy. The null hypothesis tested was that
different surface treatments would neither modify the post’s surface
morphology nor affect its individual components (fiber/matrix).
Materials and Methods
Forty translucent quartz fiber posts #3 with a maximum diameter of
2.14 mm (DT Light Post, batch #120US0401A; RTD, St Egrève, France)
were used for the study. The posts are made of unidirectional pre-tensed
quartz fibers (60% vol) bound in an epoxy resin matrix (40% vol). Posts
were divided into 8 groups (n=5) according to the surface pre-treatment
performed: Group 1, no treatment; Group 2, 10% hydrogen peroxide
167
(H2O2) for 20 min; Group 3, 30% hydrogen peroxide (H2O2) for 10 min;
Group 4, 21% sodium chloride (NaOCH2CH2) for 20 min; Group 5,
etching with potassium permanganate (KM2O4); Group 6, etching with 4%
hydrofluoric acid for 1 min; Group 7, sandblasting; Group 8, silicate/silane
coating (DT Light SL post, batch #05/65; VDW GmbH, Munich,
Germany).
Posts from Groups 2 and 3 were immersed in hydrogen peroxide
solutions (for 20 and 10 min, respectively) (Panreac Quimica SR,
Barcelona, Spain) at room temperature (RT) and rinsed with de-ionized
water (3 min). Fiber posts in Group 4 were etched with 21 wt% sodium
ethoxide solution (Sigma-Aldrich Chem., GmbH, Steinheim, Germany) in
ethanol (20 min) at RT, rinsed with pure ethanol and 50% ethanol in deionized water, and finally in de-ionized water to reach a stable pH of 7 (5
min for each cleaning bath).
The etching for Group 5 was performed in three consecutive steps:
1) immersion in a conditioning solution (60 vol% of methyl-pyrrolidone in
de-ionized water) for 3 min at 50-60°C (E-K Hole Cleaner, Elkem, Torino,
Italy); 2) etching in an alkaline potassium permanganate solution (20 vol%
in de-ionized water, pH 12-13) (E-K Hole Oxidizer, Elkem) for 10 min at
70-80°C; and 3) immersion in a neutralizing bath containing dilute
sulphuric acid (10 vol% in de-ionized water) (E-K Hole Reducer, Elkem)
for 5 min at 40-50°C to reduce and neutralize the excess permanganate
and clean the post surface (Monticelli et al, 2006b).
Posts in Groups 6 were immersed in 4% hydrofluoric acid solution
(Panreac Quimica SR) for 1 min at RT and then extensively rinsed with
de-ionized water. Samples of Group 7 were sandblasted (Rocatec Pre, 3M
ESPE, Seefeld, Germany) for 5 s at 2.8 bar. The tip of the sandblasting
168
device was held perpendicularly to the post at a distance of 1 cm. During
the procedure, the post was rotated so that the aluminium oxide particles
(110 um) would be blasted on the entire surface. Posts in Group 8 had
already been coated with silicate and silane by the manufacturer; a
patented protective layer ensured that the superficial coating was not
contaminated or deactivated.
Each fiber post was then cut longitudinally with a slow-speed
diamond saw under water cooling (Isomet 4000; Buheler, Lake Bluff, IL,
USA), so that the post was divided into two equal halves. Posts of Groups
1 and 7 were ultrasonically cleaned in de-ionized water (10 min), rinsed in
96% ethanol, and dried with an oil-free air stream. Posts from Group 8
were gently air-dried, to avoid any possible alteration of the coating.
Confocal microscopy
One half of each treated fiber post was evaluated under a confocal
imaging profiler (Eclipse L150 Sensofar, Nikon, Tokyo, Japan), with a
X50/0.80 numerical aperture and an extra-long working distance dry
objective (Nikon), for the collection of reference images of the post
surface. Images were captured by a CCD camera (Nikon) and
reconstructed with a computer software program (plµ Confocal Imaging
Profiler). Average surface roughness (Ra) recorded for each treated
post (10 measurements each experimental group) was quantitatively
expressed as a numerical value (in microns) and a graph of the profile.
Atomic Force Microscope (AFM) evaluation
The second half of each sample was evaluate by atomic force
microscopy (AFM, Multimode Nanoscope IIIa, Digital Instruments,
169
Veeco Metrology group, Santa Barbara, CA, USA). Images were taken in
air. The tapping mode was performed with a 1-10 Ohm-Cm phosphorousdoped (n) Si tip (at 50µ). Changes in vertical position provided the height
of the images, registered as bright and dark regions. The tip sample ―tap‖
was maintained stable through constant oscillation aplitude (set-point
amplitude). Fields of view at 50X50 µm scan size were considered for
each post at a data scale of 1504 µ and recorded with a slow scan rate (0.1
Hz). A single operator analyzed the average surface roughness (Ra) of the
matrix/quartz fiber post after different surface treatments, expressing it as
a numeric value (in nanometers) with specific software (Nanoscope
V530R35R). Five measurements were performed for each pre-treated post,
on both the epoxy matrix and quartz fibers, with a standardized
rectangular spot (1.56X1.37 µm). Regarding the DT Light SL post, it was
not possible to measure fiber roughness, since they were completely
covered by the superficial coating.
Statistical analysis
Surface roughness data and matrix/fiber average roughness values
were statistically analyzed with one-way Analysis of Variance. The
Student-Newman-Keuls test was used for post hoc comparisons. The level
of significance was set at p<0.05.
Results
Post surface average roughness (Ra) resulting fro digital images
recorded by confocal microscopy (Figs. 1A-1H) revealed that chemomechanical conditioning treatments
significantly modified surface
roughness (p<0.001) (Table 1). Etching with HF, sandblasting and
170
potassium permanganate and sodium ethoxide treatments resulted in a
significant improvement in (Ra). 3-D cnfocal profiler image revealed a
variation in post surface topography with micro retentive space formation
and fiber exposure.
Changes in average roughness (Ra) of the epoxy resin matrix were
recorded by AFM analysis after all post surface pre-treatments (Table 2).
HF attained the highest Ra value (Fig. 2A). After treatment with potassium
permanganate, the resulting matrix was smoother (Fig. 2B). In the DT
Light SL Post, quartz fibers were enshrouded by the silicate/silane coating
(Fig. 2C). A significant increase in roughness of the superficial quartz
fiber after treatment with hydrofluoric acid was detected (Fig. 2A). Fibers
appeared to be fracture-free, with no evident signs of degradation in the
other experimental groups.
Table 1. Mean (SD) of surface roughness values recorded with a confocal image profiler after
different post surface pre-treatments. Same alphabetical letters indicate groups that are statistically
similar (p<0.05).
Superficial pre-treatment
Mean Roughness (SD, µm)
Hydrofluoric acid (4%)
3.929(1.14) A
Sandblasting (Rocatec Pre)
4.042(1.04) A
Potassium permanganate
3.210(0,73) AC
Sodium ethoxide
3.149(0.81) AC
Hydrogen peroxide (30%)
2.538(0.36) BC
Hydrogen peroxide (10%)
2.824(0.58) BC
Silicate/silane coating (DT Light SL Post)
2.539(0.43) BC
Control (no treatment)
2.207(0.56) BC
171
Fig 1. Confocal profiler 3D images of the post surface after different chemo-mechanical pre-treatments. A) Control (DT Light
Post). B) 30% hydrogen peroxide. C) 10% hydrogen peroxide. D) Silicate/silane coating (DT Light SL Post). E) Hydrofluoric
acid. F) Potassium permanganate. G) Sandblasting (Rocatec Pre). H) Sodium ethoxide. The differences in colors between yellow
and red represent the ―peak‖ and the ―valley‖ of the surface. A partial removal of the external layer of epoxy resin after
conditioning treatments determined the partial exposition of the fibers. The oxidative etching procedure exerted their function
mainly via a dissolution process of the resin matrix, leaving the quartz fiber undamaged. A more aggressive approach was
determined by the application of HF. DT Light SL Posts were completely smooth, due to the superficial coating responsible for
their chemical adherence to resin composites.
172
Table 2. Mean (SD) average surface roughness values (Ra)of the resinous matrix and the fibers
recorded under AFM after different post-surface pre-treatments. Same aplphabetical letters indicate
groups that are statistically similar (p<0.05).
Superficial pre-treatment
Hydrofluoric acid (4%)
Sandblasting (Rocatec Pre)
Hydrogen peroxide (30%)
Sodium ethoxide
Hydrogen peroxide (10%)
Control (no treatment)
Potassium permanganate
Silicate/silane coating (DT
Light SL Post)
Matrix average
roughness (SD, nm)
75.15(14.3) A
36.03(14.81) B
30.66(7.96) B
37.32(15.3) B
28.23(1.6) B
23.3(14.3) BC
13.64(7.9) CD
Fiber average
roughness (SD, nm)
58.15(11.5) A
16.68(12.9) B
9.09(1.7) B
12.09(2.8) B
8.31(5.2) B
4.86(1.9) B
6.3(3.7) B
6.61(2.3) D
---
173
Fig.2. AFM images of treated quartz
fiber post (50 x 50 µ). The squares
(1.56 x 1.37 µm) show the area used
for roughness measurements at the
resin matrix (grey) and the fiber
(white). (A) Hydrofluoric acid. The
etching procedure was able to
dissolve the resin matrix, but the
effects were too corrosive, with
exposed quartz fibers resulting in
superficial blister formations; (B)
Potassium permanganate. An intact
fiber with no sign of damage is
evident, and the matrix appeared
smoother than with other treatments,
most likely as a consequence of the
resin-swelling step that preceded the
etching
procedure.
(C)
Silicate/silane industrial coating (DT
Light SL Post). No quartz fibers are
exposed on the post surface.
174
Discussion
The results of this study revealed an increase in fiber post surface
roughness after chemo-mechanical conditioning. The etching procedures
reacted mainly with the epoxy-resin matrix, most likely by dissolution.
Thus, the null hypothesis was rejected.
Most of the study on fiber post morphology have been performed
with scanning electron microscope (SEM), providing only qualitatively
information (Monticelli et al, 2006b) (Vano et al, 2006).
AFM has been widely used to investigate the structural changes
determined by etching procedures on enamel and dentin (Marshall et al,
1997) (Hegedüs et al, 1999) (Saeki et al, 2001) (Lippert et al, 2004), or for
evaluating different biomaterials (Cross et al, 2005). Together with the use
of a confocal imaging profiler, this represents an effective methodology
for analyzing not only a curved surface, like that of fiber posts, but also its
modification after conditioning with chemical of physical agents. The
average surface roughness can be qualitatively determined and converted
into a numerical reading of the surface topography (Marshall et al, 1997)
(Hallgren et al, 2001). Moreover, AFM allowed for the quantification of
treatment effectiveness on the post’s individual components (matrix and
fibers), expressing it as a nanometric increase in roughness.
The concept of conditioning artificial substrates to enhance bonding
has precedents in dentistry, e.g. the etching of Maryland bridges
(Thompson et al, 1983) (Thompson et al, 1984) or feldsphatic porcelain
restorations (Horn, 1983).
The rationale for conditioning the fiber posts relies on the purpose of
removing a surface layer of epoxy resin, rendering more quartz fibers
175
available for silanization, and improving the fiber post surface bonding
area. The etching potential of the alkaline chemicals used depends on its
capacity to partially dissolve the epoxy resin matrix through a mechanism
of substrate oxidation (Baskin et al, 1979) (Kirman et al, 1998) (Brorson,
2001). The spaces between the fibers provide site for micro-mechanical
retention of resin composites. Results of the present investigation
confirmed the benefit of some chemo-mechanical treatments, also
considering the previously reported bond strength results obtained at the
fiber/composite interface (Monticelli et al, 2006b).
Sandblasting is commonly used for treating ceramic and composites,
or as a part of the tribochemical silica-coating process (Saunders, 1990)
(Borges et al, 2003). The efficacy of blasting zirconia and fiber posts with
silica oxide (CoJet System, Praxair, Inc., Danbury, CT, USA) has been
tested (Sahafi et al, 2003) (Sahafi et al, 2004a) (Sahafi et al, 2004b).
Despite the satisfactory bond strengths achieved, the treatment was
considered too aggressive for fiber posts, because of the risk of
significantly modifyingtheir shape and fit within the root canals (Sahafi et
al, 2004a). In this study, a significant increase in post surface roughness
has been recorded after sandblasting (Rocatec Pre, 3M ESPE). The
treatment was effective on the resinous matrix. However, no apparent
signs of deterioration of the post were detectable. Dimensions of the
aluminum oxide particles, as well as the time of application and distance,
may have influenced these results.
Hydrofluoric acid has recently been proposed for etching glass fiber
posts (Vano et al, 2006). The acid is able to ―activate‖ the post surface,
allowing for the formation of micro-retentive spaces. However, the texture
of the exposed quartz fibers was more irregular than with other treatments,
176
with blister formation. As a consequence of the extremely corrosive effect
of hydrofluoric acid on the glass phase (Addison and Fleming, 2004)
(Vano et al, 2006), the technique may produce substancial damages to
fiber post substructure, especially when used with extended application
time.Thus, its application is discouraged.
Currently, the dental market offers poststhat have already been precoated with combined silicate/silane layers. No fibers are exposed on the
surface of SL post, which appears relatively smooth. The adhesion
mechanism is essentially based on the chemical interaction of the coating
with the resin composite/luting cement. The industrial coating appears
promising for simplifying the clinical procedures during post placement.
Further investigations are needed to assess if post surface pre-treatments
with chemical and/or mechanical agents can withstand longevity testing
and influence the long-term clinical effectiveness.
In conclusion, atomic and confocal microscopy represents an
effective method for evaluating fiber posts surface topography. Etching
with potassium permanganate or sodium ethoxide increases surface
roughness through partial removal of the epoxy resin matrix and improve
the surface area available for adhesion by creating micro-retentive spaces.
The choice of aggressive conditioning chemicals, such as hydrofluoric
acid, should be avoided to prevent any damage to quartz fibers.
177
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Aksornmuang J, Nakajima M, Foxton RM, Tagami J. Regional bond
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Balbosh A, Kern M. Effect of surface treatment on retention of glass
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181
6.3 Effects of post surface treatments on bond strength of selfadhesive cements
Claudia Mazzitelli, Federica Papacchini, Francesca Monticelli, Manuel
Toledano, Marco Ferrari. American Journal of Dentistry
Introduction
Fiber posts gained popularity over the years for the restoration of
endodontically treated teeth with massive coronal destruction (Cagidiaco
et al, 2007) (Ferrari et al, 2007). In the attempt to predict the clinical
success of the post-restored teeth, great attention has been focused on the
uniformity of the root dentin/cement/post joints that should form a
―monoblock‖ unit (Schwartz and Robbins, 2004) (Monticelli et al, 2008a).
However, decementations at the cement/post site bonds have frequently
been observed, possibly compromising the longevity of the final
restorations (Ferrari et al, 2007b) (Baldissarra et al, 2006). The variability
of the dental substrate and the different chemical composition between
most of the cement/post systems, make hard to establish a unique bonding
mechanism into root canals (Perdigao et al, 2006) (Monticelli et al, 2006)
(Aksornmuang et al, 2004) (Tay and Pashley, 2007).
Methacrylate resin-based luting agents showed good mechanical
properties and are increasingly used for the cementation of fiber posts.
Frequently, posts are made of fibers (i.e. glass, quartz) embedded in an
epoxy resin matrix that is chemically incompatible with the methacrylate
resin-based cements (Monticelli et al, 2008a). Chemo/mechanical post
surface treatments have been proposed to enhance the adhesion with the
resin cements through the removal/dissolution of the incompatible epoxy
resin matrix and the exposure of the underneath fibers, that can be then
182
activated by silanization establishing more suitable bonds with the luting
agent (Monticelli et al, 2008b) (Vano et al, 2006). An increase in the post
surface roughness has recently been assessed after selected surface
treatments; the micro-spaces created along with the post surface are
intended to increase the surface are available for bonding and to facilitate
the overall retentive strength of resin cements (Mazzitelli et al, 2008).
Among the luting materials available for the cementation of fiber posts,
self-adhesive resin composite cements are the least introduced category
designed for ensuring simpler and standardized bonding procedures
(Toman et al, 2009) (Bateman et al, 2005). Although their applications
rely on a single clinical step, the chemo/mechanical post surface
treatments on self-adhesive cements bonding performances have been
investigated would ideally improve the self-adhesive cements bonding
performances, as the establishment of stringer mechanical retentions
would be desirable to reinforce the self-adhesive cement/fiber post joints
(Hayashi et al, 2008) (Wrbas et al, 2007) (Bitter et al, 2007).
The purpose of this study was to determine the push-out bond
strength of two self-adhesive resin cements to epoxy resin-based quartz
fiber posts after different fiber conditioning treatments. The null
hypothesis tested was that post surface treatments does not influence the
bond strengths of self-adhesive resin cements.
Materials and Methods
Fifty single-rooted human premolars, extracted for periodontal or
orthodontic reasons, were used for the study after receiving the informed
consent of the donors. Exclusion criteria were presence of caries, cracks or
root resorptions.
183
The crown of each tooth was removed 1 mm above the CEJ by
means of a slow-speed diamond wheela under copious water cooling.
Working length was established at 1 mm from the root apex. Cleaning and
shaping of the root canal were performed with Protaper Ni-Ti rotator
instruments (size S1, S2, S3)b following the crown-down technique.
