How to use Thermafil successfully Clinical

Clinical
How to use
Thermafil successfully
Wilhelm Pertot advises practitioners on how to
maximise their results when using the
Thermafil obturation technique
I
n 1978, WB Johnson described a
technique for the obturation of root
canals with thermoplasticised gutta
percha. A few years later, the T h e rm a fi l
device was introduced by Tulsa Dental. In
its current version, the Thermafil obturator,
which is available in the UK from DentsplyMaillefer (01932 853422), features a
flexible plastic carrier coated with alpha
phase gutta percha. The obturator is carried
into a special oven with a
temperature and time control.
The heated gutta percha
becomes thermoplasticised
and the obturator is then
inserted into the root canal to
the working length.
Over the years, this fast
obturation system, which
combines a short learning
curve with a short working
time, length control and
Wilhelm Pertot DCD, DEA,
sealability, has proven to be
PhD graduated from St
very popular among general
Joseph University Dental
practitioners, as well as
School, Lebanon, in 1988.
among specialists.
In 1991, he earned a
master in endodontics
from Marseille Dental
School and obtained his
PhD in 1996.
He was nominated
assistant professor in
1991, promoted to senior
lecturer in 1994 and
served as co-director for
the postgraduate
programme in endodontics
in Marseille Dental School
from 1992 to 1998.
Wilhelm has been actively
involved in clinical
research in different fields
of endodontics and has
lectured and run hands-on
courses extensively, both
nationally and
internationally
Advantages of the
Thermafil
technique
Like all filling techniques,
the Thermafil technique
requires good canal shape
with a consistent and
continuous taper from the
apical constriction to the
coronal orifice.
The Thermafil technique
offers many advantages,
including:
• Shortness of learning curve
• Speed of clinical
application
• Apical control of fill
• Conservative enlargement
of root canal (when
Figure 1: (top to bottom) The Thermafil obturator, the corresponding
nickel titanium Verifier and the plastic car rrier from which gutta percha
has been removed
Figure 2: Thermafil plastic carrier from which gutta percha has been
removed. Note the longitudinal groove which facilitates retreatment if
needed
compared to other warm gutta percha
compaction techniques)
• Three-dimensional obturation and apical
sealing ability.
Description of the material
and the technique
The Thermafil Plus system features several
components:
• The Thermafil obturator. This is 25mm in
length, and is a tapered, highly flexible,
plastic carrier coated with a low molecular
weight alpha phase gutta percha, from size
20 to size 140 (Figure 1). The plastic
carrier features a longitudinal groove along
its complete length to facilitate retreatment
(Figure 2)
• The Thermafil verifiers. These are .04
taper nickel titanium hand instruments,
which are used to check the taper of the
canal and select the proper obturator
(Figure 1)
• The Thermaprep oven. This allows
uniform, predictable and controlled heating
Endodontic Practice May 2000
Clinical
of the gutta percha, by allowing precise
temperature and time control (Figure 3)
• The Thermacut burs. These feature a
smooth non-cutting round head, which is
used to sever the plastic carrier without
any risk of perforation. These burs are
available in 4 sizes: .010, .012, .014 and
.016 (Figure 4)
• The post-space burs. These are long
special non-cutting burs, which are used to
prepare the space for the dowel post. These
burs are available in two sizes (005 and
007), and two lengths (25mm and 31mm)
Importance of the canal
shape
The Thermafil technique is a combination
of different f illing techniques. On insertion
of the obturator, the tapered plastic carrier
allows the practitioner to exert both lateral
and vertical compaction forces on heated
gutta percha.
The shape of the prepared root canal is
clearly of paramount importance. A
tapered funnel-form preparation is
indispensable, not only to achieve a well
cleaned root canal system but also to allow
its three-dimensional obturation. The use
of rotary nickel titanium instruments is
recommended (ProFile or Greater Taper
rotary f iles), because they ideally prepare a
continuously tapered shape, with a
controlled apical diameter.
Nervertheless, it should be noted that
less coronal enlargement is needed with
the Thermafil technique than with other
warm vertical gutta percha compaction
techniques (vertical compaction or System
B), which require more elimination of
coronal dentine structure to allow
prefitting of the pluggers. This is even
more obvious in severely curved and long
canals, in which the high flexibility of the
plastic carrier enables the T h e rm a fi l
obturator to f it easily at the working length
(Figure 5).
