Effects of laser irradiation on machined implant surface

Effects of Laser Irradiation on Machined and
Anodized Titanium Disks
Ji-Hye Park, DDS, MSD1/Seong-Joo Heo, DDS, MSD, PhD2/Jai-Young Koak, DDS, MSD, PhD2/
Seong-Kyun Kim, DDS, MSD, PhD3/Chong-Hyun Han, DDS, MSD, PhD4/Joo-Hee Lee, DDS, MSD, PhD5
Purpose: Although the laser has become one of the most commonly used tools for implant dentistry,
research is lacking on whether or not the laser causes any changes on the surface of titanium (Ti) implants.
The present study analyzed the morphology, composition, crystal structure, and surface roughness changes
of machined and anodized Ti surfaces, irradiated with erbium chromium–doped yttrium-scandium-galliumgarnet (Er,Cr:YSGG), erbium-doped yttrium-aluminum-garnet (Er:YAG), and carbon dioxide (CO2) lasers.
Materials and Methods: Seventy-two Ti disks were fabricated by machining commercially pure Ti (grade 3);
36 of them were anodized at 300 V. The disks were irradiated with Er,Cr:YSGG, Er:YAG, and CO2 lasers at five
different powers (1, 2, 3, 4, and 5 W). The irradiated disks were examined with scanning electron microscopy,
electron probe microanalysis, x-ray diffractometry, and optical interferometry. Results: Surface changes
were observed on both types of Ti surfaces irradiated with the Er,Cr:YSGG laser when more than 3 W of
power were applied. Surface changes were observed on both types of Ti surfaces when irradiated with the
Er:YAG laser with more than 2 W of power. No change was observed when the disks were irradiated with the
CO2 laser. The proportion of oxide in the machined Ti disk increased after the application of the Er,Cr:YSGG
or Er:YAG laser. In the anodized Ti disk, the anatase peak intensity decreased and the rutile peak intensity
increased after laser irradiation. The irradiated Ti disks were significantly rougher than the nonirradiated Ti
disks. Conclusions: The Er:YAG and Er,Cr:YSGG laser resulted in surface changes on the Ti disks according
to the power output. The CO2 laser did not affect the surface of the Ti disks, irrespective of the power output.
Int J Oral Maxillofac Implants 2012;27:265–272
Key words: anodic oxidation, crystal structure, laser, roughness, surface composition, titanium disk
L
asers have been used frequently in the field of dentistry. Because of various advantages in ablation, decontamination, and hemostasis, laser treatment has been
1Clinical
Lecturer, Department of Prosthodontics and Dental
Research Institute, School of Dentistry, Seoul National
University, Seoul, South Korea.
2Professor, Department of Prosthodontics and Dental
Research Institute, School of Dentistry, Seoul National
University, Seoul, South Korea.
3Associate Professor, Department of Prosthodontics and
Dental Research Institute, Seoul National University Dental
Hospital, School of Dentistry, Seoul National University,
Seoul, South Korea.
4Professor, Department of Prosthodontics, Yongdong
Severance Dental Hospital, College of Dentistry, Yonsei
University, Seoul, South Korea.
5Assistant Professor, Department of Prosthodontics, Asan
Medical Center, College of Medicine, University of Ulsan,
Seoul, South Korea.
Correspondence to: Prof Seong-Kyun Kim, Department of
Prosthodontics and Dental Research Institute, Seoul National
University Dental Hospital, School of Dentistry, Seoul National
University, 28 Yeongun-dong, Chongno-Gu, Seoul, 110-749,
South Korea. Fax: +82-2-2072-3860. Email: [email protected]
expected to serve as an alternative or adjunct to conventional dental therapy.1–5 Carbon dioxide (CO2) and
neodymium-doped yttrium-aluminum-garnet (Nd:YAG)
lasers are recommended for soft tissue ablation, so they
have been used primarily for soft tissue management in
periodontics and oral surgery.6,7 Erbium lasers, including
both erbium chromium-doped yttrium-scandium-gallium-garnet (Er,Cr:YSGG) and erbium-doped yttriumaluminum-garnet (Er:YAG) lasers, have been used for
ablating both soft and hard tissues.8,9
Lasers are useful in implant placement surgery,
stage-two implant surgery, and treatment of periimplantitis.1,2 Lasers have been used to modify the surface of dental implants or to decontaminate exposed
implant surfaces.7,10–12 A previous study showed that irradiation of titanium (Ti) disks with a CO2 or Er,Cr:YSGG
laser could induce osteoblast proliferation and differentiation.13 To date, however, there is disagreement
regarding whether direct application of a laser causes
changes to Ti disks, and if so, what the effect of laser power is on the surface. Romanos et al14 showed
that a diode laser had no effect on Ti disks, although a
Nd:YAG laser, operated at a low power, damaged them.