Irrigations with 5% sodium hypochlorite were performed between
instrumentations. Gutta-percha conesc were used for filling the root canal
and cemented with an epoxy-resin based sealerd according to the lateral
condensation technique. Roots were coronally sealed with a glass-ionomer
cemente (LOT: 0410221) and stored in a laboratory incubator at 37°C and
100% relative humidity. After 24 hours, the temporary seal was abraded
by means of #240 SiC paper under water cooling, and the coronal guttapercha was removed with a pre-shaping drillf, leaving a 5 mm-long apical
seal. A 7 mm-deep post space was prepared with a universal drill to match
the size of the co-respective DT Light Post #3g (maximum diameter: 2.14
mm). The posts are made of unidirectional pre-tensed quartz fibers bound
in an epoxy resin matrix. Fiber posts were divided in 5 groups (n=10)
according to the surface pre-treatment performed: Group 1. Silanization: a
single-component, pre-hydrolized silanizing agenth (Batch n°: H34023)
was applied with a microbrush on the entire post surface for 60 s and then
gently air-dried. Group 2. Etching: posts were immersed in 10% hydrogen
peroxide solutioni for 20 min at room temperature and then rinsed with
deionized water for 3 min. Group 3. Sandblasting: the entire post surface
was blasted with aluminum oxide particles (110 µm)j for 5 sec at 2.8 bar.
The tip of the sandblasting device was held perpendicularly to the post
surface at a distance of 1 cm. Group 4. Industrially silicate/silane coatingk.
184
A patented protective layer ensured that the superficial coating was not
contaminated or deactivated during its handling. Group 5. No treatment.
Prior to the luting procedures, each post was cleaned in an ultrasonic
device for 10 min, immersed in 95% ethanol solution and air-dried.
Two self-adhesive composite cements were used for luting fiber
posts into root canals: 1) RelyX Unicem unidosel; 2) Max-Cemm. The
materials were handled following manufacturer’s instructions. Application
modes, chemical compositions and batch numbers of the investigated
materials are presented in Table 1. After capsule activation, RelyX
Unicem was injected into the post space by means of a specific elongating
tip directly connected to the capsule. Base and catalyst (1:1) of Max-Cem
were dispensed onto a glass pad and carefully mixed until obtaining an
homogeneous paste. The material was inserted with a lentulo spiral into
the post-space and was applied on the entire post surface. Each post was
inserted into the canal and maintained under pressure until the complete
setting of the materials. Two seconds of light irradiation allowed to easily
remove the cement excesses. Self-adhesive cements were polymerized in a
dual-curing mode. After the first 5 min of auto-cure, additional 40 s of
light polymerization through the translucent fiber post were performed
(Astralis 7, output: 600 mW/cm2)n. A core build-up was created with
CoreX resin compositef (batch n°: 0703000080) around the post.
Specimens were then stored in a laboratory incubator for 1 month at 37°C
and relative humidity in order to simulate a clinical hydration state.
Push-out bond strength test
The portion of the root containing the fiber post was subsequently
sectioned into four-to-six 1 mm-thick slices with a diamond saw (Isomet)
185
under water cooling. The cylindrical plunger of the testing machine (Triax
50, Controls S.P.A, Milan, Italy) was forced to dislodge, via an apicalcoronal direction, each inverted, truncated fiber post from the root dentin.
A load (cross-head speed: 0.5 mm/min until failure) was then applied to
the post surface that resulted in shear stresses along the cement/dentin –
cement/post interfaces. The retentive strength of the post fragment (MPa)
was calculated by dividing the load at failure (Newton) by the interfacial
area of the post segment (SL). The formula used for measuring the troncoconical area was so expressed: SL = π (R+r) [(h2+ (R-r)2] 0.5
in which π was equal to 3.14, R and r were the coronal and the apical
post radius respectively, and h the root slice thickness. The diameters of
the post and the thickness of the slice were individually measured using a
digital caliper with 0.01 mm accuracy.
Failure modes were evaluated by a single operator under an optical
microscope (Olympus SZ-CTV, Olympus, Tokyo, Japan) at 40x
magnification and classified as follows: cohesive within the cement (C),
adhesive between the post and the cement (AP), adhesive at the
cement/radicular dentin level (AD), mixed, adhesive and cohesive
decementations occurred simultaneously (M).
Scanning electron microscopy evaluation (SEM)
Four stressed-to-failure beams from each group were used for
scanning electron microscopy (SEM) evaluation. Each beam was
conditioned with ascending ethanol solution (from 50% up to 90%),
mounted on a metal stub, gold-sputtered (Polaron Range SC 7620,
Quorum Technology, Newhaven, UK) and evaluated under an SEM (JSM6060LV, Jeol, Tokyo, Japan) at different magnifications.
186
Table 1. Chemical composition, manufacturer, batch numbers and application mode of the
materials tested in the study.
Materials
Compositions
Cement Application
RelyX Unicem
(3M ESPE)
Batch n°: 270644
Powder: glass fillers, silica, calcium
hydroxide, self-curing initiators,
pigments, light-curing initiators,
substituted pyrimidine, peroxy
compound. Liquid: methacrylated
phosphoric esters, dimethacrylates,
acetate, stabilizers, self-curing
initiators, light-curing initiators
MaxCem
(Kerr Corp.)
Batch n°: 452187
Base: Uretanedymethacrylate,
Camphoroquinone,
Fluoroaluminosilicate, others.
Catalyst: Bis-GMA,
Triethyleneglycoldimethacrylates,
Glycerophosphatedimethacrylates,
Bariumaluminopolosilicate glass,
Others.
Unidirectional pre-tensed quartz
fibers: 60% vol. Epoxy resin: 40%
vol. Fiber density: 32/mm2.
Translucent, double flared. Apical
diameter: 1.2 mm. Apical taper: 0.02.
Coronal diameter: 2.2 mm. Coronal
taper: 0.10.
Unidirectional pre-tensed quartz
fibers coated with silicate/silane and a
protective layer made of MMA: 60%
vol. Epoxy resin: 40% vol. Fiber
density: 32/mm2.
Translucent, double flared. Apical
diameter: 1.2 mm. Apical taper: 0.02.
Coronal diameter: 2.2 mm. Coronal
taper: 0.10.
DT Light Post
(Vereinigte Dentalwerke)
Batch n°: 120US0401A
DT Light SL Post
(Vereinigte Dentalwerke)
Batch n°: 05/65
Mix capsule for 2-4 s and
the insert it into the
Aplicap Applier. Attach
the elongation tip to the
applicator. Apply cement
in the root canal from
bottom to top. Self-cure for
5 min and light-cure for
40s.
Automix cement. Apply,
self-cure for 5 min and
light-cure for 40 s.
-
-
Results
Push-out bond strength test
Mean (SD) push-out bond strengths are displayed in Table 2. Bond
strengths of RelyX Unicem were statistically higher than those recorded
for Max-Cem (p<0.05). Post treatment did not influence bond strength of
RelyX Unicem (p>0.05). Max-Cem attained superior bond strength when
187
bonded to silanated posts. No significant differences were found among
the other tested treatments.
Failure mode distribution of the experimental groups are presented in
Table 3. A predominance of adhesive failures at the cement/dentin
interfaces were recorded for RelyX Unicem, independently from the post
conditioning treatment. Mixed (2-5%) and adhesive failures (38-44%)
between Max-Cem and the hydrogen peroxide etched- and sandblastedposts was recorded, while cement/dentin debondings were prevalent when
Max-Cem luted the non treated, silanated and/or industrially coated posts.
Cohesive failures (from 2% up to 34%) within the cement were also
registered for Max-Cem in all the experimental groups. No cohesive
failures of the posts were observed.
Table 2: Mean (SD) bond strengths (MPa) recorded for the self-adhesive cements used for luting
conditioned fiber posts. Different letters in each column and asterics in each row indicate
statistically significant differences among the experimental groups (p<0.05).
Experimental groups
Unicem
Maxcem
Silane (DT Light Post)
7.24 (2.45) A
4.79 (2.06) B*
7.25 (2.42) A
1.63 (1.23) A*
7.02 (3.14) A
1.15 (1.09) A*
6.25 (2.46) A
1.83 (1.94) A*
9.3(2.6)
3.86(2.94) A*
Hydrogen peroxide (10%)
Sandblasting (Rocatec Pre)
Silicate/silane coating (DT
Light SL post)
DT Light Post
188
Table 3. Percentage of failure recorded in each experimental group. AD: adhesive failures occurred
between the cement and the dentin; AP: Adhesive failures between cement and post; C: cohesive
failures observed within the cement; M: Mixed failures, a combination of AD and AP.
Experimental groups
Unicem
Maxcem
Failure Mode
AD
AP
C
M
AD
AP
C
M
Silane (DT Light Post)
100%
-
-
-
83%
-
17%
-
100%
-
-
-
58% 38%
2%
2%
100%
-
-
-
48% 44%
3%
5%
100%
-
-
-
66%
-
34%
-
19% 6% 6% 85%
-
34%
-
Hydrogen peroxide (10%)
Sandblasting (Rocatec Pre)
Silicate/silane coating (DT
Light SL post)
DT Light Post
69%
Scanning electron microscopy (SEM)
Representative SEM images of debonded slices are presented in
Figs. 1 and 2. RelyX Unicem resulted in a continuous bonded interface
when luting silanated posts (Fig.1A). Micro-spaces were created on the
post surface after 10% hydrogen peroxide etching and mechanical
blasting. The cement was able to flow into the micro-porosities forming
tight bonded interfaces (Fig. 1B and C). The fibers of the industrially
silicate/silane coated post surface appeared wrapped in the coating blend
(Fig. 1 D). The cement structure was compact and nor voids neither
bubbles were highlighted (Fig. 1E).
Max-Cem was able to properly bond to the post after silane
application; nevertheless, voids were observed within the cement bulk and
more irregular interfaces were assessed at the dentin side (Fig. 2A). The
189
cement appeared unable to penetrate the microretentive spaces formed on
the post surface after 10% hydrogen peroxide etching and sandblasting
(Figs. 2B and 2C). Tight adhesive interfaces were formed when Max-Cem
was luted to the industrially coated DT Light SL Post (Fig. 2D), although
porosities were observed within the cement thickness (Fig. 2E).
A
C
E
B
D
Fig. 1: Representative SEM images of
fiber posts cemented with RelyX Unicem
after different chemo/mechanical surface
pre-treatments (1.000x, 10 bar). A)
Silanized post (DT Light Post); B) After
etching with 10% hydrogen peroxide; C)
After sandblasting (Rocatec Pre); D)
Silicate/silane coating (DT Light SL Post,
VDW); E) No treatment (DT Light Post).
Adhesive failures at the cement/dentin
interface were predominant in all the
experimental
groups.
The
cement
appeared well adherent to the post
substrate, independently of the post
surface pre-treatment performed. In the
DT Light SL Post image (D) the glass
fibers were completely wrapped into the
resin.
190
A
B
C
D
Fig. 2: SEM photographs of fiber posts cemented
with Maxcem after different post surface pretreatments (1.000x, 10 bar). A) Silanated (DT light
Post); B) After etching with 10% hydrogen peroxide;
C) After sandblasting (Rocatec Pre); D)
Silicate/silane coating (DT Light SL Post); E) No
treatment (DT Light Post). Maxcem was adherent to
silanated post, even though the cement appeared
viscous and inhomogeneities were observed at the
interfaces. No tight bonded interfaces at the posts side
were evident in the others groups. Although rough
post surfaces were created after the chemomechanical treatment, the material is not able to
penetrate the spaces created.
E
Discussion
The null hypothesis has to be rejected as post surface treatments
influenced the bond strengths of the tested self-adhesive cements.
Differences exist between the attained bond strengths of RelyX Unicem
and Max-Cem.
191
A reliable bonding between post/cement and cement/dentin is
guaranteed when strong joints are simultaneously created at the two
adhesive interfaces. Although bonding to radicular dentin may be
considered as the weakest point of a fiber post-restored tooth, debondings
at the fiber post/resin cement interfaces may also compromise the clinical
outcome of the restoration (Cagidiaco et al, 2007) (Ferrari et al, 2007b)
(Hagge et al, 2002) (Ferrari et al, 2000). Bonding of resin cements to fiber
posts is based on a chemical interaction. However, the combination of
chemical interaction and mechanical retentions may be of help for
increasing their retentive strength (Monticelli et al, 2008). In general, this
is possible by treating the fiber post surface with chemo-mechanical
procedures which are intended to eliminate/dissolve the epoxy matrix of
the fiber posts, considered unsuitable to establish chemical bonds with
methacrylate based materials, and to expose the underneath fibers that can
be then activated and readily react with the resinous cement (Monticelli et
al, 2006) (Monticelli et al, 2008b) (Vano et al, 2006).
The application of a silane coupling agent on fiber post surface
resulted in different bonding behaviours of the tested self-adhesive
cements: no increase in the bond strength values were assessed for RelyX
Unicem, whereas Max-Cem attained superior retentive strength when
compared to the other experimental groups, notwithstanding the push-out
bond strength values of Max-Cem were inferior to those recorded with
RelyX Unicem (Table 2). Previous findings are controversial regarding the
real benefits of fiber post silanization for improving the adhesion to
composite materials.5,7,18 The alkoxy groups of organosilanes establish
chemical bridges with OH-covered substrates, such as glass fibers, and
increase the surface wettability. The application of a silane coupling agent
192
before luting with the self-adhesive cement was previously questioned
(Hayashi et al, 2008) (Bitter et al, 2007). In the present study, the
cement/post interfaces were homogeneous for the tested cements (Figs. 1A
and 2A) and no adhesive failures at the fiber post side were found (Table
3). However, the failure analysis revealed a predominance of adhesive
debondings at the cement/dentin side (Table 3), still highlighting concerns
regarding the effective sealing ability of these simplified resin cements
(Watzke et al, 2008).
Hydrogen peroxide etching was proposed as an alternative fiber post
surface treatment (Monticelli et al, 2006) (Vano et al, 2006). The chemical
etching procedure increased the fiber post surface roughness, the epoxyresin matrix was partially dissolved and the fibers were exposed and
undamaged. The microretentive spaces created on fiber post surface
represented sites where the material could flow and establish stronger
mechanical retentions (Monticelli et al, 2006) (Monticelli et al, 2008b).
However, according to the obtained results, etching the fiber post surface
with 10% hydrogen peroxide for 20 min did not improve the bond strength
values of the tested cements (Table 2). The SEM images revealed an
intimate contact between RelyX Unicem and the etched fiber post, as the
material homogeneously flowed into the retentive site bonds formed (Fig.
1B). On the contrary, discontinuous interfaces were evidenced between
Max-Cem and the hydrogen peroxide treated fiber post (Fig. 2B). The
inherent viscosity of the material may hamper its penetration into the
created micro-porosities (Monticelli et al, 2005). The presence of gaps at
the bonded interfaces would negatively affect the ultimate adhesion
mechanism, representing sites from which stresses may be expedited
(Mazzitelli et al, 2007). The presence of voids and bubbles into the cement
193
bulk may also have accounted for the high number of mixed and cohesive
failure registered for Max-Cem (Table 3). This phenomenon can be
attributed to the different dispensing modalities. RelyX Unicem was
directly injected into the root canal by means of a specific elongating tip,
whereas Max-Cem was manually mixed and then inserted into the canal
with a lentulo spiral and applied directly on the post. The use of a flexible
root-canal shaped elongating tip is advisable in order to reach the deeper
apical third of the root canal and avoid undesirable air-bubble entrapments
and imperfections within the cement bulk (Watzke et al, 2008) (Simonetti
etal, 2008).
Sandblasting is a mechanical procedure intended to provide a plastic
deformation and to improve the surface roughness of a fiber post, resulting
in an increased surface areas for bonding (Kern et al, 1994). This
procedure determined higher bond strengths of fiber posts into root canals
and no damages of the glass fibers were manifested (Sahafi et al, 2003)
(Mazzitelli et al, 2008). The time and the distance of application and the
size of aluminium-oxide particles were all considered factors determining
the effect of the blasting procedure. In the present study, sandblasting of
fiber post was performed using 110 µm aluminium-oxide particles blasted
for 5 s on the post surface at a distance of 1 cm. This resulted in mild
conditioning effect which was considered advantageous for treating fiber
posts when compared to other aggressive procedures, such as hydrofluoric
acid (Vano et al, 2006) (Mazzitelli et al, 2008). Based on the SEM
images, the mechanical blasting created roughened fiber post surface with
the formation of micro-spaces. Although RelyX Unicem was able to flow
along with these retentive spaces (Fig. 1C), it did not represent an
additional advantage that could improve the bond strengths (Table 2).
194
Max-Cem produced irregular cement/fiber post interfaces, being difficult
to diffuse into the created grooves (Fig. 2C) and no differences in its
retentive strength were found when compared to the hydrogen peroxide
etched, silicate/silane coated and non treated groups (Table 2).
The industrially treated fiber posts have been recently introduced in
the market in the attempt of simplifying the clinical procedures while
ensuring reliable bonding. The post inner structure is wrapped in the precoating blend, and nor the epoxy resin nor the fibers are exposed.
Accordingly, the bonding mechanism is based on the chemical interaction
between the silicate/silane coating and the luting cement with no direct
involvement of the epoxy-rein matrix (Mazzitelli et al, 2008). So, more
stable bonds are supposed to be formed. However, no differences in bond
strengths were observed for RelyX Unicem in comparisons with non
treated posts. Max-Cem recorded inferior bond strengths when luted to DT
Light SL Post and compared to the silanated post (Table 2). Based on the
findings of a previous report, the industrially coated fiber post is
superficially smooth leaving no chance to develop micromechanical
interlocking (Mazzitelli et al, 2008). Additionally, due to the high acidity
of the cement, the formation of a layer of acidic monomers on the post
surface would hamper the chemical reaction with the post and this, plus
the lack of mechanical retentions, may have accounted for the high
percentage of debondings at the cement/fiber post side (Table 3) (Wrbas et
al, 2007).4
The concept of an ―ideal monoblock‖ inside the root canal should
further be investigated. According to the circumferential interfaces created
for the cementation of fiber posts into radicular dentin, three type of
monoclock units can be individuated (Tay et al, 2007). Self-adhesive
195
cements seemed to represent the secondary monoblock, as they can form
two bonding interfaces: the cement/dentin and the cement/fiber posts. In
order to be successfully and mechanically validated as effective bonding
agents, they should possess two main prerequisite: 1) the cement has to
strongly bond to the radicular dentin and to the fiber post; 2) the cement
has to show a moduli of elasticity similar to the bonding substrates. The
fiber posts, the cement and the dental substrate have to show similar
moduli of elasticity in order to better distribute the stresses along the root.