Figure 3: The Thermaprep oven, is used to warm Thermafil obturators
Gauging the canal
preparation
After cleaning and shaping have been
completed, a verifier corresponding in size
to the last instrument used to the working
length is used to gauge the canal. The
verifier should slide easily, without any
contact with the canal walls, and should fit
passively in its last 1mm, with soft friction
at the working length.
If the verifier is blocking between
0.5mm and 1mm from the working length,
it may be used in a rotary motion to
enlarge this portion of the canal.
Alternatively, a smaller verifier may be
tested and should usually fit easily to the
working length. The corresponding
Thermafil obturator is then used to achieve
obturation of the canal. This method relies
on the adjustment of the obturator silicone
stop at the working length to control
penetration and avoid overextension of the
plastic carrier into the periapical tissues.
Another interesting and reliable method,
is based on the use of a Thermafil plastic
carrier from which the gutta percha has
been removed (Figure 1). As the gutta
percha extends 1mm beyond the tip of the
carrier, the Thermafil obturator to be used
would be the one corresponding in size to
the plastic carrier that blocks at working
length or between 0.5mm and 1mm from
the working length (Figure 6). In order to
Figure 4: The Thermacut bur, which is used to sever the Thermafil obturator, features a smooth non-cutting
round head and is available in 4 sizes (.010, .012, .014 and .016)
Endodontic Practice May 2000
Clinical
Figure 5: The flexibility of the plastic carrier allows insertion of the Thermafil obturator to the apical
terminus of severely curved canals. The canals were shaped using ProFile instruments
avoid direct contact between the carrier
and the canal walls during obturation,
the test carrier should only bind at its
tip, without any lateral contacts. This
leaves enough room laterally for the
gutta percha and sealer. In this instance,
overextension of the plastic carrier is
highly unlikely, if not impossible.
Filling procedure
The Thermafil obturator should be
dipped in a sodium hypochlorite
solution for at least one minute to
ensure its decontamination (Glickman,
1992). In the mean time, the canal is
dried with paper points and root canal
sealer is prepared. The manufacturer
recommends the use of the paste-paste
epoxy resin-based root canal sealer
(Topseal, Dentsply-Maillefer; AH plus,
Dentsply). Because of its relatively fluid
consistency, this sealer should be used
carefully and only in very small
amounts. Thus, to avoid extrusion of
excess sealer in the periapical tissues,
only the coronal third of the canal is
coated with a small amount of sealer
using a paper point. Other sealers, such
as Kerr’s Root Canal Sealer, may also
be used (Kerr UK). In that case, care
should be taken to avoid a very thick
mix which could prevent the obturator
being inserted to the desired length.
The obturator is placed into the oven,
which allows homogenous heating of
the gutta percha at the exact
temperature. Heating time varies from
15 to 45 seconds, depending on
obturator size, and is regulated
automatically. No prewarming of the
oven is required.
When the obturator is ready for use,
it is pulled out from the oven and
inserted directly into the canal using a
slow, firm and continuous apical
movement (Figure 7) .
As it moves apically, the diameter of
the tapered plastic carriers increase,
thereby exerting more hydraulic lateral
pressure (wedging effect) on
thermoplasticised gutta percha and
sealer (Figures 8a and 8b).
The obturator is stabilised using light
f inger pressure to limit shrinkage of the
gutta percha while cooling. At that
point, an X-ray might be taken to ensure
placement of the Thermafil obturator at
the correct working length (Figures 6d
and 10c). The coronal gutta percha
around the plastic carrier is compacted
using hand pluggers.
The shaft of the obturator is then cut
off at the canal orifice using a
Thermacut bur (Figures 9 and 10).
Endodontic Practice May 2000
Figure 6a: Preoperative X-ray of a lower
first molar requiring an endodontic
treatment
Figure 6b: X-ray of the working length
control. The canals were shaped using
ProFile instruments
Figure 6c: X-ray of the plastic carriers used for
gauging of the canal and choice of the Thermafil
obturator
Figure 6e:
Postoperative
X-ray of the
completed
case
Figure 6d: X-ray
upon insertion of
the Thermafil
obturators. The
distal canal was
filled using a size
.35 obturator, and
size .25 was used
in the mesial
canals. The
obturator in the
mesio-lingual
canal has not
been cut-off yet
Problems and solutions
Pain upon insertion of the obturator
Sometimes, the insertion of the T h e rm a fi l
obturator might result in pain for the
patient. This is usually due to air
compression into the periradicular tissues.