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Park et al
Table 1 Laser Devices and Parameters Used
in This Study
Laser type/
power
Energy
(mJ/pulse)
Energy fluency
(Jcm–2/pulse)
Air/water
Er,Cr:YSGG
1 W
2 W
3 W
4 W
5 W
50
100
150
200
250
17.7
35.4
53.1
70.7
88.4
10
15
20
25
30
Er:YAG
1 W
2 W
3 W
4 W
5 W
50
100
150
200
250
25.5
50.9
76.4
101.9
127.3
10
15
20
25
30
CO2
1 W
2 W
3 W
4 W
5 W
50
100
150
200
250
25.5
50.9
76.4
101.9
127.3
–
–
–
–
–
It was also reported that, whereas a diode laser had
no influence on Ti disks, Nd:YAG, holmium-doped YAG,
and Er:YAG lasers affected Ti disks, depending on the
type of surface and the power setting of the laser.15 On
the other hand, it was reported that no change was observed on the surface of a Ti plasma spray–coated implant that had been irradiated with an Er,Cr:YSGG laser
at 6 W.16
Several implant surface treatments, including anodization, hydroxyapatite coating, sandblasting, and
Ti plasma spray coating, are currently being used to
enhance implant osseointegration, and several reports have shown good osseointegration with anodized surfaces.17–21 Several studies have examined the
effect of a laser on the surfaces of titanium disks and
implants14,16,22,23; however, these were limited to scanning electron microscopic (SEM) analysis. Research is
lacking on whether lasers evoke any changes on the
surface of anodized Ti implants, and if so, what the
various effects are. Therefore, the present study analyzed the morphology, composition, crystal structure,
and surface roughness (Ra) changes of machined
and anodized Ti surfaces following irradiation with
Er,Cr:YSGG, Er:YAG, and CO2 lasers.
Materials and Methods
Titanium Disk Preparation and Anodic Oxidation
A total of 72 Ti disks (25 mm in diameter, 1 mm in
thickness) were fabricated using commercially pure
Ti (Warantec Co). Prior to use, degreasing and acid
prepickling of all disks were done by washing in acetone, processing through 2% ammonium fluoride/2%
hydrofluoric acid/10% nitric acid solution at 55°C for
30 seconds, and pickling in 2% hydrofluoric acid/10%
nitric acid at room temperature for 30 seconds. Thirtysix of the pretreated disks were then further processed
to produce an anodized surface. Anodic oxidation of
these disks was performed at 300 V in an aqueous electrolytic solution of 0.02 mol/L calcium glycerophosphate (CaC3H7O6P) and 0.15 mol/L calcium acetate. All
procedures were done at room temperature, and the
total time required to anodize each disk was 3 minutes.19–21 All disks were washed with distilled water,
dried, and then sterilized in ethylene oxide gas before
the experiments.
Laser Equipment and Irradiation Methods
The following laser devices and parameters were used
in this study.
1. Er,Cr:YSGG laser (λ = 2,780 nm) (Waterlase MD,
Biolase Technology). Disks were irradiated at five
different powers (1, 2, 3, 4, and 5 W) with an adjustable air-water spray and a pulse frequency fixed at
20 pulses per second according to the manufacturer’s instructions. The delivery system consisted
of a fiber-optic tube terminating in a zirconia tip
(600 µm diameter).
2. Er:YAG laser (λ = 2,940 nm) (KaVo Key-Laser 3,
KaVo). The disks were irradiated at five different
powers (1, 2, 3, 4, and 5 W) with an adjustable airwater spray and a pulse frequency fixed at 20 pulses per second. The laser light was delivered by an
optic fiber and a 500-µm zirconia application tip.