The involvement of a third interface would make the idea of monoblock
more complex. When using the DT Light SL Post, another interface is
introduced between the bonding substrates: the external silicate/silane
coating transform the bond into a tertiary monoblock unit (Tay et al,
2007). In general, although the effectiveness of self-adhesive cements has
previously been emphasized, further studies are highly warranted to
improve the bonding mechanism of these simplified cements used for the
cementation of fiber posts into root canal. In addition, more information
regarding their mechanical properties (i.e. moduli of elasticity,
polimerization shrinkage) is needed.
Within the limits of the present investigation, it can be concluded
that the effectiveness of post surface treatments on the bond strength of
self-adhesive cements is material-related. No increasing in bond strength
would be expected for RelyX Unicem, whereas it seemed necessary to
pre-treat the fiber post surface with silane solutions when using Max-Cem
for luting fiber posts.
196
References
Cagidiaco MC, Radovic I, Simonetti M, Tay FR, Ferrari M. Clinical
performance of fiber post restorantions in endodontically treated teeth: 2year results. Int J Prosthodont 2007; 20: 293-298.
Ferrari M, Cagidiaco MC, Grandini S, De Sanctis M, Goracci C.
Post placements affects survavil of endodontically treated premolars. J
Dent Res 2007; 86: 729-734.
Schwartz RS, Robbins JW. Post placement and restoration of
endodontically treated teeth: a literature review. J Endod 2004; 30: 289301.
Monticelli F, Toledano M, Osorio R. The application of superficial
treatments to improve bond strength to fiber posts. In: Ferrari M, Breschi
L, Grandini S. Fiber posts and endodontically treated teeth: A
compendium of scientific and clinical perspectives. Ed. Modern Dentistry
Media, 2008; Chap. 7: 85-93.
Perdigao J, Gomes G, Lu IK. The effect of silane on bond strengths
of fiber posts. Dent Mater 2006; 22: 752-8.
Monticelli F, Toledano M, Tay FR, Cury AH, Goracci C, Ferrari M.
Post surface conditioning improves interfacial adhesion in post/core
restorations. Dent Mater 2006; 22: 602-9.
Aksornmuang J, Foxton RM, Nakajima M, Tagami J. Microtensile
bond strength of a dual cure resin core material to glass and quartz fiber
posts. J Dent 2004; 32: 433-450.
Tay FR, Pashley DH. Monoblocks in root canals: a hypothetical or a
tangible goal. J Endod 2007; 33: 391-398.
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Ferrari M, Cagidiaco MC, Goracci C, Vichi A, Mason PN, Radovic
I, Tay F. Long-term retrospective study of the clinical performance of
fiber posts. Am J Dent 2007; 20: 287-91.
Baldissara P, Zicari F, Valandro LF, Scotti R. Effect of root canal
treatments on quartz fiber posts bonding to root dentin. J Endod 2006; 32:
985-8.
Monticelli F, Osorio R, Sadek FT, Radovic I, Toledano M, Ferrari
M. Surface treatments for improving bond strength to pre-fabricated fiber
posts: a literature review. Oper Dent 2008; 33: 346-55.
Vano M, Goracci C, Monticelli F, Tognini F, Gabriele M, Tay FR,
Ferrari M. The adhesion between fiber posts and composite resin cores:
the evaluation of microtensile bond strength following various surface
chemical treatments to posts. Int Endod J 2006; 39: 31-9.
Mazzitelli C, Ferrari M, Toledano M, Osorio E, Monticelli F, Osorio
R. Surface roughness analysis of fiber post conditioning processes. J Dent
Res 2008; 87: 186-90.
Toman M, Toksavul S, Sankanat M, Firidinoglu K, Akin A. The
evaluation of displacement resistance of glass FRC posts to root dentin
using a thin slice push-out test. Int Endod J 2009; 42: 802-810.
Bateman GJ, Lloyd CH, Chadwick RG, Saunders WP. Retention of
quartz-fibre endodontic posts with a self-adhesive dual-cure resin cement.
Eur J Prosthodont Restor Dent 2005; 13: 33-37.
Hayashi M, Okamura K, Wu H, Takahashi Y, Koytchev EV,
Imazato S, Ebisu S. The root canal bonding of chemical-cured total-etch
resin cements. J Endod 2008; 34: 583-586.
Wrbas KT, Altenburger MJ, Schirrmeister JF, Bitter K, Ktelbassa
AM. Effect of adhesive resin cements and post surface silanization on the
198
bond strengths of adhesively inserted fiber posts. J Endod 2007; 33: 840843.
Bitter K, Noetzel J, Neumann K, Kielbassa AM. Effect of
silanization on bond strengths of fiber posts to various resin cements.
Quintessence Int 2007; 38: 121-128.
Hagge MS, Wong RDM, Lindhemut JS. Retention strength of five
luting agents on prefabricated dowels after root canal obturation with a
zinc oxide/eugenol sealer. J Prosthodont 2002; 11: 168-175.
Ferrari M, Vichi A, Mannocci F, Mason PN. Retrospective study of
clinical behavior of several types of fiber posts. Am J Dent 2000; 13: 14B19B.
Sarr M, Mine A, De Munck J, Cardoso MV, Kane AW, Vreven J,
Van Meerbeek B, Kirsten L, Van Landuyt KL. Immediate bonding
effectiveness of contemporary composite cements to dentin. Clin Oral
Investig 2009; doi: 10.1007/s00784-009-0327-8.
Mazzitelli C, Magni E, Radovic I, Papacchini F, Goracci C, Ferrari
M. The adhesion between FRC posts and resin core materials following
different treatments of the post surface. International Dentistry SA 2007;
9: 30-40.
Watzke R, Blunck U, Frankenberger R, Naumann M. Interface
homogeneity of adhesively luted glass fiber posts. Dent Mater 2008; 24:
1512-7.
Simonetti M, Coniglio I, Magni E, Cagidiaco MC, Ferrari M.
Sealing ability and microscopic aspects of a self-adhesive resin cement
used for fiber post luting into root canals. International Dentistry SA 2008;
8: 24-30.
199
Chapter 7
7.1 Summary, Conclusions and Future Directions
The selected luting material and the cementation procedures may
influence the retention and durability of prosthetic restorations. Luting
materials and techniques have been widely investigated both in the clinical
practice and research attempting to simplify them while ensuring a certain
longevity of the prosthetic restoration. The issues related to this topic
include the evaluation of the bond strength, the effectiveness of the
cements as sealing agents, the interaction with the dental substrates and
the restorations, the dispensing modality and mechanical properties. A
simplification of the
luting procedures was made possible with the
introduction of self-adhesive cements. Self-adhesive resin cements have
been defined as ―universal‖ as they can lute different types of indirect
restorations, such as fiber posts, zirconia/ceramic crown and/or bridges,
composite inlays/onlays, and screws. According to manufacturers claims,
only veneer cementation should be avoided.
In the initial part of this project (Chapter 1), an introduction of the
main topic of the study has been presented. After a short description of the
luting procedures nowadays available for luting indirect restorations, the
introduction went deeply to analyze the cement systems characteristics,
focusing on those of self-adhesive resin cements. In particular, the data
available into the literature regarding the bonding effectiveness of selfadhesive resin cements used to lute composite onlays, fiber posts or
ceramic crowns were analyzed. The scope of the auto-adhesive technology
was to simplify luting procedures and overcome the difficulties related to
200
the multi-step cement systems, such as the high-influence of the operator
variability and the chemical incompatibility that can occurs when using
dual-curing luting agents with their simplified adhesive systems. However,
differences in the chemical composition, dispensing modality, pH and
mechanical properties influence the bonding mechanism of the simplified
cements. In particular, the interaction between these cements and the
dentin substrate is still a matter of study, and research is now focused to
improve this site bond. The ability of self-adhesive cements to lute fiber
posts was also considered with and without thermal ageing test, and the
possibility to combine pre-treated posts with the simplified cements was
analyzed.
In the second part of this thesis (Chapter 2), the study was centrated
to deeply analyze the interaction between simplified self-adhesive cements
and the dentin substrate. An observational study based on light and
scanning electron microscopy allowed to compared the interfacial
characteristics (in terms of dentin demineralization/resin penetration) of
self-adhesive cements and resin cements that use a total-etch and a selfetch adhesive. Differences between the material were encountered,
showing that a total-etch cement system was able to deeply demineralize
the dentin substrate. Self-adhesive cements showed only limited capacity
to interact with dentin.
In Chapter 3, bond strength and scanning electron microscopy
evaluations of different self-adhesive cements to perfused dentin was
presented. Again, a total-etch resin cements was used for comparisons.
The hydration state of dentin differently influence the tested cements.
While having a detrimental effects on the multi-step resin cement, the
presence of pulpal pressure may be beneficial during the cementation of
201
selected self-adhesive cements. A more specific classification of the
simplified resin cements was made, as some of them showed some
silicate-like cement characteristics. In presence of vital dentin, certain
cements could be advisable for the cementation procedures, while
attention should be paid when using multi-step resin cements, since water
can permeate through dentinal tubules, reaching the adhesive interfaces
and hamper a proper setting reaction of the cement itself. In this terms, the
simulation of an hydrostatic intra-pulpal pressure should be taken into
consideration when performing luting procedures in vitro.
Although self-adhesive cements do not need pre-treatments of
dentin, in Chapter 4 the attention has been focused to the possibility of
conditioning the dental substrate with mild acidic solutions (0.1 M EDTA
and 10% polyacrylic acid) before cement application in order to improve
the cement/dentin interactions. According to the microtensile bond
strength values recorded, differences in the bonding performance of selfadhesive cements were found. An improved adhesion was recorded when
a self-adhesive cement, that showed glass-ionomer-like characteristics,
was luted on 10% polyacrylic acid etched dentin. The Masson’s staining
technique for optical microscopy allowed to individuate the interfacial
characteristics of the three self-adhesive cements tested under the
experimental conditions. However, scarce cement/dentin interaction was
observed, and, in particular, exposed collagen fibers were found at the
bottom of the adhesive interfaces renewing concerns regarding the
effective sealing ability of the simplified resin cements.
In Chapter 5, two studies based on the evaluation of the bonding
performance of self-adhesive cements to fiber posts were performed. In
Paragraph 5.1 the push-out bond strengths of three self-adhesive cements
202
used to lute epoxy-resin based fiber posts into radicular dentin were
evaluated. The results of the study indicate that differences can be found
between the bonding mechanism of the self-adhesive resin cements mainly
due to their different chemical compositions, that make necessary a deep
classification of this new class of resin cements. The cement application
mode into the post space was also considered an important factor
influencing the results obtained. The quality of the adhesive interface can
be affected by the operative procedure, so the use of an elongating tip is
advisable for placing the cement into the post space. The various
indications coming from the results of the study described before found a
confirmation in Paragraph 5.2, in which a durability test was performed.
Three differently marketed self-adhesive resin cements were used to lute
fiber posts and their bond strengths were examined prior and after being
submitted to 5.000 cycles of thermal ageing. This study revealed that the
thermal stresses did not affect the push-out bond strength values of RelyX
Unicem and Breeze, whereas increased those of G-Cem. A combination of
chemical interactions and micro-mechanical retentions seemed to
characterize the bonding mechanism of self-adhesive cements to fiber
posts. Although the incidence of adhesive failure at the cement/dentin side
was relevant, decementations at the cement/fiber post interfaces occurred
in all the experimental groups.
More precisely, fiber reinforced material technology gave suggestion
to test different fiber post superficial treatments with the aim of obtaining
an effective adhesion. A series of preliminary observations were
conducted in Chapter 6. A research was carried out and described in
Paragraph 6.1: confocal microscopy and atomic force microscopy
evaluations were combined to evaluate the effects of different
203
chemo/mechanical fiber post surface treatments on their surface
topographies and average surface roughness. This approach successfully
validated the use of
potassium permanganate, sodium ethoxide and
sandblasting to treat the post surface among the tested conditioning
procedures:
increased
surface
roughness
through
the
partial
removal/dissolution of the expoxy-resin matrix would improve the surface
area available for adhesion by creating micro-retentive spaces.
Conversely, hydrofluoric acid was considered an aggressive conditioning
method, as it caused excessive damages of the quartz fibers. In Paragraph
6.2, the influence of fiber post superficial treatments on the retentive
strength of self-adhesive resin cements used to lute epoxy-resin based
fiber posts into radicular dentin was considered. Non destructive
chemo/mechanical conditioning approaches were adopted for treating fiber
posts and two self-adhesive cements were used. Post surface conditionings
did not improved the retention of RelyX Unicem to fiber posts, whereas
Max-Cem additionally benefit of the application of a silane coupling agent
to optimize the bond strength. However, the viscosity of the materials
seemed to hamper the complete penetration of the cements into the microspaces created by the conditioning approaches. Differences were also
found between the luting agents. An inferior percentage of defects was
detected when an elongating tip was used to place the cement into the
dowel space. The use of application aids is highly advisable to limit the
occurrence of defects and air-entrapment into the cement bulk.
204
Conclusions
The following conclusions can be drawn from the laboratory
researches based on the evaluation of the bonding potential of different
self-adhesive resin cements employed for the cementation of coronal
composite restorations and/or fiber posts:
1) A limited interaction with dentin characterize the bonding behavior
of self-adhesive resin cements when compared to a total-etch or a
self-etch adhesive systems. In particular, the chemical composition
of each product influences their bonding mechanism.
2) The hydration state of dentin should be taken into consideration
when restoring a vital tooth. The continuous water fluid flow
through dentinal tubules can influence the bonding effectiveness of
luting cements; in particular it can be detrimental for cements that
utilize multi-step adhesive systems. Conversely, self-adhesive resin
cements, take benefits from the water transudation as a setting
reaction similar to that of silicate cements can be postulated.
3) Considerations should be made when pre-treating dentin with mild
acidic solutions before luting indirect restorations with selfadhesive cements. Dentin etching with 10% polyacrylic acid could
be proposed before using selected self-adhesive cements.
4) Differences exist between the bonding potential of different selfadhesive resin cements used to lute fiber posts into radicular
dentin. The dispensing modality affect their bonding mechanism
and the use of an elongating tip become necessary to avoid any
defect within the cement bulk.
5) Thermal ageing does not affect the bonding potential of the tested
self-adhesive cements. An improved setting reaction is speculated
205
in presence of high temperature. A combination of chemical
reactions and micro-mechanical retentions characterize the selfadhesive cements bonding to fiber posts.
6) Surface conditioning procedures that selectively react with the
epoxy-resin matrix of the fiber post enhance roughness and
improve the surface area available for adhesion by creating microretentive spaces without affecting the post’s inner structure.
Hydrofluoric acid affects the superficial texture of quartz fibers.
7) Fiber posts surface treatments do not improve the retention of selfadhesive resin cements. The viscosity of the materials hampers
their penetration into the micro-spaces created on the post surface
after the conditioning modalities. The adhesion to radicular dentin
remains an ―hot topic‖ which need to be optimized.
Future directions
Dental research targeted at the development of ideal materials has
been ongoing for many years. Since its introduction in the late 50s,
adhesion has undergone considerable maturation, increasing the role
exerted in daily practice and dental investigation. The desire to obtain a
long lasting prosthetic restoration with simple and less time consuming
cementation procedures is a driving force behind the continuous quest of
clinicians and dental manufacturers and leads researchers to continuously
develop their thoughts. The self-adhesive technology is undoubtedly
innovative and open the door to a simplified cementation procedure.
However, many limitations may moderate their clinical use. Innovations
should be performed on the adhesion mechanism to dentin (coronal and
radicular).
206
Some characteristics of self-adhesive cements, in terms of viscosity
or contraction stress, should be improved and tested. Techniques intended
to reduced the high viscosity of the materials are necessary in order to
enhance a deeper penetration of the resin into the demineralized dental
tissue or into the conditioned restoration. Future studies should also
evaluate the shrinkage percentage of the simplified resin cements in
presence of an high C-factor (i.e. into root canal).
There are no doubts that clinical studies are highly warranted in
order to validate the results presented in the present doctoral thesis and to
make these cements totally clinically recommendable.