Slow insertion of the obturator and, in
some cases, administration of local
anesthesia would avoid such a problem.
Overfilling and overextension
As for all obturation techniques that rely
on gutta percha compaction, the Themafil
obturation technique might result in
overfilling of the gutta percha and/or the
sealer. Overfilling results from gutta
percha or sealer extrusion in the
periapical tissues. Mixing the sealer at
the correct consistency, the use of only
a small amounts of sealer and slow
insertion of the Thermafil obturator at
the correct working length should avoid
this problem.
Overextension results from the
extension of the Thermafil plastic
carrier in the periapical tissues. This is
caused by using a Thermafil obturator
with a diameter smaller than the apical
diameter of the preparation and not
checking the working length. This
generally results in an incomplete apical
seal and might be avoided by a perfectly
tapered preparation and by the selection
of the proper obturator. As explained
earlier, the proper Thermafil obturator
Endodontic Practice May 2000
Clinical
should be chosen according to the carrier
binding at or between 0.5mm and 1mm
from the working length. This would make
it impossible for the plastic carrier to be
pushed past the binding point.
Direct contact between the plastic
carrier and the wall of the canal
In some cases, when the canal is long,
curved and/or improperly shaped, the
plastic carrier might come into direct
contact with the canal wall without gutta
percha or sealer in position. If this
phenomenon occurs apically, this might
lead to lack in sealability (Barkins &
Montgomery, 1992; Juhlin et al, 1993).
This can be avoided by giving the canal the
adequate continuous tapered shape and by
choosing the correct Thermafil obturator,
as described earlier.
Obturation of large and elliptic canals
Single rooted premolars (upper and lower),
lower incisors, and mesial and distal canals
of lower molars often show elliptical or
ribbon-like coronal shapes, while the crosssection tends to be round towards the apex.
Thus, in the coronal areas, the compaction
pressure exerted by the plastic carrier alone
might prove to be inadequate to allow
complete flow of gutta percha and sealer
into the irregularities. To allow adequate
filling of the coronal portion of the root
canal system, the gutta percha around the
carrier is compacted using Pierre
Machtou’s hand pluggers (DentsplyMaillefer).
Occlusion of the openings of other canals
in multirooted teeth upon elimination of
the carrier and of excess of gutta percha
The obturator is designed with excess gutta
percha to accomodate large canals. Thus,
upon insertion of the obturator in relatively
small canals in multirooted teeth, sealer
and gutta percha will usually flow back and
accumulate at the orifice. This might lead
to obscuring access to other canals.
Moreover, severing of the obturator at that
point might lead to projection of debris
into the other canals. To prevent these
phenomena, excess gutta percha should be
trimmed off the shaft using a scalpel blade
before heating, and a paper point or small
cotton pellet might be placed into
the orifice of the other canals.
Preparation of a dowel space
Some authors prefer to postpone
the dowel space preparation to
allow complete setting of the
sealer. Nevertheless, this
procedure might prove
indispensable, especially aesthetics
are concerned or when a
temporary crown must be adjusted.
Several studies (Rybicki and
Zillich, 1994; Saunders et al,
1993) have shown that the apical
seal of the Thermafil is
undisturbed if the dowel space is
prepared immediately after
obturation.
After trimming the handle of
the Thermafil carrier at the orifice
of the canal, preparation of a
dowel space might prove difficult or
might lead to the retrieval of the entire
plastic carrier. This is usually due to the
use of a drill that is too small in size,
which slides alongside the T h e rm a fi l
carrier. To avoid this problem, the
selected drill should be the largest drill
fitting inside the coronal portion of the
prepared canal. Using the selected drill at
high speed is often sufficient to allow
removal of excess carrier and gutta percha
and preparation of the dowel space.
In a recent paper, Cantatore & Cochet
(1998) proposed a modification of the tip
of the Thermacut bur to allow its
insertion deep into the canal. High speed
rotation without water spray would
produce enough frictional heat to soften
the plastic and the gutta percha, thus
enabling removal of excess carrier and
gutta percha.