3. CO2 laser (λ = 10,600 nm) (Panalas CO5Σ, Panasonic). The disks were irradiated at five different powers (1, 2, 3, 4, and 5 W) in the pulsing mode at 20
pulses per second. The tip diameter was 500 µm.
The distance from the end of each laser tip to the
surface of the titanium substrate was kept constant at
1.5 mm by using a clamp. The disks were irradiated for 30
seconds, and the angle of irradiation was 90 degrees for
all lasers. Other laser parameters are recorded in Table 1.
Surface Analyses
First, the disks were examined under SEM to determine the surface characteristics. All samples were introduced into the vacuum chamber of a field-emission
SEM (S-4700, Hitachi) and observed at ×100, ×500,
and ×1,000 magnifications.
Next, electron probe microanalysis (EPMA) (JXA8900R, JEOL) was performed to assess alterations in the
surface composition of the disks after laser irradiation.
Element detection and visual analysis of laser-irradiated
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Park et al
Fig 1 SEM images of the machined Ti
surface after Er,Cr:YSGG laser irradiation.
Top row, left to right: 1 W, 2 W, 3 W; bottom
row, left to right: 4 W, 5 W (magnification
×500). After lasing at 3 W, the machined
surface showed melting, coagulation, and
microfractures.
areas were done simultaneously by verification of electron beam–induced x-ray radiation.
Third, x-ray diffractometry (XRD) (D8 ADVANCE,
Bruker AXS) was employed to evaluate changes in the
crystal structure after laser irradiation. Cu-Kα radiation (λ = 1.54050 Å) generated at 40 kV and 20 mA was
used. Disk specimens were fixed parallel to the plane
of the holder. Data were collected at 2θ, between 25
and 75 degrees, with a step size of 0.02 degree and a
normalized counting time of 2 s/step.
Finally, optical interferometry (Accura 2000, Intek
Plus) was used to determine surface roughness. Ten
disks from each group were subjected to surface analysis. Three different 250-× 80-µm areas of each disk
were measured. One-way analysis of variance was conducted to evaluate the effect of the power setting on
surface roughness. The Tukey post hoc test was used
for multiple comparisons, and the significance level
was set at 5%.
Results
Surface Morphology
The Er,Cr:YSGG laser at 1 or 2 W of power did not alter
the disk surface, regardless of the surface type. After
lasing at 3 W, the machined Ti surface exhibited melting, coagulation, and microfractures. The scale of the
damage was proportional to the power output (Fig 1).
On the anodized Ti surface, exfoliation of the coated
surface was observed at 3 W, and melting, coagulation,
and microfracture were observed at 4 and 5 W (Fig 2).
Use of the Er:YAG laser at 1 W did not alter the disk
surface. After lasing at 2 W, microscopic surface changes
were observed on both kinds of Ti surfaces. At 2 and 3 W,
the machined Ti surface displayed mild microscopic
changes, and the anodized Ti surface exhibited exfoliation of the coated surface. At 4 and 5 W, melting, coagulation, and microfractures were observed on both the
machined and the anodized Ti surfaces (Figs 3 and 4).
No alteration of the Ti surface was detected after
CO2 laser irradiation, regardless of the surface treatment (machined or anodized) or power applied.
Surface Composition
Nonirradiated Surface. Ti, O, N, and C were detected
on the machined Ti surface (Table 2). An exact proportion of N could not be measured because of the similarity of the N signal to the Ti signal. By percentage of
weight, the majority of the surface was composed of
Ti (91.188%), and small amounts of O (2.537%) and
C (0.295%) were detected as well. On the anodized
Ti surface, Ti, O, N, C, Ca, and P were detected (Table
2), indicating that the Ca (9.724%) and P (4.936%)
were generated by the anodic oxidation process. Ti
(48.568%) was detected in the highest proportion, but
a high proportion of O (30.818%) was present as well
following the anodic oxidation process.