207
7.2 Riassunto, Conclusioni e direzioni future
L’esito di un restauro protesico è direttamente relazionato al tipo di
materiale e alla tecnica di cementazione utilizzati. La ricerca dei materiali
è costantemente concentrata a individuare e migliorare i materiali e le
tecniche da cementazione in maniera da favorire una certa longevità del
restauro. In generale, i temi relazionati allo studio dei materiali da
cementazione si riferiscono principalmente alla valutazione della forza di
adesione, alla capacità sigillante dei suddetti prodotti, l’interazione tra il
cemento e i substrati dentali e i differenti materiali da restauri, le modalità
di applicazione e le proprietà meccaniche. L’introduzione dei cementi
resinosi auto-adesivi ha permesso di semplificare le tecniche di
cementazione. Questi cementi sono stati definiti ―universali‖, in quanto
capaci di legarsi a diversi tipi di restauri, come ai perni in fibra, corone o
ponti in zirconia/ceramica, inlays/onlays di composito e screws. Secondo
quanto consigliato dai produttori, è sconsigliata la cementazione di
faccette con i materiali semplificati. Nella parte iniziale di questo progetto
(Capitolo 1), è stato presentato l’obiettivo prefissato nello studio. Dopo
una breve descrizione dei materiali e delle tecniche da cementazione
attualmente disponibili, l’introduzione si è concentrata a descrivere le
caratteristiche dei vari cementi, focalizzando l’attenzione sui cementi
resinosi auto-adesivi. In particolare, sono stati analizzati i dati presenti
nella letteratura dentale riguardo l’utilizzo dei cementi auto-adesivi per la
cementazione di onlays in composito o perni in fibra. Lo scopo principale
dei cementi auto-adesivi è stato quello di semplificare le tecniche di
cementazione limitando le difficoltà riscontrate con l’utilizzo di cementi
che utilizzano sistemi adesivi a tre o due passaggi, come per esempio la
208
grande influenza dell’operatore, e l’incompatibilità chimica che si può
verificare tra i cementi duali e i sistemi adesivi semplificati. Il
meccanismo di adesione dei cementi one-step può essere influenzato dalla
loro composizione chimica, pH, modalità di applicazione e proprietà
meccaniche. In particolare, il conoscimento del tipo di interazione tra i
cementi resinosi semplificati e la dentina è continuamente oggetto di
studio, e attualmente la ricerca si propone di migliorare il tipo di adesione.
L’abilità dei cementi auto-adesivi utilizzati per la cementazione dei perni
in fibra è stata inoltre presa in considerazione, in presenza o meno di stress
termici, così come è stata anche analizzata la possibilità di combinare la
semplicità di utilizzo dei suddetti cementi con perni in fibra pre-trattati in
superficie con metodiche chimico/meccaniche.
Nella seconda parte di questa tesi (Capitolo 2), l’attenzione è stata
focalizzata nell’analizzare più approfonditamente l’interazione tra i
cementi auto-adesivi e il substrato dentinario. Le osservazioni sono state
condotte utilizzando la microscopia elettronica a scansione (SEM) e la
tecnica tricromia di Masson per la microscopia ottica, che, unitamente,
hanno permesso di comparare le caratteristiche dell’interfaccia (in termini
di demineralizzazione del substrato dentale/penetrazione del materiale
resinoso) tra i cementi auto-adesivi e cementi che utilizzano sistemi
adesivi a tre o due passaggi. I risultati dello studio hanno rivelato che
esistono differenze tra i materiali testati, mostrando una maggiore abilità
per i cementi resinosi che utilizzano sistemi adesivi a demineralizzare la
dentina. Al contrario, i cementi semplificati hanno dimostrato una minore
capacità di interazione con il substrato dentale.
Nel Capitolo 3, è stato presentato uno studio basato su misurazioni
della forza di adesione e valutazioni con miscoscopia elettronica a
209
scansione dei cementi adesivi utilizzati su dentina in presenza di pressione
pulpare. Nuovamente, un cemento total-etch è stato utilizzato per la
comparazione. I dati ottenuti hanno dimostrato che in presenza di
pressione pulpare, i cementi testati si comportano diversamente. Da un
lato, i cementi resinosi total-etch non traggono beneficio dalla presenza di
perfusione dentina ria, mentre i cementi auto-adesivi si comportano in
maniera differente. E’ stato quindi possibile fare una classificazione più
specifica dei cementi semplificati, dal momento che alcuni dei materiali
testati hanno dimostrato possedere caratteristiche simili a quelle dei
cementi silicati. Per questo che, quando si restaura un dente vitale, alcuni
cementi
auto-adesivi
possono
essere
consigliabili
nelle
fasi
di
cementazione, mentre altri materiali dovrebbero essere utilizzati con
cautela, dal momento che l’acqua procedente attraverso i tubuli dentinari
può raggiungere l’interfaccia adesiva, mescolarsi al materiale non ancora
indurito e interferire con l’ultima fase della polimerizzazione. Inoltre,
avendo osservato diversi comportamenti tra i materiali, la simulazione di
pressione idrostatica dovrebbe essere preso in considerazione quando si
adoperano procedure di cementazione in vitro.
Nonostante i cementi auto-adesivi non richiedono alcun previo
trattamento della dentina e dei restauri, l’obiettivo dello studio del
Capitolo 4 è stato prendere in considerazione la possibilità di trattare la
dentina con soluzione acide deboli (0.1 EDTA e acido poliacrilico al 10%)
prima di applicare i cementi auto-adesivi con l’intenzione di migliorare
l’interazione tra i due substrati adesivi. I dati della forza di adesione
microtensile hanno evidenziato differenze nella performance adesiva dei
materiali testati. L’interazione adesiva è stata migliorata solo per un
cemento che dimostra una tecnologia simile a cementi vetro-ionomerici e
210
utilizzato su dentina mordenzata con il 10% di acido poliacrilico. La
colorazione tricromia di Masson ha permesso, inoltre, di individuare le
caratteristiche dell’interfaccia tra i tre materiali utilizzati e la dentina. In
generale, una scarsa interazione cemento/dentina è stata osservata per tutti
e tre i cementi testati, evidenziando, in particolare, la presenza di fibre
collagene non encapsulate alla base dell’interfaccia adesivi, rinnovando
nuovamente dei dubbi riguardo alla effettiva capacità sigillante fornita dai
cementi resinosi semplificati.
Nel Capitolo 5, sono stati presentati due studi basati sulla
valutazione della capacità adesiva dei cementi auto-adesivi per la
cementazione di perni in fibra. Nel Paragrafo 5.1, è stata valutata la forza
di adesione push-out di tre cementi auto-adesivi utilizzati per la
cementazione di perni in fibra con una matrice a base di resina epossidica
all’interno del canale radicolare. Le principali differenze annoverate tra le
diverse capacità adesive dei materiali testati sembra più essere legata alle
differenti composizioni chimiche. Di contro, una classificazione più
dettagliata dei nuovi cementi auto-adesivi dovrebbe essere presa in
considerazione. Inoltre, il modo di applicazione del cemento all’interno
dello spazio endodontico può influenzare i risultati, per questo che
l’utilizzo di un puntale elastico dovrebbe essere consigliato per permettere
l’inserimento del cemento. Le indicazioni riscontrate nel precedente
studio, hanno trovato conferma nel Paragrafo 5.2, dove è stato eseguito
un test di durabilità. Tre cementi auto-adesivi sono stati impiegati per
cementare i perni in fibra e la loro forza di adesione è stata determinata
prima e dopo essere stati sottoposti a 5.000 cicli di stress termici. I risultati
ottenuti hanno dimostrato che il termociclaggio non ha influenza sulle
forza di adesione di RelyX Unicem e Breeze, mentre hanno migliorato
211
quella di G-Cem. Un insieme di interazione chimica e ritenzione
meccanica sembra caratterizzare il meccanismo di adesione dei cementi
semplificati ai perni in fibra nel canale radicolare. Nonostante il numero di
fallimenti adesivi tra cemento e dentina, è stato anche registrato un alto
numero di decemntazioni cemento/perno in fibra in tutti i gruppi
sperimentali.
Più precisamente, la tecnologia dei materiali rinforzati con fibra ha
suggerito l’idea di testare dei pre-trattamenti di superficie dei perni in fibra
con l’obiettivo di migliorare l’adesione ai materiali da cementazione. Una
serie di osservazioni preliminari sono state svolte nel Capitolo 6. Uno
studio è stato condotto nel Paragrafo 6.1: valutazioni con microscopia
confocale e microscopia a forza atomica sono state svolte per valutare gli
effetti di trattamenti di superficie con metodiche chimico/meccaniche sulla
topografia dei perni in fibra e sulla loro rugosità superficiale. Questo
approccio ha validato l’utilizzo del permanganato di potassio, etossido di
sodio e sabbiatura per trattare la superficie dei perni in fibra: l’aumento
della
rugosità
di
superficie
del
perno,
ottenuta
tramite
una
dissoluzione/rimozione della matrice a base di resina epossidica, può
aumentare l’area disponibile per l’adesione tramite la creazione di spazi
micro-ritentivi. Al contrario, l’acido idrofluoridrico ha dimostrato una
eccessiva aggressività, evidenziando danni alle fibre del perno. Nel
Paragrafo 6.2, è stata presa in considerazione l’influenza che i trattamenti
dei perni in fibra con matrice a base di resina epossidica possano avere
sulla capacità ritentiva dei cementi auto-adesivi. Sono stati, quindi,
utilizzati i trattamenti di superficie non aggressivi precedentemente
elencati e due cementi auto-adesivi. I trattamenti di superficie dei perni in
fibra non hanno influenzato la forza di adesione di RelyX Unicem, mentre
212
Max-Cem ha avuto beneficio dalla previa applicazione di una gente silano
sulla superficie del perno. La viscosità del cemento può, comunque,
ostacolare la completa penetrazione della resina negli spazi ritentiv creati
dopo i trattamenti chimico/meccanici. Differenze sono state inoltre
riscontrate per i due cementi testati, e un minor numero di difetti è stato
visto quando il materiale è stato introdotto nello spazio endodontico
utilizzando il puntale elastico. Per questo che l’utilizzo del suddetto
puntale è clinicamente raccomandabile per evitare l’instaurarsi di difetti
interni e inglobamento di aria nella struttura del cemento.
Conclusioni
Le seguenti conclusioni si possono dedurre dagli studi in vitro
condotti sulla valutazione della capacità adesiva dei cementi resinosi
semplificati utilizzati per la cementazione di overaly in composito su
dentina coronale e/o di perni in fibra:
1) L’interazione cemento auto-adesivo/dentina è limitata quando
comparata a un cemento total-etch. In particolare, le diverse
composizioni chimiche possono influenzare il loro meccanismo di
adesione;
2) Lo stato idratato della dentina deve essere preso in considerazione
quando si tratta un dente vitale. Il continuo flusso di acqua
attraverso i tubuli dentinari influenza il comportamento adesivo dei
cementi; in particolare, può avere effetti detrimenti sulla forza di
adesione dei cementi che utilizzano sistemi adesivi a tre pasaggi,
mentre alcuni cementi auto-adesivi traggono beneficio dalla
213
presenza di acqua, postulando una reazione simile a quella dei
cementi silicati;
3) Alcune considerazioni devono essere fatte quando si desidera pretrattare
la
dentina
con
soluzioni
acide
deboli
prima
dell’applicazione dei cementi auto-adesivi. La mordenzatura della
dentina con una soluzione di acido poliacrilico al 10% può essere
raccomandabile solo per quei cementi che si basano su una
tecnologia simile ai cemento vetro-ionomerici;
4) Differenze nelle forze di adesione esistono tra i vari materiali autoadesivi utilizzati per la cementazione dei perni in fibra. La
modalità di applicazione del cemento nello spazio endodontico
influenza il loro meccanismo di adesione, e l’utilizzo di un puntale
elastico è necessario per limitare i difetti e gli inglobamenti di aria
nella struttura del cemento;
5) Gli stress meccanici non influenzano la forza di adesione dei
cementi auto-adesivi testati. Una combinazione di interazione
chimica e ritenzione micromeccanica caratterizza il meccanismo di
adesione dei cementi semplificati ai perni in fibra nel canale
radicolare;
6) I trattamenti di superficie dei perni in fibra, che reagiscono
selettivamente con la resina epossidica della matrice, aumentano la
loro rugosità e migliorano l’area disponibile per l’adesione tramite
la creazione di spazi micro-ritentivi e senza danneggiare le fibre.
L’utilizzo dell’acido fluoridrico non è consigliabile in quanto
affetta la tessitura superficiale delle fibre del perno;
7) Alcuni trattamenti di superficie dei perni in fibra possono
influenzare la forza di adesione di determinati cementi auto214
adesivi. Comunque, la viscosità del materiale può ostacolare la
completa penetrazione del cemento negli spazi micro-ritentivi
creati dai trattamenti condizionanti del perno in fibra. L’adesione
dei cementi semplificati alla dentina rimane un ―tema caldo‖ che
necessità maggiori chiarimenti.
Direzioni future
La ricerca dentale che si è prefissata di sviluppare materiali con
migliori caratteristiche va avanti da diversi anni. Fin dalla sua prima
introduzione negli anni ’50, il tema dell’adesione ha preso sempre più
piede nella pratica clinica e nella ricerca dentale. Il desiderio da parte dei
dentisti di ottenere restauri protesici duraturi con l’utilizzo di materiali
semplici e che permettano un risparmio di tempo ha incentivato i
ricercatori a sviluppare nuovi pensamenti. La tecnologia auto-adesiva è,
senza dubbio, innovativa e apre le porte a un nuovo metodo, semplice e
veloce, di cementazione. Comunque, alcune limitazione dimostrate nella
letteratura possono limitare il loro utilizzo clinico. Per questo che nuove
innovazioni e miglioramenti dovrebbero essere ottenuti nel loro
meccanismo di adesione alla dentina (sia radicolare che coronale).
Alcune caratteristiche dei cementi auto-adesivi, come la viscosità o
la contrazione da polimerizzazione, dovrebbero essere testate e migliorate.
Tecniche rivolte a diminuire la viscosità dei cementi semplificati sono
necessario, in maniera da favorire una più completa penetrazione della
resina nel tessuto dentale demineralizzato o negli spazi ritentivi dei
restauri pre-trattati. Inoltre, studi futuri dovrebbero focalizzarsi sulla
215
valutazione dello stress da contrazione dei cementi auto-adesivi in
presenza di un alto fattore C (come per esempio, nel canale radicolare).
Sicuramente, studi clinici sono altamente desiderabili per potere
validare i risultati ottenuti nella ricerca e potere così rendere i cementi
auto-adesivi completamente raccomandabili da un punto di vista clinico.
216
7.3 Resumen, Conclusiones y direcciones futuras
El tipo de material y técnica de cementado puede influenciar la
retención y la durabilidad de una restauración indirecta. Estudios clínicos
y de laboratorio se han propuesto de simplificar los materiales y las
técnicas de cementado con el objetivo de preservar la longevidad de la
restauración. Los temas relacionados con este asunto se basan sobre
evaluaciones de la fuerza de adhesión, la habilidad de los materiales de
sellar las interfases adhesivas, la interacción con el sustrato dental y las
superficies de las restauraciones, la modalidad de aplicación y las
propriedades mecanicas. Una simplificación de las técnicas de cementado
se ha hecho posible a través de la introducción en el mercado dental de los
cementos resinosos auto-adhesivos. Estos cementos resinosos han sido
nombrados como ―universales‖ gracias a la capacidad que han
demonstrado de ligarse a varios tipos de restauración, como por ejemplo
los postes de fibra, coronas y/o puentes en zirconia/ceramica, inlay/onlay
de composite, y tornillos. Según las sugerencias de los productores, estos
materiales sólo no son recomendable para el cementado de carillas.
En la parte inicial de esta thesis doctoral (Capítulo 1), se realizó una
introducción al principal argumento en estudio. Tras una breve descripción
de las técnicas actualmente disponibles para el cementado de las
restauraciones indirectas, se comentaron las caracteristicas de los
diferentes cementos utilizados para el cementado, encentrandose en
aquellas de los cementos auto-adhesivos. En particular se analizó el
potencial adhesivo de los cementos resinosos simplificados utilizados para
el cementado de onlays de composite, postes de fibra o coronas de
ceramica. La finalidad de la tecnología auto-adhesiva trata de simplificar
217
las técnicas de cementado y sobrepasar las desventajas de los cementos
resinosos que utilizan los sistemas adhesivos de paso multiple, como por
ejemplo la influencia del operador y la incompatibilidad química que se
verifica entre los cementos duales y los sistemas adhesivos simplificados.
Las diferentes composiciones químicas, la modalidad de dispensación, el
pH, y las propriedades mecanicas, diferencian el mecanismo de adhesión
de los varios cementos simplificados. La interacción entre estos cementos
y el sustrato dental se queda una de las mayores dudas relacionadas con la
técnica simplificada de cementación, y por eso que la investigación se
concentra en mejorar esta interfase adhesiva. Igual se analizó la capacidad
de unión de los cementos auto-adhesivos utilizados para el cementado de
los postes de fibra antes y tras ser submitido a ciclos de termociclado, así
como la posibilidad de combinar los mismos cementos con postes de fibra
pre-condicionados.
En la segunda parte de esta thesis doctoral (Capítulo 2), se evaluó
detallatamente el tipo de relación entre los cementos auto-adhesivos y el
sustrado dental. El estudio se propuso de observar las caracteristicas de las
interfases adhesivas (en particular el grado de desmineralización de la
dentina y la penetración de la resina en la dentina acondicionada)
utilizando diferentes cementos auto-adhesivos y cementos resinosos que
utilizan un sistema adhesivo de grabado total y un otro que utiliza un
sistema adhesivo de grabado y lavado y para la cementación de overlays
de
resina
compuesta.
Las
observaciones
indicaron
diferentes
caracteristicas de las interfases entre los cementos testados, enseňando
como el cemento que se basa en un sistema adhesivo de grabado total,
permite lograr un grado de desmineralización de la dentina mayor con
respecto a los demás cementos utilizados en el studio. Contrariamente, los
218
cementos auto-adhesivos interactuaron con la dentina solamente de
manera limitada.