Recently, a new bur, the Post Space bur
(Dentsply-Maillefer) has become
available. This bur, which features a long
non-cutting head is used at high speed
without water spray, to produce frictional
heat and to soften the plastic and the
gutta percha. Once the desired portion of
the Thermafil obturator has been
eliminated, the shape of the free space is
refined according to the reconstruction
technique.
Endodontic Practice May 2000
Figure 7: The
Thermafil obturator
is inserted into the
root canal to
working length,
using a slow, firm
and continuous
apical movement
Clinical
Figure 8a and b: As the Thermafil obturator is pushed apically, the tapered plastic carriers excert more
lateral pressure on the heated gutta percha and sealer, thus allowing obturation of lateral canals.
Here, the simulated canal was filled using Thermafil without sealer and gutta percha was pushed to
the full extent of the lateral canal
Figure 9: After
insertion, the
Thermafil obturator
is maintained using
finger pressure and
cut-off with a
Thermacut bur
Retreatment
The conventional method for T h e rm a fi l
retreatment relies on the use of a gutta
percha solvent which will allow insertion
of a hand instrument between the plastic
carrier and the canal wall.
The presence of the longitudinal groove
in the plastic carrier allows easier
insertion of the hand instrument.
Whatever the solvent, different studies
have shown that the maximum time
needed for Thermafil retreatment never
exceeds six to seven minutes (Ibarrola et
al, 1993; Wilcox and Juhlin, 1994;
Bertrand et al, 1997). However, the best
available technique for T h e rm a fi l
retreatment today relies on the use of a
rotary nickel titanium instrument after
using a
solvent for
softening
the gutta
percha. The
use of
orifice
shapers size
3 (size 40,
.06 taper) or
2 (size 30,
.06 taper)
would then
allow a
ProFile size
25, .06 taper
to penetrate
into the canal alongside the plastic
carrier. The nickel titanium instrument is
advanced toward the apex using an inand-out pecking motion, and, at one
point, will completely pull-out the plastic
carrier from the canal.
Conclusion
Thermafil is an easy, reliable and
efficient technique, which allows
practitioners to obtain three-dimensional
root canal fillings with warm gutta
percha in a minimum amount of time
(Becker & Donnelly, 1997).
Nevertheless, one should bear in mind
that excellent results can only be
obtained if the root canal system has
been thoroughly cleaned and given the
proper shape.
References
Barkins W and Montgomery S (1992).
Evaluation of Thermafil obturation in curved
canals prepared by the Canal Master-U system.
J Endo 18: 285-9
Becker TA and Donnelly JC (1997). T h e rm a fi l
obturation : a literature review. Gen Dent 45:
46-55
Bertrand MF, Pellegrino JC, Rocca JP,
Klinghoffer A and Bolla M (1977). Removal of
Thermafil root canal filling material. J Endo
23: 54-7
Endodontic Practice May 2000
Figure 10a : Preoperative X-Ray of a mandibular molar adressed for
retreatment
Figure 10b: X-Ray of the working length control. The canals were
shaped using the ProFile instruments
Figure 10c: X-Ray upon insertion of the Thermafil obturators
Figure 10d: View of the access cavity after sectionning of the
obturators
Figure 10e and 10f: Postoperative X-Rays of the completed case
Cantatore G and Cochet JY (1998). The
Thermafil System. Endo 17: 35-49.
Ibarrola JL, Knowles KI and Ludlow MO (1993).
Retrievability of Thermafil plastic cores using
organic solvents. J Endo 19: 417-8
Saunders WP, Saunders EM, Gutmann JL and
Gutmann ML (1993). An assessment of the
plastic Thermafil obturation technique. Part 3.
The effect of post space preparation on the
apical seal. Int Endod J 26: 184-9
Johnson WB (1978). A new gutta-percha
technique. J Endo 4: 184-188
Rybicki R and Zillich R (1994). Apical sealing
with Thermafil following immediate and
delayed post space preparation. J Endo 20: 64-6
Juhlin J, Walton R and Dovgan J (1993).
Adaptation of the Thermafil components to
canal walls. J Endo 19: 130-5
Wilcox LR and Juhlin JJ (1994). Endodontic
retreatment of Thermafil versus laterally
condensed gutta percha. J Endo 20: 115-7
Endodontic Practice May 2000