Er,Cr:YSGG Laser. When the machined Ti surface was
irradiated with a power of at least 3 W, the proportion
of O increased and the proportion of Ti decreased in
comparison with the nonirradiated disk (Table 3). When
the anodized Ti surface was lased at 3 W, the proportion
of Ti was unchanged, but when the surface was lased at
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Fig 2 SEM images of the anodized Ti surface after Er,Cr:YSGG laser irradiation. Top
row, left to right: 1 W, 2 W, 3 W; bottom
row, left to right: 4 W, 5 W (magnification
×500). Exfoliation of the coated surface
was observed at 3 W; melting, coagulation, and microfractures were observed at
4 W and 5 W.
Fig 3 SEM images of the machined Ti
surface after Er:YAG laser irradiation. Top
row, left to right: 1 W, 2 W, 3 W; bottom
row, left to right: 4 W, 5 W (magnification ×500). At 2 W and 3 W, the surface
showed mild microscopic changes. Melting, coagulation, and microfractures were
observed at 4 W and 5 W.
4 or 5 W, the proportion of O increased. The proportions
of N and C were not affected by the laser treatment.
Er:YAG Laser. When the machined Ti surface was
irradiated with a power above 2 W, the proportion of
O increased and the proportion of Ti decreased versus
the nonirradiated disk (Table 4). When the anodized
Ti surface was irradiated with a power above 2 W, the
proportion of O decreased and the proportion of Ti increased in comparison to the nonirradiated disk. When
the disk was lased at 2 W, C and P were detected. When
the disk was lased at 3 W, only a very small amount of
Ca was detected.
Crystal Structure
Irradiation with the Er,Cr:YSGG laser did not change the
crystal structure of the machined Ti surface, even at 5
W. Only Ti peaks were observed both before and after
laser irradiation (Fig 5). On the other hand, the XRD
pattern of the anodized Ti surface exhibited a change
in the crystal structure after lasing. As the power of
the Er,Cr:YSGG laser was increased from 3 to 5 W, the
anatase peak intensity diminished and the rutile peak
intensity increased (Fig 6).
When the machined Ti surface was irradiated with
the Er:YAG laser at more than 3 W, weak anatase and
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Fig 4 SEM images of the anodized Ti surface after Er:YAG laser irradiation. Top row,
left to right: 1 W, 2 W, 3 W; bottom row, left
to right: 4 W, 5 W (magnification ×500). At
2 W and 3 W, the coated surface exhibited
exfoliation. Melting, coagulation, and micro
fractures were observed at 4 and 5 W.
Table 2 Composition of the Disks Prior to Irradiation
Composition (% by weight)
Surface
Machined
Anodized
O
N
C
Ti
Ca
P
2.537
5.979
0.295
91.188
–
–
30.818
4.704
1.008
48.568
9.724
4.936
Table 3 Composition of the Disks After Er,Cr:YSGG Laser Irradiation
Surface/
laser power
Composition (% by weight)
O
N
C
Ti
Ca
P
Machined
3 W
4 W
5 W
58.667
57.67
62.478
9.976
10.805
10.1
1.382
0.745
0.791
29.975
30.781
26.631
–
–
–
–
–
–
Anodized
3W
4W
5W
30.563
47.846
44.678
6.501
3.808
4.788
4.656
1.849
1.623
58.281
46.498
48.911
–
–
–
–
–
–
Table 4 Composition of the Disks After Er:YAG Laser Irradiation
Surface/laser
power
Composition (% by weight)
O
N
C
Ti
Ca
P
Machined
2 W
3 W
4 W
5 W
5.77
12.263
24.189
34.978
8.676
8.964
5.418
5.594
0.912
1.365
0.272
0.314
84.642
77.408
70.121
59.114
–
–
–
–
–
–
Anodized
2 W
3 W
4 W
5 W
31.493
23.405
17.717
15.249
1.783
2.349
4.194
0.948
0.549
0.383
0.653
4.387
59.273
73.838
77.329
79.371
4.864
0.025
0.058
0.04
2.038
–
0.05
0.006
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Table 5 Surface Roughness (Ra) of the Ti Surface After Laser Irradiation
Ra (mean ± SD) (μm)
Laser type/power
Machined surface
Anodized surface
0.112a
0.873 ±
P value*
0.162a
None
0.541 ±
Er,Cr:YSGG
3 W
4 W
5 W
1.370 ± 0.400b
1.370 ± 0.400b
1.572 ± 0.196b
1.272 ± 0.224b
1.375 ± 0.274b
1.359 ± 0.361b
Er:YAG
2 W
3 W
4 W
5 W
0.940 ± 0.235b
1.470 ± 0.290b
1.436 ± 0.468b
1.589 ± 0.326b
0.931 ± 0.122a
1.209 ± 0.155b
1.341 ± 0.121b
1.304 ± 0.259b
< .05
< .05
*Versus nonirradiated disks (one-way analysis of variance). a,bValues with the same letter are not significantly different (Tukey post hoc test; P > .05).