En el Capítulo 3, se presentó un enfoque basado en medida de
fuerza de adhesion y evaluaciones de microscopía electronica de barrido
de la unión entre los cementos resinosos auto-adhesivos y la dentina
hidratada. Otra vez, se utilizó como grupo control el cemento resinoso de
grabado total, cuyas caracteristicas se estudiaron de manera profunda. El
estudio reveló que la presencia de una presión pulpar puede influenciar de
manera diferente los cementos testados. Si de un lado se notó un efecto
distructivo en el cemento de paso multiple, la aplicación de una presión
pulpar durante la fase de cementación de las muestras aportó beneficios a
algunos cementos testados. Fue posible aclarar la especifica clasificación
de estos cementos, que hasta ahora se clasificaron como una clase de los
cementos resinosos. En presencia de una presión pulpar a nivel de la
superficie dentinal, algunos cementos puden ser consejados para la
cementación, mientras que algunos de estos enseňaron un comportamento
negativo: el agua, procedente de los tubulos dentinales, llega a nivel de la
interfase adhesiva y se mezcla con los monomeros resinosos todavía no
completamente polimerizados. Esta reacción puede obstaculizar la fase de
polimerización del material y consecuentemente influír negativamente en
el proceso final de adhesión. Por todo eso, durante las investigaciones en
laboratorio, una presión pulpar debería ser tomada en consideración.
A pesar de que los cementos adhesivos no requieren algun pretratamiento de la dentina, en el Capítulo 4 la atención se focalizó en la
posibilidad de poder acondicionar la superficie dental con soluciones
ácidas ligeras (0.1 M EDTA y 10% ácido poliacrílico) precedente la fase
de cementación, con el objetivo de mejorar la interacción cemento/dentina.
219
Así como revelado de los valores de fuerza de adhesión de microtensión,
los cementos auto-adhesivos testados enseňaron poseer comportamentos
adhesivos diferentes. Una mejoría de la fuerza de adhesión se vio sólo
cuando, un cemento que demonstra una tecnología parecida a aquella de
los cementos ionomero de vidrio, fue aplicado a la dentina pre-tratada con
10% de ácido poliacrílico. La coloración tricromica de Masson para la
microscopía optica, trató de individuar las caracteristicas de la interfase de
los tre cementos resinosos simplificados testados bajos las condiciones
experimentales. Se hizo encapié de que la interacción cemento/dentina fue
bastante escasa, con presencia de fibras de colageno no encapsulada al pie
de la capa hibrida, aportando nuevas dudas acerca de la efectiva capacidad
de sellado que poseen estos cementos simplificados.
En el Capítulo 5 se presentaron dos estudios basados en la
evaluación de la capacidad adhesiva de los cementos auto-adhesivos
utilizados para la cementación de postes de fibra. En el Parrafo 5.1 el
enfoque se centró en medir la fuerza de adhesión de push-out de tres
cementos auto-adhesivos para el cementado de postes de fibra en el
interno del canal radicular. Los resultados de este estudio indicaron que
hay diferencias
entre
el
potencial
adhesivo
de
los
cementos,
principalmente debido a sus diferentes composiciones químicas, que
presupone una reclasificación de sus clase de pertenencia que respecte sus
comportamentos adhesivos. Un factor que influenció de manera
predominante la fuerza de adhesión se individuó también en la modalidad
de aplicación del cemento en el espacio endodontico. En efecto, la calidad
de las interfases adhesivas puede estar negativamente afectada por el
procedimento operativo, por eso que el utilizo de un puntal elastico para la
inserción del cemento es altamente recomendable. Los distintos resultados
220
de los trabajos de investigación in vitro fueron confirmados en el Parrafo
5.2 en un estudio que trató de la durailidad de la unión cemento/poste de
fibra. Por ello, se emplearon 3 cementos auto-adhesivos de diferentes
productores, y se examinaron las fuerzas de adhesión antes y después ser
submitido a 5.000 ciclos de termociclado. Los estreses termicos no
resultaron influír negativamente en la fuerza de adhesión de RelyX
Unicem y Breeze, mientras que incluso aumentaron aquellos de G-Cem.
Una interacción química y una retención micromecanica conjuntamente
caracterizaron el mecanismo de adhesión de los cementos simplificados a
los postes de fibra. A pesar de que los fallos adhesivos a nivel de la
interfase cemento/dentina manifestaron una gran incidencia, se registró
también un alto numero de decementaciones entre cemento/poste de fibra
en todos los grupos experimentales.
En particular, la tecnología de los materiales reforzados en fibra fue
de sugerencia para el ánalisis de distintos metodos de grabado superficial
de la superficie de los postes con el objetivo de mejorar la fuerza de
adhesión. Observaciones preliminares se desarrollaron en el Capítulo 6.
Un proyecto de investigación se condujo en el Parrafo 6.1: la microscopía
confocal y la microscopía a fuerza atomica se emplearon para la
evaluación de los efectos de distintos tratamientos quimio/mecanico de la
superficie de los postes de fibra en la topografía superficial y para medir la
rugosidad de superficie. Este enfoque validó con suceso el uso del potasio
permanganato, el ethoxido de sodio y el arenado como metodos viables
para el tratamiento de superficie de los postes de fibra. Sin embargo, el
ácido hidrofluorico se reveló excesivamente agresivo, y se rescontaron
daňos de las fibras de los postes. En el Parrafo 6.2 se evaluó la influencia
de los tratamientos quimio/mecanicos de la superficie de los postes de
221
fibra sobre la fuerza de adhesión de los cementos auto-adhesivos. Para
ello, se
consideraron los tratamientos de superficie que no se
demonstraron agresivos para las fibras y los postes se cementaron
utilizandos dos materiales de cementación auto-adhesivos. El estudio no
desveló una mejoría de la fuerza de adhesión de RelyX Unicem a pesar del
tipo de tratamiento de superficies adoptado, mientras que Max-Cem trajo
beneficio de una previa aplicación de un agente silano en la superficie del
poste demonstrando un aumento de la fuerza de adhesión. De todas
formas, la intrinseca viscosidad del material fue un factor que influenció la
completa penetración del material en los espacios creados por los
tratamientos superficiales asi como se mostraron diferencias en las fuerzas
de adhesión entre los materiales de cementación utilizados. Se observó un
porcentaje inferior de defectos en la capa de aquel cemento que fue
aplicado en el canal radicular a través de un puntal elastico. Por eso, que el
utilizo de dicho puntale es recommendable clínicamente para la
introducción del material en el espacio del poste para evitar la ocurrencia
de defectos y entrapamiento de aire en el espesor del cemento.
Conclusiones
Las conclusiones y recomendaciones siguientes se pueden deducir de
las evaluaciones basicas en la evaluación de la capacidad de unión de los
cementos resinosos auto-adhesivos utilizados para el cementado de
restauraciones coronales en composites o postes de fibra:
1. Una limitada interacción caracteriza las interfases cementos autoadhesivos/dentina coronal en comparación a un cemento que
utiliza un sistema adhesivo de paso multiple. En particular, la
222
composicion química de cada producto parece influenciar el
comportamento adhesivo de los cementos testados.
2. El estado de hidratación de la dentina tiene que ser tomado en
consideración cuando se desea replicar en el laboratorio la
situation clínica de un diente vital. La presencia de un presión
pulpar a través de los tubulos dentinarios parece influenciar
negativamente el comportamento adhesivo de cementos que
utilizan adhesivos de paso multiple. Contrariamente, algunos
cementos auto-adhesivos traen beneficio de la presencia de una
presión pulpar demonstrando una reacción de fraguado simil a la
de los cementos silicato.
3. Algunas consideraciones tienen que ser hechas cuando se desea
pre-tratar la dentina con soluciones ácidas debiles antes la
aplicación de los cementos auto-adhesivos. Il tratamiento previo
de la dentina con una solución al 10% de ácido poliacrílico puede
ser conveniente antes la aplicación de G-Cem.
4. Los cementos auto-adhesivos presentan un comportamento distinto
cuando utilizados para el cementado de los postes de fibra en el
canal radicular. La modalidad de dispensación puede influír en sus
mecanismos de adhesión, y por ello que el uso de un puntal
elastico es altamente recomendable para la introducción del
cemento en el espacio del poste.
5. La simulación en laboratorio de los estreses termicos no afecta la
fuerza de adhesión de los cementos auto-adhesivos. La alta
temperatura parece favorecer la reacción de polimerización de los
cementos resinosos simplificados. Además, el mecanismo basico
223
de estos cementos, parece ser caraterizado por una interacción
química junto a una retención micromeccanica.
6. Los tratamientos superficiales que reaccionan con la matriz de
resina epoxica de los postes de fibra aumentan sus rugosidad de
superficie y mejoran el area disponibile para la adhesión a través
la creación de espacios microretentivos en la superficie de los
mismos. Entre las soluciones utilizadas, el ácido hidrofluorico ha
demonstrado de daňar excesivamente las fibras de los postes.
7. Los tratamiento de superficie de los postes de fibra no tienen
influencia en la capacidad de unión de RelyX Unicem. El
tratamiento del postes con una solución silano es recomendable
antes el utilizo de Max-Cem. De todas formas, la viscosidad del
material parece disminuír la capacidad de penetración del cemento
en las rugosidades creadas tras los tratamientos de superficie. La
adhesión a la dentina radicular se queda la mayor incertitud que
tiene que ser optimizada.
Direcciones futuras
La investigación en materia odontologica finalizada al desarrollo
de materiales ideales para la restauración de los dientes sigue desde
hace muchos aňos. Desde que fue introducido al principio de los
anňos 50, el concepto de adhesión cambiò de forma considerable,
adquiriendo un papel importante en la odontología clínica diaria y en
la investigación. El deseo de obtener resturaciones durable con
tecnicas de cementado sencillas y rapidas se considera el motivo clave
quel leva los investigadores a mejorar siempre sus conocimiento
detrás también de la continua demanda de los odontólogos clínicos y
224
de la industria. La tecnología de los materiales auto-adhesiva es, sin
duda, innovador y permite una simplificación de las tecnica de
cementación de las restauraciones indirectas. Sin embargo, algunas
limitaciones pueden confinar el utilizo clínico de estos cementos
simplificados. Mejorías deberían ser aportada al mecanismo de unión
a la dentina (coronal y radicular).
Algunas caracteristicas de los cementos auto-adhesivos deberían
ser testadas y mejoradas, como por ejemplo la viscosidad y la
contracción de polimerización. La viscosidad de estos materiales tiene
que ser reducida para alcanzar una penetración más profunda de la
resina en la dentina desmineralizada o en las restaurazione
acondicionadas. Estudios futuros deberían también evaluar el grado de
contracción de los cementos auto-adhesivos en presencia de un alto
factor C (i.e. en el conducto radicular).
Seguramente, estudios clínicos son altamente deseables para
poder validar los resultados obtenidos en esta tesi doctoral y poder
totalmente recomendar sus utilizo in vivo.
225
7.4 Zusammenfassung, Schlussfolgerungen, Zukünftige Richtungen
Der ausgwählte Zement und die Zementierung können die
Retention und die Langlebigkeit der Restaurationen beeinflussen. ZementSystemen und Zementierung-Techniken wurden weder klinisch noch
wissenschaftlich untersucht, um sie zu simplifizieren und um eine längere
Langlebigkeit der Restauration zu sichern. Die Aspekte, die im
Zusammenhang mit diesem Thema sind, sind die Bestimmung der
Verbundfestigkeit,
die
Versiegelungsfähigkeit
der
Zemente,
die
Interaktion mit dem Zahn und mit der Restauration, die Modalität der
Applikation und die mechanische Eigenschaften. Eine Simplifizierung der
Zementierung wurde durch die Einführung der selbst-adhäsiven Zemente
ermöglicht. Die selbst-adhäsiven Zemente wurden „universelle― definiert,
weil sie verschiedene Arten indirekter Restaurationen - wie Faserstifte,
Zirconia/Keramik Kronen und/bzw. Brücken, Komposit Inlays/Onlays und
Schrauben - zementieren können. Nach den Hinweisen der Firmen sollte
nur die Zementierung von Veneers vermieden werden.
In dem ersten Teil dieses Projekts (Kapitel 1) wurde eine
Einleitung über das Hauptthema der Studie dargestellt. Nach einer kurzen
Beschreibung der Zementierung-Techniken, die heutzutage für die
indirekte Restaurationen verwendet werden, wurden die Eigenschaften der
verschiedenen Zementsystemen analysiert und die selbst-adhäsiven
Zemente wurden besonders berücksichtigt. Insbesondere wurden die
Daten der Literatur über die Zementierung von Komposit Onlays,
Faserstiften bzw. Keramik Kronen mit selbst-adhäsiven Zementen
berücksichtigt. Das Ziel der selbst-adhäsiven Technologie war es, die
Zementierung zu simplifizieren und die Schwierigkeiten, die mit den
226
Multi-Step Zementsystemen im Zusammenhang sind, auszuweichen, wie
z. B. der große Einfluss der mit dem Zahnarzt korrelierenden Variabilität
und die chemische Inkompatibilität zwischen den dualhärtenden
Zementsystemen und ihren eigenen simplifizierten Adhäsiven. Die
unterschiedliche
Applikation,
der
chemische
pH-Wert
Zusammensetzung,
und
die
die
mechanischen
Modalität
der
Eigenschaften
beeinflussen die Adhäsion der simplifizierten Zemente. Insbesondere wird
die Interaktion zwischen diesen Zementen und dem Dentin immer noch
untersucht und die Forschung ist derzeit gezielt, diese Interaktion zu
verbessern. Die Zementierung von Faserstiften mit selbst-adhäsiven
Zementen wurde weder nach Thermowechselbad noch ohne ihm
untersucht und die Kombination zwischen behandelten Faserstiften und
simplifizierten Zementen wurde erforscht.
In dem zweiten Teil dieser Dissertation (Kapitel 2) wurde die
Interaktion zwischen den simplifizierten selbst-adhäsiven Zementen und
dem Dentin untersucht. Eine Studie, die mit einem Lichtmikroskop und
mit einem REM durchgeführt wurde, hat die Eigenschaften der
Schnittstelle (Demineralisation des Dentins/Durchschlagen des Zementes)
zwischen den selbst-adhäsiven Zementen und den Zementen, die Totaletch bzw. Self-etch Adhäsiven benutzen, verglichen. Unterschiede
zwischen den Materialien wurden beobachtet und es wurde gezeigt, dass
ein Total-etch System das Dentin tiefer demineralisierte. Die selbstadhäsiven Zemente haben eine begrenzte Interaktion mit dem Dentin
gezeigt.
Im Kapitel 3 wurde die Verbundfestigkeit zwischen verschiedenen
selbst-adhäsiven Zementen und durchgeschwemmtem Dentin erforscht
und REM Beobachtungen wurden auch ausgeführt. Ein Total-etch Zement
227
wurde auch in dieser Studie als Bezugsmaterial verwendet. Die
Hydratation des Dentins hat die getesteten Zemente unterschiedlich
beeinflusst. Obwohl der künstliche Druck der Pulpa einen negativen
Effekt auf den Multi-Step Zement zeigte, kann er günstig für die
Zementierung mit manchen ausgewählten selbst-adhäsiven Zementen sein.
Eine spezifische Klassierung der simplifizierten Zemente wurde
dargestellt, weil manche von denen die Eigenschaften eines Silicatähnlichen Zementes gezeigt haben. Wenn es vitales Dentin gibt, könnten
einige Zemente für die Zementierung geeigneter sein. Dagegen sollte man
aufpassen, wenn man Multi-Step Zemente verwenden möchte, weil
Wasser die adhäsive Schnittstelle durch die Dentinkanälchen erreichen
kann und die Härtung des Zementes kann gestört werden. Daher sollte ein
künstlicher hydrostatischer Druck der Pulpa während der Zementierung in
vitro berücksichtigt werden.
Auch wenn die selbst-adhäsiven Zemente keine Behandlung des
Dentins benötigen, wurde die Möglichkeit im Kapitel 4 berücksichtigt,
das Dentin bevor der Anwendung des Zementes mit milden saueren
Lösungen (0.1 M EDTA und 10% Polyacrylsäure) zu behandeln, um die
Interaktion zwischen Zement und Dentin zu verbessern. Nach den
gemessenen
Werten
der
Microtensile-Verbundfestigkeit
wurden
Unterschiede zwischen den selbst-adhäsiven Zementen entdeckt. Eine
verbesserte Adhäsion wurde beobachtet, wenn ein Glasionomer-ähnlicher
Zement auf dem mit 10% Polyacrylsäure behandelten Dentin angewendet
wurde. Die Masson-Färbung für die optische Mikroskopie hat die
Beobachtung der Eigenschaften der adhäsiven Schnittstellen von den drei
getesteten
selbst-adhäsiven
Zementen
unter
den
verschiedenen
experimentellen Bedingungen ermöglicht. Dennoch wurde eine geringere
228
Interaktion zwischen Zement und Dentin beobachtet und insbesondere
wurden ungedeckten Kollagenfasern auf dem Boden der adhäsiven
Schnittstellen gefunden. Daher macht man sich Sorgen um die echte
Versiegelungsfähigkeit der simplifizierten Zemente.
Im Kapitel 5 wurden zwei Studien über die Adhäsion zwischen
selbst-adhäsiven Zementen und Faserstiften durchgeführt. Im Paragraph
5.1 wurde die Push-out Verbundfestigkeit von drei selbst-adhäsiven
Zementen, die für die Zementierung von Epoxydharz-Faserstiften in
Wurzelkanälen verwendet wurden, bewertet. Die Ergebnisse der Studie
zeigen, dass es Unterschiede in der Adhäsion der selbst-adhäsiven
Zemente
besonders
aufgrund
ihrer
verschiedenen
chemischen
Zusammensetzungen gibt. Daher ist eine präzisere Klassierung dieser
neuen Klasse von Zementen notwendig. Die Modalität der Applikation des
Zementes in dem Post-Space wurde auch für einen wichtigen Faktor, der
die Ergebnisse beeinflusste, gehalten. Die Qualität der adhäsiven
Schnittstelle kann von der Modalität der Applikation beeinflusst werden,
deswegen ist die Anwendung von einer Verlängerungskanüle ratsam, um
den Zement ins Post-Space anzubringen. Die verschiedenen Hinweise, die
aus den Ergebnissen der vorhergehenden Studie folgen, wurden im
Paragraph 5.2, in dem ein Test der Langlebigkeit durchgeführt wurde,
bestätigt. Drei verschiedenen selbst-adhäsiven Zemente wurden für die
Zementierung von Faserstiften angewendet und ihre Verbundfestigkeit
wurde weder bevor noch nach 5.000 Zyklen im Thermowechselbad
bewertet. Diese Studie zeigte, dass der thermische Stress die
Verbundfestigkeiten von RelyX Unicem und Breeze nicht beeinflusste,
dagegen erhöhte er die Verbundfestigkeit von G-Cem. Eine Kombination
zwischen chemischen Interaktionen und mikromechanischen Retentionen
229
scheint den Mechanismus der Adhäsion zwischen selbst-adhäsiven
Zementen und Faserstiften zu charakterisieren. Obwohl die Häufigkeit von
adhäsiven Brüchen zwischen Zement und Dentin relevant war, gab es
Dezementierungen
zwischen
Zement
und
Faserstift
in
allen
experimentellen Gruppen.
In der Technologie der Faser-verstärkten Materialien wurde es
geraten, verschiedene Behandlungen von der Oberfläche der Faserstifte zu
untersuchen, um eine zuverlässige Adhäsion zu erreichen. Eine Serie von
Präliminarbeobachtungen wurde im Kapitel 6 dargestellt. Eine Studie
wurde durchgeführt und sie wurde im Paragraph 6.1 dargestellt. Die
Confocal Mikroskopie und die Raster-Kraft Mikroskopie wurden
kombiniert, um die Effekte verschiedener chemischen und mechanischen
Behandlungen von der Oberfläche der Stifte auf ihre oberflächlichen
Topographien und auf ihren Mittelrillenabstand zu bewerten. Nach dieser
Technik schienen die Anwendungen von Kaliumpermanganat bzw.
Natriumethoxyd
und
das
Behandlungen
besonders
Rillenabstand,
der
von
Sandstrahlen
wirksam
der
zu
partiellen
zwischen
sein:
der
den
getesteten
oberflächliche
Entfernung/Auflösung
der
Epoxydharzmatrix erhöht wurde, könnte die adhäsive Oberfläche durch
Mikroretentionen verbessern. Dagegen wurde die Anwendung von
Fluorwasserstoffsäure für eine zu aggressive Behandlung gehalten, weil
sie den Quarzfasern zu viel schadete. Im Paragraph 6.2 wurde der
Einfluss von der Behandlung der Oberfläche des Faserstiftes auf die
Retention
von
Zementen
in
Epoxydharz-Faserstiften,
Wurzelkanälen
zementiert
die
mit
wurden,
selbst-adhäsiven
berücksichtigt.
Unschädliche chemische und mechanische Behandlungen der Oberfläche
der Faserstifte und zwei selbst-adhäsiven Zemente wurden verwendet. Die
230
Behandlungen der Oberfläche haben die Retention von Faserstiften, die
mit RelyX Unicem zementiert wurden, nicht verbessert. Dagegen wurde
die Verbundfestigkeit von Max-Cem durch die Anwendung eines Silans
optimiert. Allerdings scheint die Viskosität der Materialien das komplette
Durchschlagen der Zemente in die Mikroretentionen, die von den
Behandlungen der Oberfläche der Faserstifte verursacht wurden, zu
behindern. Unterschiede zwischen den Zementen wurden auch gefunden.
Ein geringerer Prozentsatz von Defekten wurde beobachtet, wenn eine
Verlängerungskanüle verwendet wurde, um den Zement ins Post-Space
anzubringen.
Die
Anwendung
von
spezifisch
geeigneten
Applikationsmitteln ist stark zu empfehlen, um Defekte und Luftblasen in
dem Zement zu vermeiden.
Schlussfolgerungen
Die folgende Schlussfolgerungen können aus den Laborstudien, die
die
Adhäsion
verschiedener
selbst-adhäsiven
Zemente
für
die
Zementierung von Komposit-Restaurationen bzw. Faserstiften bewertet
haben, gezogen werden:
1)
Verglichen mit Total-etch bzw. Self-etch Systemen
charakterisiert eine begrenzte Interaktion mit dem Dentin die
Adhäsion der selbst-adhäsiven Zemente. Insbesondere beeinflusst
die
chemische
Zusammensetzung
jedes
Produktes
seinen
Mechanismus von Adhäsion.
2)
Die Hydratation des Dentins sollte
für die
Restauration eines vitalen Zahnes berücksichtigt werden. Der
ständige Strom des Wassers durch die Dentinkanälchen kann die
Adhäsion der Zemente beeinflussen; insbesondere kann er für
231
Zemente, die Multi-Step Adhäsiven benötigen, schädlich sein.
Dagegen ist der Strom des Wassers günstig für die selbstadhäsiven Zemente, weil sie eine ähnliche Härtung wie die SilicatZemente haben.
3)
Man sollte Betrachtungen darüber anstellen, wenn
man das Dentin bevor der Zementierung von indirekten
Restaurationen mit selbst-adhäsiven Zementen mit milden saueren
Lösungen behandelt. Die Behandlung des Dentins mit 10%
Polyacrylsäure bevor der Anwendung von besonderen selbstadhäsiven Zementen kann geraten werden.
4)
Es gibt Unterschiede in der Adhäsion verschiedener
selbst-adhäsiven Zemente, die für die Zementierung von
Faserstiften in Wurzelkanälen angewendet wurden. Die Modalität
der Applikation beeinflusst den Mechanismus von Adhäsion und
die Anwendung einer Verlängerungskanüle ist notwendig, um
Defekte in dem Zement zu vermeiden.
5)
Adhäsion
Das Thermowechselbad hat keinen Einfluss auf die
der
getesteten
selbst-adhäsiven
Zemente.
Eine
verbesserte Härtung kann wegen der erhöhten Temperatur
vermutet werden. Eine Kombination zwischen chemischen
Reaktionen und mikromechanischen Retentionen charakterisiert
die Adhäsion zwischen den selbst-adhäsiven Zementen und den
Faserstiften.
6)
Behandlungen
der
Oberfläche,
die
mit
der
Epoxydharzmatrix des Faserstiftes selektiv reagieren, erhöhen den
Rillenabstand und sie verbessern die adhäsive Oberfläche durch
Mikroretentionen ohne der Struktur der Quarzfasern zu schaden.
232
7)
Behandlungen der Oberfläche von Faserstiften
verbessern nicht die Retention, wenn die Stifte mit selbstadhäsiven Zementen zementiert werden. Die Viskosität der
Materialien behindert ihres komplette Durchschlagen in die
Mikroretentionen, die von den Behandlungen der Oberfläche der
Faserstifte
verursacht
werden.
Die
Adhäsion
mit
dem
Wurzeldentin ist immer noch ein „heißes Thema― und sie musst
noch optimiert werden.
Zukünftige Richtungen
Die zahnmedizinische Forschung, die auf die Entwicklung idealer
Materialien zielt, dauert seit vielen Jahren. Seit ihrer Einführung in den
späten Fünfzigerjahren hat die Adhäsion eine große Entwicklung gehabt
und ihre Rolle in der Alltagspraxis und in der zahnmedizinischen
Forschung ist wichtiger geworden. Der Wunsch eine langlebige
Restauration durch eine einfache und zeitsparende Zementierung zu
erreichen ist der Grund für die ständigen Forderungen der Zahnärzte und
der Firmen von Zahnmaterialien und er bringt die Forscher dazu, ihre
Ideen ständig zu entwickeln. Die selbst-adhäsive Technologie ist ohne
Zweifeln innovativ und sie ermöglicht eine simplifizierte Zementierung.
Allerdings
können
manche
Grenzen
ihre
klinische
Anwendung
beschränken. Innovationen des Mechanismus von Adhäsion mit dem
Dentin (Kronendentin und Wurzeldentin) sollten gemacht werden.
Manche Eigenschaften der selbst-adhäsiven Zemente bezüglich der
Viskosität und des Schrumpfung-Stress sollten verbessert und getestet
werden. Techniken, die auf die Senkung der großen Viskosität der
Materialien zielen, sind notwendig, um ein tieferes Durchschlagen des
233
Resins in die demineralisierte Zahnhartsubstanz bzw. in die behandelte
Restauration zu ermöglichen. Zukünftige Studien sollten den Prozentsatz
der Schrumpfung der simplifizierten Zemente bei einem großen C-Faktor
(z. B. in dem Wurzelkanal) bewerten.
Es gibt keine Zweifel daran, dass klinische Untersuchungen stark
nötig sind, um die Ergebnisse der Laborstudien zu bestätigen und um die
klinische Anwendung dieser Zemente zu empfehlen.
234
7.5 Résumé, conclusions et Directions futures
Le ciment et la procédure de scellement choisis peuvent influencer la
rétention et la pérennité des restaurations prothétiques. Les matériaux et
techniques de scellement ont été largement étudiés que ce soit sur le plan
clinique ou expérimental dans le but de les simplifier tout en maintenant la
longévité de la prothèse. Les problèmes liés à ce sujet comprennent
l’évaluation de la force d’adhésion, l’efficacité des ciments en tant
qu’agents de scellement, l’interaction avec les substrats dentaires et les
restaurations, et les modalités de mise en place et les propriétés
mécaniques. Une simplification des procédures de scellement est
intervenue avec l’introduction des ciments autoadhésifs. Les ciments
autoadhésifs ont été définis comme ―universels‖ puisqu’ils sont capables
de coller différents types de restaurations indirectes comme les tenons en
fibres, les couronnes ou bridges en zircone ou céramique, les inlays/onlays
en composite, et les tenons vissés. Selon les fabricants, seul le scellement
des facettes est à proscrire.
Le chapitre 1 constitue une introduction du sujet principal. Apres
une courte description des procédures contemporaines de scellement des
restaurations indirectes, ce chapitre analyse en détail les caractéristiques
des ciments en se penchant plus précisément sur ceux des systèmes
autoadhésifs. En particulier, les données disponibles dans la littérature
concernant l’efficacité du collage des onlays composites, des tenons en
fibres, et des couronnes céramiques par des résines autoadhésives est
analysée. L’objectif des technologies autoadhésives est de simplifier les
procédures de collage et de surmonter les difficultés liées au systèmes
comprenant plusieurs étapes, tels que la haute influence de la variabilité
235
liée à l’operateur ou l’incompatibilité chimique qui intervient lors de
l’utilisation de ciments auto/photo polymérisant avec leur systèmes
adhésifs simplifies. Toutefois, les différences dans la composition
chimique, les modalités de mise en place, le pH, et les propriétés
mécaniques influent sur le mécanisme de collage des ciments simplifies.
En particulier, l’interaction entre ces ciments et le substrat dentinaire et
toujours à l’étude, et la recherche se focalise à présent sur l’amélioration
du collage à ce niveau. La capacité des ciments autoadhésifs à sceller les
tenons en fibres a également été étudiée avec et sans thermocyclage et la
possibilité de combiner un prétraitement de ces tenons avec des ciments
simplifies a également été analysée.
Dans la seconde partie de ce travail (Chapitre 2), l’étude a plus
particulièrement analysé l’interaction entre les ciments autoadhésifs
simplifies et le substrat dentinaire. Une étude d’observation basée sur la
microscopie optique et électronique à balayage a permis de comparer les
caractéristiques des interfaces (en termes de déminéralisation/pénétration
de la dentine) des ciments autoadhésifs et des ciments résines qui utilisent
des adhésifs automordançants, ou multi systèmes (également appelés totaletch). Des différences entre les matériaux ont été identifiées démontrant
que les systèmes dits « total-etch » étaient capables de déminéraliser le
substrat dentinaire en profondeur. Les ciments autoadhésifs ne se sont
révélés capables que d’une interaction limitée avec la dentine.
Dans le Chapitre 3, l’évaluation de la force d’adhésion et une étude
par microscopie électronique à balayage de différents ciments autoadhésifs
à de la dentine perfusée a été réalisée. De même, un ciment résine « totaletch » a été utilisé comme référence. Le niveau d’hydratation de la dentine
influence de façon différente les ciments testés. Bien qu’ayant un effet
236
préjudiciable sur le ciment « total-etch », la présence de pression pulpaire
peut être bénéfique lors du collage à l’aide de certains ciments
autoadhésifs. Une classification plus spécifique des ciments résines
simplifiés a été établie parce que certains d’entre eux ont démontrés des
caractéristiques similaires aux ciments simili-silicates. En présence de
dentine vitale, certains ciments pourraient être conseillés pour les
procédures de collage, alors que des précautions doivent être prises lors de
l’utilisation de ciments « total-etch » en raison de la percolation d’eau à
travers les tubuli dentinaires qui peut atteindre l’interface d’adhésion et
compromettre une polymérisation adéquate du ciment proprement dit. Il
semble. En ce sens, il est évident que la simulation de la pression
hydrostatique intra-pulpaire est requise lors des tests in vitro des
procédures de collage.
Bien que les ciments autoadhésifs de nécessitent pas de prétraitement
de la dentine, le Chapitre 4 porte l’attention sur la possibilité du
conditionnement du substrat dentinaire à l’aide de solutions acides faibles
(0.1M EDTA and 10% polyacrylic acid) avant l’application du ciment
dans le but d’améliorer l’interaction ciment/dentine. Selon les forces
microtensiles enregistrées, des différences dans les capacités de collage
des ciments autoadhésifs ont été détectées. Une amélioration de l’adhésion
a été enregistrée lorsqu’un ciment autoadhésif, qui présentent des
similarités aux ciments verres-ionomères, a été utilisé pour sceller à de la
dentine mordançée à l’aide d’acide polyacrylique a 10%. La technique
coloration de Masson en microscopie optique a permis d’individualiser les
caractéristiques
interfaciales
des
3
ciments
autoadhésifs
testés
expérimentalement. Toutefois, de rares interactions dentine/ciment ont été
observées, et en particulier des fibres de collagène exposées on été
237
trouvées au fond des interfaces adhésives, ce qui a renouvelé les craintes
concernant la capacité proprement dite de scellement des ciments résine
simplifiés.
Dans le Chapitre 5, deux études basées sur l’évaluation des
performances de collage de ciments autoadhésifs ont été réalisées. Dans le
Paragraphe 5.1, les forces de push-out de 3 ciments autoadhésifs utilisés
pour sceller les tenons en fibres et matrice en résine époxy à la dentine
radiculaire ont été évaluées. Les résultats des études indiquent que des
différences peuvent être détectées entre les mécanismes de collage des
ciments résines autoadhésifs particulièrement en raisons de leurs
compositions chimiques différentes, ce qui rend nécessaire une
classification en profondeur de cette nouvelle classe de ciments résine. Le
mode d’application du ciment à l’intérieur de l’espace canalaire a
également été considéré comme un facteur important conditionnant les
résultats obtenus. La qualité de l’interface adhésive peut être affectée par
la procédure opératoire, ainsi l’utilisation d’un embout d’élongation est
conseillée pour mettre le ciment dans le logement du tenon. Les
différentes indications dérivant des résultats ci dessus ont trouvé
confirmation dans le Paragraphe 5.2, dans lequel un test de pérennité a
été réalisé. Trois ciments résines autoadhésifs commerciaux ont été utilisés
pour sceller des tenons en fibres et leurs forces d’adhésion ont été
mesurées avant et après avoir été soumis à 5000 cycles de vieillissement
thermique. Cette étude a révélé que les stress thermiques n’ont pas affecté
les valeurs de « push-out » de RelyC Unicem ou de Breeze, alors que
celles de G-Cem ont été augmentées. Une combinaison d’interactions
chimiques et de rétentions micromécaniques a semblé caractériser le
mécanisme d’adhésion des ciments adhésifs aux tenons en fibres. Bien que
238
l’incidence des fractures adhésives à l’interface ciment/dentine ait été
significative, un décollement à l’interface ciment/tenon a été observé dans
tous les groupes expérimentaux.
Plus précisément, la technologie des matériaux renforcés par fibres a
suggéré de tester différents traitements de surface des tenons dans le but
d’améliorer la rétention. Une série d’observations préliminaires a été
effectuée dans le Chapitre 6. Une recherche a été menée et décrite dans le
Paragraphe 6.1: des évaluations par microscopie confocale et à force
atomique ont été combinées afin d’évaluer les effets des différents
traitements de surface chemomécaniques des tenons en fibres sur la
topographie et la rugosité de leur surface. Cette approcha a validé
l’utilisation de permanganate de potassium, d’éthoxyde de sodium, et du
sablage parmi les différentes méthodes de traitement de la surface des
tenons : l’augmentation de la rugosité de surface a travers la
dissolution/retrait de la matrice en résine époxy augmenterait la surface
disponible à l’adhésion par la création d’espaces microrétentifs.
Inversement, l’acide hydrofluorhydrique a été considéré comme une
méthode de conditionnement agressive causant des dommages sévères aux
fibres de quartz. Dans le Paragraphe 6.2, l’influence des traitements
superficiels des tenons en fibres sur la force d’adhésion des résines
autoadhésives utilisées pour le scellement les tenons en fibres à matrice
époxy dans l’espace canalaire a été étudié. Des méthodes de
conditionnement chemomécaniques non destructives ont été adoptées pour
traiter les tenons en fibres et 2 ciments autoadhésifs ont été utilises. Le
conditionnement de surface des tenons n’a pas amélioré la rétention de
RelyX Unicem aux tenons en fibres alors qu’il s’est avéré être un bénéfice
supplémentaire pour Max-Cem après application d’un agent de couple
239
type silane afin d’optimiser la force d’adhésion. Toutefois, la viscosité des
matériaux utilisés a semblé limiter la pénétration des ciments dans les
micro espaces générés par les méthodes de conditionnement. Des
différences ont également été trouvées entre les ciments de scellement. Un
moindre pourcentage de défauts a été observé lorsqu’un embout
d’élongation était utilisé pour mettre le ciment en place à l’intérieur du
logement du tenon. L’utilisation d’aides au placement est hautement
conseillée afin de limiter les possibilités de défauts ou d’emprisonnement
d’air au sein de la masse de ciment.
Conclusions
Les conclusions suivantes peuvent être tirées à partir des études
expérimentales basées sur l’évaluation du potentiel d’adhésion de
différents ciments résines autoadhésifs utilises dans le collage de
restaurations coronaires composites et/ou de tenons en fibres :
1) Une interaction limitée avec la dentine caractérise l’adhésion des
résines autoadhésives en comparaison avec les systèmes adhésifs
dits « total-etch ». Plus particulièrement, La composition chimique
de chaque produit possède une influence sur la capacité
d’adhésion.
2) Le niveau d’hydratation de la dentine devrait être pris en
considération lors de la restauration de dents vitales. Le flot
continu d’eau à travers les tubuli dentinaires peut influencer
l’efficacité du collage des ciments, en particulier il peut être
néfaste à ceux utilisant des systèmes multi étapes. A l’inverse, il
peut être postulé que les ciments autoadhésifs mettent à profit la
240
transsudation hydrique dans une réaction de prise similaire à celles
des ciments silicates.
3) Certaines considérations devraient être prises en compte lors du
traitement de la dentine par des solutions acides faibles avant le
scellement de restaurations indirectes à l’aide de ciments
autoadhésifs. Le mordançage de la dentine par de l’acide
polyacrylique à 10% pourrait être proposé avant l’utilisation de
certains ciments autoadhésifs.
4) Des différences existent entre le potentiel adhésif de différents
ciments résines autoadhésifs utilises pour sceller des tenons en
fibres à l’intérieur de l’espace canalaire. Le mode de placement du
ciment affecte le mécanisme d’adhésion et l’utilisation d’un
embout d’élongation est nécessaire afin d’éviter tout défaut au sein
de la masse du ciment.
5) Le vieillissement thermique n’affecte pas le potentiel d’adhésion
des ciments autoadhésifs testés. Une réaction de prise améliorée est
postulée en présence de hautes températures. Une combinaison de
réactions chimiques et de retentions micromécaniques caractérise
l’adhésion des ciments autoadhésifs au tenons en fibres.
6) Les procédures de conditionnement de surface qui réagissent
sélectivement avec la matrice époxy du tenon en fibre améliorent
la rugosité et augmente la surface disponible pour l’adhésion en
créant des espaces de micro rétention sans affecter la structure
interne du tenon. L’acide fluorhydrique affecte la texture
superficielle des fibres de quartz.
7) Les traitements de surface des tenons en fibres n’améliorent pas la
rétention des ciments résines autoadhésifs. La viscosité des
241
matériaux empêche leur pénétration dans les micro espaces créés
par les modalités de prétraitement. L’adhésion à la dentine
demeure un sujet « chaud » qui nécessite une optimisation.
Directions futures
La recherche dentaire qui vise à développer des matériaux idéaux
dure depuis des années. Depuis son introduction dans la fin des années 50,
l’adhésion a subi une maturation considérable, augmentant son rôle dans la
pratique quotidienne et la recherche dentaire. Le désir d’obtenir des
restaurations prothétiques à longue pérennité en utilisant des procédures de
collages simples et rapides représente la force motrice derrière la quête
continue des cliniciens et des fabricants dentaires et pousse les chercheurs
à développer de nouveaux concepts continuellement. La technologie
autoadhésive est sans doute innovatrice et ouvre la voie à une procédure
de collage simplifiée. Toutefois, de nombreuses limitations viennent
modérer leurs applications cliniques. Des innovations devraient viser le
mécanisme d’adhésion à la dentine coronaire et radiculaire.
Certaines caractéristiques des ciments autoadhésifs, en termes de
viscosité ou de stress de contraction, devraient être améliorées et testées.
Des techniques conçues pour réduire la viscosité élevée des matériaux sont
nécessaire afin d’améliorer leur pénétration dans la dentine déminéralisée
ou au niveau des surface restauratrices prétraitées. De nouvelles études
devraient également évaluer le pourcentage de contraction des résines
simplifiées en présence d’un facteur de contraction élevé (i.e. dans le canal
radiculaire).
242
Il ne fait aucun doute que des études cliniques sont hautement
requises pour valider les résultats obtenus expérimentalement et permettre
de recommander ces produits en clinique.
243
7.6 Resumo, Conclusões, Futuras perspectivas
O material de cimentação selecionado e os procedimentos de
cimentação podem influenciar a manutenção e durabilidade das
restaurações protéticas.
Materiais de cimentação e técnicas têm sido
amplamente investigados tanto na prática clínica e na pesquisa de tentar
simplificá-los, assegurando certa longevidade da restauração protética. As
questões relacionadas com este tema incluem a avaliação da resistência de
união, a eficácia dos cimentos como agentes de vedação, a interação com
o substrato dental e as restaurações, a modalidade de injeção e
propriedades
mecânicas.
A
simplificação
dos
procedimentos
de
cimentação foi possível com a introdução de cimentos auto-adesivos.
Cimentos resinosos auto-adesivos foram definidos como "universal",
como eles podem cimentar diferentes tipos de restaurações indiretas, tais
como pinos de fibra, zircônia / coroa de cerâmica e / ou pontes, inlays
composto / onlays e parafusos. Segundo alegações dos fabricantes,
somente facetas devem ser evitada a cimentação.
Na parte inicial deste projeto (Capítulo 1), uma introdução do tema
principal do estudo foi apresentada. Após uma breve descrição dos
procedimentos de cimentação hoje disponíveis para a cimentação de
restaurações indiretas, a introdução foi profundamente para analisar as
características de sistemas de cimento, com incidência nos de autocimentação de resina adesiva. Em particular, os dados disponíveis na
literatura sobre a eficácia da ligação de cimentos auto-adesivos usada para
onlays, pinos de fibra ou coroas de cerâmica foram analisados. O objetivo
de cimentos auto-adesivos foi o de simplificar os procedimentos de
244
cimentação e superar as dificuldades relacionadas com o cimento de
sistemas multi-passo, como a influência de alta variabilidade do operador
e da incompatibilidade química que pode ocorrer quando utilizar agentes
cimentantes de presa dupla com os seus sistemas adesivos simplificados.
No entanto, as diferenças na composição química, modalidade de inserção,
pH e propriedades mecânicas influenciam o mecanismo de união dos
cimentos simplificado. Em particular, a interação entre esses e os cimentos
para a dentina ainda é uma questão de estudo e investigação estando agora
centrada em melhorar esta ligação local. A capacidade de auto-cimentos
adesivos para cimentação pinos de fibra também foi considerado com e
sem teste de envelhecimento térmico, bem como a possibilidade de
combinar previamente tratada pinos com os cimentos simplificado foi
analisada.
Na segunda parte desta tese (Capítulo 2), o estudo foi concentrado
para analisar profundamente a interação entre os cimentos adesivos auto
simplificado e substrato dentina. Um estudo de microscopia óptica e
microscopia eletrônica de varredura permitiu a comparação das
características interfaciais (em termos de desmineralização de dentina /
penetração de resina) de cimentos auto-adesivos e cimentos resinosos que
utilizam um total-etch e um auto-adesivo . As diferenças foram
encontradas entre os materiais, mostrando que um cimento de
condicionamento total foi capaz de desmineralizar profundamente o
substrato dentina. Cimentos auto-adesivos mostraram uma capacidade
apenas limitada para interagir com a dentina. No capítulo 3, resistência de
união e microscopia eletrônica de varredura avaliações de diferentes
cimentos auto-adesivos à dentina
foram avaliados. Novamente, um
cimento de condicionamento total foi utilizado para comparações. O
245
diferente estado de hidratação da dentina influenciou os cimentos testados.
Embora tenha um efeito negativo sobre o cimentos de multi-passos, a
presença de pressão pulpar pode ser benéfico durante a cimentação de
cimentos auto-adesivos. A classificação mais específica dos cimentos
simplificados foi feita, como alguns deles apresentam características
semelhantes de presença de silicato. Na presença de dentina vital,
cimentos, poderiam ser aconselhável para os procedimentos de
cimentação, ao passo que deve ser dada atenção ao usar cimentos
resinosos multi-etapas, já que a água pode permear através dos túbulos
dentinários, atingindo as interfaces adesivas e dificultar uma reação
adequada fixação do cimento em si. Nestes termos, a simulação de uma
pressão hidrostática intra pulpar deve ser tomado em consideração
adequando a realização de procedimentos de cimentação in vitro.
Embora a auto-cimentos adesivos não necessitam de pré-tratamentos
da dentina, no capítulo 4, a atenção foi dada a possibilidade de
condicionar o substrato dental com leve soluções ácidas (0,1 M de EDTA
e ácido poliacrílico 10%) antes da aplicação do cimento, a fim de melhorar
as interações cimento / dentina. De acordo com a resistência à microtração
as diferenças no desempenho da ligação dos auto-cimentos adesivos foram
encontrados. A aderência melhorou quando um cimento auto-adesivo, que
mostrou-ionômero de vidro-como em sua composição, foi cimentado em
dentina condicionada por 10% de ácido poliacrílico. A técnica de
coloração de Masson para microscopia óptica permitiu individualizar as
características interfaciais dos três cimentos auto-adesivos testados sob as
condições experimentais. No entanto, escassa interação de cimento /
dentina foi observada, e, em particular, fibras colágenas expostas foram
encontrados no fundo da interfaces do adesivo o que renova as
246
preocupações quanto à efetiva capacidade de vedação dos cimentos
resinosos simplificados.
No capítulo 5, dois estudos com base na avaliação do desempenho
da ligação dos cimentos auto adesivos para pinos de fibra foram
realizadas. No tópico 5.1 testes de push-out de três cimentos auto-adesivos
utilizados para cimentação de pinos de fibra de resina epóxica a dentina
radicular foram avaliados. Os resultados do estudo indicam que as
diferenças podem ser encontradas entre o mecanismo de ligação dos
cimentos resinosos auto-adesivos, principalmente devido às suas
diferentes composições químicas, que tornam necessária uma classificação
profunda desta nova classe de cimentos resinosos. O modo de aplicação do
cimento no espaço do pino também foi considerado um fator importante
que influencia os resultados obtidos. A qualidade da interface adesiva
pode ser afetada pelo procedimento clinico, portanto, o uso de um
alongamento da ponta é aconselhável para a colocação do cimento no
espaço do pino. As várias conclusões provenientes dos resultados do
estudo descrito anteriormente foram encontradas confirmações no topico
5.2, em que a durabilidade teste foi realizada. Três diferentemente
cimentos auto-adesivos foram utilizados para pinos de fibra a forca de
união foi avaliada antes e após serem submetidos a 5.000 ciclos de
envelhecimento térmico. Este estudo revelou que o estresse térmico não
afetou os valores fde orça de push-out bond do RelyX Unicem e Breeze,
enquanto aumentaram os de G-Cem. Uma combinação de interações
químicas e micro-retenções mecânicas parecem caracterizar o mecanismo
de adesão de cimentos auto-adesivos aos pinos de fibra. Embora a
incidência de falha adesiva cimento / dentina lado era relevante,
247
―decimentações‖ na interface cimento / pino de fibra ocorreu em todos os
grupos experimentais.
Mais precisamente, a tecnologia de material reforçado com fibra
gerou a sugestão para o pós-teste de diferentes tratamentos superficiais do
pino de fibra com o objetivo de obter uma adesão efetiva.
Uma série de observações preliminares foram conduzidos no
Capítulo 6. A pesquisa foi realizada e descrita no § 6.1: avaliações de
microscopia confocal e microscopia de força atômica foram combinados
para avaliar os efeitos de diferentes pós tratamentos químico / mecânico da
superfície do pino de fibra na topografia de sua superfície e rugosidade da
superfície. Esta abordagem validou com sucesso o uso permanganato de
potássio, sódio e jateamento para tratar a superfície do pino entre os
procedimentos testados:o aumento da rugosidade da superfície através da
remoção parcial / dissolução da matriz de resina epoxícas melhorou a área
de superfície disponível para a adesão através da criação de micro-espaços
retentivos. Por outro lado, o ácido fluorídrico foi considerado um método
de condicionamento agressivo, como ele causou danos excessivos das
fibras de quartzo. No ponto 6.2, a influência dos tratamentos superficiais
da fibra sobre a resistência retentiva dos cimentos resinosos auto-adesivos
utilizados para cimentação de pinos de resina epóxicas a dentina radicular
foi considerada. Abordagens não destrutivas químico / mecânicas foram
adotadas para o tratamento de pinos de fibra e dois cimentos auto adesivos
foram utilizados. Condicionamentos de superfície do pino não melhorou a
retenção de RelyX Unicem aos pinos de fibra, enquanto Max-Cem obteve
um adicional benefício da aplicação de um agente de silanizador para
otimizar a força de adesão. No entanto, a viscosidade do material parece
dificultar a penetração total dos cimentos nos micro-espaços criados pelo
248
condicionamento. Diferenças também foram encontradas entre os agentes
de cimentação. Uma percentagem inferior de defeitos foi detectada quando
uma ponta alongada foi utilizado para colocar o cimento no espaço. A
utilização de aparelhos de aplicação é altamente recomendável para limitar
a ocorrência de defeitos e aprisionamento de ar na massa de cimento.
Conclusões
As seguintes conclusões podem ser tiradas com base nas pesquisas
laboratoriais na avaliação do potencial de ligação de diferentes cimentos
auto adesivos utilizados para a cimentação de restaurações em compósito e
/ ou pinos de fibra:
1) A interação limitada com dentina caracteriza o comportamento da
ligação do auto-cimentos resinosos a adesiva quando comparado a um
total-etch ou sistemas de auto-adesivo . Em particular, a composição
química de cada produto influencia o seu mecanismo de adesão.
2) O estado de hidratação da dentina deve ser levado em
consideração quando a restauração de um dente vital. O contínuo fluxo de
fluido através dos túbulos dentinários pode influenciar a eficácia da adesão
de cimentação cimentos, em particular, pode ser prejudicial para cimentos
que utilizam sistemas adesivos de vários passos. Por outro lado, a
cimentos resinosos auto-adesivos, levam os benefícios da transudação da
água como uma reação semelhante à definição de cimentos de silicato
pode ser postulada.
3) Considerações devem ser feitas quando a o pré-tratamento da
dentina com soluções ácidas antes da cimentação de restaurações indiretas
com cimentos auto-adesivos. O condicionamento da dentina com ácido
poliacrílico 10% pode ser proposta antes de usar o cimento auto-adesivo.
249
4) Existem diferenças entre o potencial de ligação de cimentos autoadesivos utilizados para cimentação de pinos de fibra em dentina radicular.
A modalidade de dispensa afeta seu mecanismo de ligação e utilização
uma ponta alongada se faz necessária para evitar qualquer defeito dentro
da massa de cimento.
5) Envelhecimento térmico não afetar o potencial de ligação
cimentos resinoso auto-adesivos. Uma reação melhorada é especulada na
presença de altas temperaturas. Uma combinação de reações químicas e
micro-retenções mecânicas caracterizam o vínculo de cimentos autoadesivos para os pinos de fibra.
6) Os processos de condicionamento da seletivo da superfície que
reagem com a matriz de resina epóxi do pino de fibra para aumentar e
melhorar a rugosidade da superfície disponível para a adesão através da
criação de micro-espaços retentivos sem afetar a estrutura interna do pino.
Ácido fluorídrico afeta a textura superficial de fibras de quartzo.
7) Tratamentos da superfície de pinos de fibra não melhoram a
retenção de cimentos resinosos auto-adesivos aos mesmos. A viscosidade
dos materiais dificulta a sua penetração no micro-espaços criados na
superfície após as modalidades de condicionamento. A adesão à dentina
radicular continua a ser um tema "quente" que precisam ser otimizados.
Futuras perspectivas
Investigações odontológicas orientadas para o desenvolvimento de
materiais ideais tem estado em curso há muitos anos. Desde a sua
introdução no final dos anos 50, a adesão tem tido considerável maturação,
aumentando o exercido na prática diária e investigação dental. O desejo de
obter uma proservação duradoura da prótese com simples e práticos
250
procedimentos de cimentação é uma força motriz por trás da busca
contínua de odontológos e fabricantes o que leva os investigadores a
desenvolver continuamente seus pensamentos. A tecnologia de autoadesão é sem dúvida inovador e aponta a um procedimento simplificado
de cimentação. No entanto, muitas limitações podem limitar o seu uso
clínico. As inovações devem ser realizadas no mecanismo de adesão à
dentina (coronal e radicular).
Algumas características de cimentos auto-adesivos, em termos de
viscosidade ou tensão de contração, devem ser melhoradas e testadas.
Técnicas destinadas a reduzir a elevada viscosidade dos materiais, a fim de
promover uma profunda penetração da resina no tecido dental
desmineralizado ou para o tecido condicionado. Estudos futuros deverão
avaliar também o percentual de contração dos cimentos resinosos
simplificados na presença de um alto fator C (ou seja, no canal de raiz).
Não há dúvidas de que os estudos clínicos são altamente necessárias,
a fim de validar os resultados da investigação e validar se esses cimentos
são clinicamente recomendáveis.
251
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Curriculum Vitae
Dr. Claudia Mazzitelli
Date of birth: February 5th, 1980
Place of birth: Lamezia Terme
Civil status: Unmarried
Citizenship: Italian
Home address: via Timavo, 13, Lamezia Terme (CZ), 88046
Telephone number: +393383152058
E-mail address: [email protected]
[email protected]
[email protected]
2003: Degree in Dentistry, University of Siena, Siena, Italy.
Research activity
2005: PhD Program in ―Biotechnologies: section of Dental Biomaterials‖,
University of Siena;
2006: Master of Science in ―Dental Biomaterials‖, University of Siena;
2006/2008: two year scholarship for research activity at the School of
Dentistry of the University of Granada, Spain;
2008: Diploma de Estudios Avanzados, PhD Program in ―Adhesión
Odontología‖, University of Granada;
2008: PhD in ―Adhesión en Odontología‖, University of Granada.
285
Professional positions
2003-2009: Internship at the Department of Restorative Dentistry,
University of Siena;
2003-2009: Internship at the Department of Mobile Prosthodontics,
University of Siena;
2004- Private Practice, General Dentist;
2008-2009; Internship at the Department of Prosthodontics and Dental
Materials, University of Siena;
2007-2009: Professor for practice of Prosthodontics III at the University of
Siena, Italy.
Membership in Dental Societies:
2005-2006: Member of SIDOC (Italian Society of Restorative Dentistry);
2006: Member of EPA (European Prosthodontics Association)
2007-2009: Member of ADM (Academy of Dental Materials);
2007-2009: Member of IADR (International Association of Dental
Research).
International publications
Mazzitelli C, Ferrari M, Toledano M, Osorio E, Monticelli F, Osorio R.
Surface roughness analysis of fiber post conditioning processes. Journal of
Dental Research 2008; 87: 186-190.
Papacchini F, Magni E, Radovic I, Mazzitelli C, Monticelli F, Goracci C,
Polimeni A, Ferrari M. Effect of intermediate agents and pre-heating of
repairing resin on composite-repair bond. Operative Dentistry 2007; 32:
363-371.
286
Mazzitelli C, Magni E, Radovic I, Papacchini F, Goracci C, Ferrari M.
The adhesion between FRC posts and resin core materials: a microtensile
bond strength test following different treatments of the post surface.
International Dentistry of South Africa 2007; 9: 30-40.
Magni E, Mazzitelli C, Papacchini F, Radovic I, Goracci C, Coniglio I,
Ferrari M. Adhesion between fiber posts and resin luting agents: a
microtensile bond strength test and an SEM investigation following
different treatments of the post surface. Journal of Adhesive Dentistry
2007; 9: 195-202.
Mazzitelli C, Monticelli F, Toledano M, Ferrari M, Osorio R. Effect of
thermocycling on the bond strength of self-adhesive cements to fiber
posts. Clinical Oral Investigations, in press.
Mazzitelli C, Monticelli F, Osorio R, Casucci A, Toledano M, Ferrari M.
Effect of simulated pulpal pressure on self-adhesive cements bonding to
dentin. Dental Materials 2008; 24: 1156-1163.
Radovic I, Mazzitelli C, Chieffi N, Ferrari M. Evaluation of the adhesion
of fiber posts cemented using different adhesive approaches. European
Journal of Oral Sciences 2008; 116: 57-563.
Monticelli F, Osorio R, Mazzitelli C, Ferrari M, Toledano M. Limited
decalcification/diffusion of self-adhesive cements into dentin Journal of
Dental Research 2008; 87: 974-979.
287
Casucci A, Osorio E, Osorio R, Monticelli F, Toledano M, Mazzitelli C,
Ferrari M. Influence of different surface treatments on surface zirconia
frameworks. Journal of Dentistry 2009; 37: 891-897.
Cantoro A, Goracci C, Papacchini F, Mazzitelli C, Fadda GM, Ferrari M.
Effect of pre-cure temperatures on the bonding potential of self-etch and
self-adhesive resin cements. Dent Mater 2008; 24: 577-83.
Schiavetti R, Garcia-Godoy F, Mazzitelli C, Barlattani A, Ferrari M,
Osorio R. Comparison of fracture resistance of bonded glass fiber posts at
different lengths. American Journal of Dentistry, in press.
Mazzitelli C, Monticelli F, Toledano M, Ferrari M, Osorio R. Dentin
treatment effects on the bonding performance of self-adhesive resin
cements. European Journal of Oral Sciences, in press.
Mazzitelli C, Monticelli F. Evaluation of the push-out bond strength of
self-adhesive resin cements to fiber posts. International Dentistry of South
Africa, in press.
Mazzitelli C, Papacchini F, Monticelli F, Toledano M, Ferrari M. Effects
of post surface treatments on the bond strength of self-adhesive cements.
American Journal of Dentistry, in press.
Magni E, Radovic I, Coniglio I, Papacchini F, Mazzitelli C. Bonding of
self-etching adhesive/flowable composite combinations to enamel and
288
dentin: A microtensile bond strength evaluation. International Dentistry of
South Africa, 2007; 9: 6-18
Giovannetti M, Casucci A, Casucci D, Mazzitelli C, Borracchini A.
Phonetic analysis and maxillary anterior teeth position: a pilot study on
preliminary outcomes. International Dentistry of South Africa 2009; 11:
32-39.
Abstracts
Mazzitelli C, Monticelli F, Osorio R, Casucci A, Toledano M, Ferrari M.
Water sorption and solubility of different self-adhesive cements. ADM
Wurzburg 2007, October 2-4, Abstract #101.
Casucci A, Mazzitelli C, Monticelli F, Osorio R, Toledano M, Ferrari M.
Retention of self-adhesive cements on pre-treated epoxy-based fiber posts.
ADM Wurzburg 2007, October 2-4, Abstract #208.
Monticelli F, Mazzitelli C, Casucci A, Osorio R, Toledano M, Ferrari M.
Bond strengths of self-adhesive cements to fiber-reinforced posts. ADM
Wurzburg 2007, October 2-4, Abstract #137.
Stranieri M, Casucci A, Mazzitelli C, Geminiani A, Borracchini A. A
smile analysis of a population 0f 80 subjects from 20 to 25 years old. EPA
London 2006, Novemeber 2-4, Abstract #90.
289
Casucci A, Geminiani A, Mazzitelli C, Sedda M, Borracchini A. Anterior
teeth position: prosthetic implant treatment starting point. EPA London
2006, November 2-4, Abstract #101.
Casucci A, Casucci D, Mazzitelli C, Borracchini A. Phonetic analysis in
complete venture and fixed-implant prosthesis wearers. ICP Fukuoka
2007, September 10-13, Abstract #301.
Mazzitelli C, Monticelli F, Osorio R, Casucci A, Toledano M, Ferrari M.
Simulated pulpal pressure influences self-adhesive cements bonding to
dentin. IADR Thessaloniki 2007, Semptember 26-29, Abstract #467.
Monticelli F, Osorio R, Mazzitelli C, Ferrari M, Toledano M. Interfacial
characteristics of self-adhesive cements bonded to dentin. IADR
Thessaloniki 2007, September 26-29, Abstract #209.
Mazzitelli C, Toledano M, Monticelli F, Chieffi N, Ferrari M, Osorio R.
Interfacial evalautions of self-adhesive cements bonded to conditioned
dentin. IADR Miami 2008, April 2-5, Abstract #657.
Monticelli F, Osorio R, Toledano M, Mazzitelli C, Papacchini F, Ferrari
M. Simulated pulpal pressure influences self-etch adesive bonding to
dentin. IADR PEF London 2008, September 10-12, Abstract #60.
Mazzitelli C, Monticelli F, Casucci A, Toledano M, Osorio R, Ferrari M.
Bonding effectiveness of self-adhesive cements to perfused dentin. IADR
PEF London 2008, September 10-12, Abstract #56.
290
Schiavetti R, Mazzitelli C, Casucci A, Toledano M, Osorio R, Barlattani
A, Ferrari M. The effect of post length on the fracture resi stance of
endodontically treated teeth. IADR PEF London 2008; September 10-12,
Abstract #64.
Toledano M, Mazzitelli C, Monticelli F, Ferrari M, Osorio R. May surface
pre-treatments improve self-adhesive cements bonding to dentin? IADR
PEF London 2008; September 10-12, Abstract #55.
Radovic I, Mazzitelli C, Chieffi N, Ferrari M. Adhesion of fiber posts
cemented using different adhesive approaches. IADR Miami 2008, July
10-12, Abstract #123.
Mazzitelli C, Monticelli F, Casucci A, Toledano M, Osorio R, Ferrari M.
Bond strength of self-adhesive cements to fiber-reinforced posts prior and
after thermocycling. Conseuro Sevilla 2009, March 13-15, Abstract #107.
Casucci A, Papacchini F, Mazzitelli C, Osorio E, Toledano M, Osorio R,
Borracchini A, Ferrari M. Zirconia surface pre-treatments: a combined
AFM and SEM analysis. Conseuro Sevilla 2009, March 13-15, Abstract
#99.
Cantoro A, Goracci C, Papacchini F, Mazzitelli C, Fadda MG, Ferrari M.
Bonding potential of pre-heated self-etch and self-adhesive resin cements.
IADR Thessaloniki 2007, Semptember 26-29, Abstract #102.
291
Mazzitelli C, Porciani PF, Grandini S, Ferrari M. Pilot study for evaluation
of different procedures in post-space cleaning and their effect on adhesion.
III International meeting, Conseuro. Rome, February 10-12, 2006;
Mazzitelli C, Vano M, Cury AH, Goracci C, Chieffi N, Gabriele M,
Ferrari M. Retention of different type of fibre posts luted at different
intervals obturated using a eugenol sealer. III International meeting,
Conseuro. Roma, February 10-12, 2006.
Monticelli F, Osorio R, Mazzitelli C, Toledano M. Effect of surface
sealants on marginal seal of composite restorations. IADR-CED Munich
2009, September 10-12, Abstract #104.
Mazzitelli C, Monticelli F, Papacchini F, Ferrari M. Self-adhesive cements
bonding: influence of dispensing methods and dentin hydration. IADRCED Munich 2009, September 10-12, Abstract #126.
Casucci A, Mazzitelli C, Papacchini F, Monticelli F, Osorio E, Osorio R,
Toledano M, Ferrari M. Surface treatment effects on three zirconiumoxide ceramics. IADR-CED Munich 2009, September 10-12, Abstract
#140.
Chieffi N, Mazzitelli C, Sedda M, Van Noort R, Ferrari M. Effect of
admixed microspheres on mechanical properties of a cement. IADR-CED
Munich 2009, September 10-12, Abstract #273.
292
Casucci A, Mazzitelli C, Papacchini F, Osorio E, Borracchini A,
Giovannetti M, Ferrari M. Surface treatments effect on Lava zirconiumoxide ceramic. ICP Cape Town 2009, September 10-12, Abstract #85.
Oral Presentations
Mazzitelli C. Static and dynamic smile analysis. 16th International
Congress of Dentistry, Syrian Dental Association 2007, Damascus,
September 4-6.
Mazzitelli C. Impression materials in
fixed prosthodontics. 5th
International Meeting of Scientific Dentistry, University of Aleppo,
Aleppo 2007, April 27-29.
Mazzitelli C. Impresión en prótesis fija: el originador para un éxito
óptimo. 2th event Vita in Vita, Mexico City 2007, October 4-5.
Mazzitelli C.
Impresión en prótesis fija: el originador para un éxito
óptimo. 30° Anniversary FAM Dental, Morelia 2007, October 3-6.
Borracchini A, Mazzitelli C. Tratamientos de casos complejos con y sin
implantes. Jornada Avance de las XVII Jornadas Internacionales APA
―Protesis 2008‖, Buenos Aires 2008, May 16.
Mazzitelli C. Impresiones en protesis fija: el punto de partida para un caso
exitoso. Aniversario E.B. Pareja Lecaros SA, Lima 2008, May 21.
293
Mazzitelli C. Impresiones en protesis fija: el punto de partida para un caso
exitoso. Santiago del Cile 2008, May 19.
Borracchini A, Casucci A, Geminiani A, Mazzitelli C, Stranieri M. A
smile analysis of population of 80 sunjects from 20 to 25 year old. EPA
London 2006, November 2-4.
Borracchini A, Casucci A, Geminiani A, Mazzitelli C, Sedda M. Anterior
teeth position: prosthetic implant treatment starting point. EPA London
2006, November 2-4.
Borracchini A, Stranieri M, Mazzitelli C, Casucci A. Dynamic smile
analysis in 80 subjects from 20 to 25 year old: averages and correlations.
12° ICP Fukuoka 2007, September 5-8.
Borracchini A, Casucci D, Casucci A, Mazzitelli C. Prosthetic
reconstruction and phonetic. EPA Athen 2007, October 11-13.
National Publications
Mazzitelli C, Goracci C, Grandini S, Ferrari M. Polimerizzazione e
materiali dentari a confront. Doctor Os 2006; 17: 1-9.
Magni E, Mazzitelli C, Cantoro A, Coniglio I, Cagidiaco MC, Ferrari M.
Indagini microscopiche e forza di adesione di cementi self-adhesive su
dentina radicolare. Doctor Os 2007; 18: 1-4.
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Abstracts
Cantoro A, Mazzitelli C, Goracci C, Papacchini F, Ferrari M. Effetto del
pre-riscaldamento sull’adesione di cementi resinosi auto mordenzanti e
autoadesivi. SIDOC Rome 2007; February 15-17, Abstract #15.
Mazzitelli
C,
Monticelli
F, Osorio
R, Osorio
E, Ferrari M.
Condizionamento superficiale di perni in fibra: AFM e microscopia
confocale. XI congresso nazionale SIDOC, Roma, 15-17 Febbraio 2007.
Giovannetti M, Casucci A, Mazzitelli C, Borracchini A. Analisi fonetica
in protesi totale: influenza del montaggio dei denti frontali. Collegio dei
Docenti Roma 2009, April 22-26, Abstract #304.
Mazzitelli C, Monticelli F, Chieffi N, Osorio R, Toledano M, Ferrari M.
Influenza della pressione pulpare sulla forza di unione di cementi resinosi
auto-adesivi alla dentina. Collegio dei Docenti Roma 2009, April 22-26,
Abstract #137.
Mazzitelli C, Monticelli F, Chieffi N, Toledano M, Osorio R, Ferrari M.
Può l’acido poliacrilico migliorare l’interazione tra cementi auto-adesivi e
la dentina? Collegio dei Docenti Roma 2009, April 22-26, Abstract #199.
Casucci A, Mazzitelli C, Papacchini F, Monticelli F, Osorio E,
Borracchini A, Ferrari M. Analisi morfologica di tre tipi di zirconia
sottoposti a differenti trattamenti di superficie. Collegio dei Docenti Rome
2009, April 22-26, Abstract #163
295
Acknowledgements
This thesis is respectifully submitted to Prof. Silvano Focardi, Rector of
the University of Siena, to Prof. Gian Maria Rossolini, Dean of the Faculty
of Medicine of the University of Siena, to Prof. Marco Ferrari, Director of
the Department of Dental Science, Dean of School of Dental Medicine,
Director of the PhD Program in ―Biotechnologies: section of Dental
Biomaterials‖ University of Siena. It is also submitted to Prof. Francisco
González Lodeiro, Rector of the University of Granada, to Prof. Alberto
Rodríguez Archilla, Director of the Department of ―Estomatología‖ of the
Faculty of Dentistry of the University of Granada. This research has been
carried out in the Department of Fixed Prosthodontics and Dental
Materials of the University of Siena (Italy) and in the Department of
―Estomatología‖ of the University of Granada (Spain).
I wish to express my sincere gratitude and admiration to my Promoter
Prof. Marco Ferrari for the possibility he gave me to come in touch with
the research world. This thesis could not have been written without him
who not only served as my supervisor but also encouraged and challenged
me throughout my academic program. I would also aknowledge Prof.
Manuel Toledano and Prof. Raquel Osorio who guided me through the
dissertation process, never accepting less than my best efforts. A special
thank goes to Prof. Francesca Monticelli, for the time she spent for me and
the support I found both in my Italian and Spanish experiences. Everytime
she was there supporting me and spending good words.
I’m indebeted to my congress-mates: Dr. Federica Papacchini, Dr Elisa
Magni and Dr. Gabriele Corciolani for the humanity they showed to
possess. Great travellers and great persons, who taught me to continue to
296
fight and resist to the difficulties of life (when you burn your hand, remove
it from the fire). I’ll never forgot our experiences and how much we
enjoyed even during working missions.
I would also like to mention my colleagues, with whom I shared my
doctoral experience and clinical knowledges: Dr. Ivan Coniglio, for our
long talking break; Dr. Nicoletta Chieffi, for the time she spent listening at
me and advicing me; Prof. Cecilia Goracci, for her scientific suggestions;
Prof. Simone Grandini, for the friendship will ever have; Prof. Alessandro
Vichi, for his encouraging ―Buongiorno!!‖ of every thursday morning; Dr.
Remo Schiavetti, with whom I shared my Spanish experience (no hagas
hoy lo que puedes hacer maňana); Dr. Ziad Salameh, for his funny
attitude. Great thanks to Dr. Pamela Fatighenti for her secretarial (and not
only) support and to the people that helped me with the translation: Dr.
Elisa Magni (German), Dr Carlos Augusto Ramos de Carvalho
(Portuguese), Dr. Hani Ounsi (French). My gratitude goes also to Prof.
Andrea Borracchini, he has been the great brother and friend, listening to
my complains and problems, but also encouraging my happy moments.
I would like to thank all my family. I dedicate my work, with deepest
respect and gratitude to my parents and to my sister, for their support,
sacrifices and prayers. I love them forever, and I am incapable to show
them how much.
My deep appreciation to all my friends (they know who) who were beside
me in all situations, supporting, praying, applauding and enjoying with
me. I would dedicate this paragraph to the people who were there: ―The
only force significant enough to facilitate our act of creation seems to be
desire, or as Charles Fourier called it, PASSION (Amsterdam, 2009)”.
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