Titanium
Antase
Rutile
Titanium
Antase
Rutile
5W
4W
3W
Intensity
Intensity
5W
4W
3W
Control
20
30
40
50
2θ/deg
60
70
80
Fig 5 XRD patterns of the machined Ti surface after Er,Cr:YSGG
laser irradiation. Only typical Ti peaks were observed before and
after laser irradiation.
Titanium
Antase
Control
20
30
40
50
60
2θ/deg
70
Fig 6 XRD patterns of the anodized Ti surface after Er,Cr:YSGG
laser irradiation. After laser irradiation, rutile peaks appeared,
and as the laser power was increased from 3 W to 5 W, the
anatase peak intensity decreased and the rutile peak intensity
increased.
Titanium
Rutile
Antase
Rutile
20
30
40
50
2θ/deg
60
70
5W
Intensity
Intensity
5W
4W
80
4W
3W
3W
Control
Control
80
20
30
40
50
2θ/deg
60
70
80
Fig 7 XRD patterns of the machined Ti surface after Er:YAG
laser irradiation. Irradiation with a power over 3 W caused not
only typical Ti peaks but also weak anatase and rutile peaks.
Fig 8 XRD patterns of the anodized Ti surface after Er:YAG
laser irradiation. With increased laser power, rutile peaks appeared and the intensity of the anatase peaks decreased.
rutile peaks were observed, in addition to the Ti peaks.
The peak intensity was not proportional to the increase
in laser power (Fig 7). When the anodized Ti surface
was irradiated with a power over 3 W, more anatase
and rutile peaks appeared. With increased laser power,
the intensity of the anatase peaks diminished (Fig 8).
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Surface Roughness
The mean Ra values before and after laser irradiation
at various power settings and on the different Ti surfaces are shown in Table 4. After irradiation with the
Er,Cr:YSGG laser at a power setting above 3 W, the Ra
values of the machined and anodized Ti surfaces increased significantly, as compared to the nonirradiated surfaces (P < .05). After Er:YAG laser irradiation,
the Ra values of the machined Ti disk increased significantly when a power setting over 2 W was used, but on
the anodized Ti surface, 3 W of power were required to
achieve the same result (P < .05).
Discussion
Lasers have been used with increasing frequency for
the treatment of oral injuries, in maxillofacial soft and
hard tissue surgery, and for implant dentistry.3,5 Studies have proven the effectiveness of laser irradiation
for soft tissue wound healing, osteoblast proliferation,
and bone healing.24–26 Because of these benefits, lasers
have been used in dentistry for implant placement,
stage-two surgery, soft tissue management, and periimplantitis treatment.1,2,27 In peri-implantitis treatment,
the implant surface is directly exposed to the laser. Because of the widespread use of lasers for dental applications, it is of great importance to understand the impact
of the laser on the titanium surface of an implant. However, research is lacking on whether the laser causes any
changes on the various surfaces of titanium implants.
Moreover, past research has yielded a variety of differing
results with the use of different laser types, manufacturers, and irradiation modes14,15,22; in addition, studies to
date have been limited to SEM analysis. In the present
study, the morphology, composition, crystal structure,
and Ra changes of machined and anodized Ti surfaces
after irradiation were analyzed.
According to the results of the present study, the
Ti disk surfaces were affected by irradiation with the
Er,Cr:YSGG laser at powers over 3 W and the Er:YAG
laser at powers over 2 W. The disk was copiously airwater–sprayed, but there seemed to be a limit to the
effectiveness of this. The CO2 laser did not cause any
surface alterations. One of the most important properties of the laser is its wavelength. The wavelength of
the Er,Cr:YSGG laser is 2,780 nm; for the Er:YAG laser, it
is 2,940 nm. The wavelength of the CO2 laser is 10,600
nm, which is the longest of those compared. Therefore,
the reflection rate of the CO2 laser against a Ti surface
is high and the energy delivery is low, which makes it
possible for the Ti disk to avoid surface changes despite
a high power setting.7,28–30 Changes such as melting,
coagulation, or exfoliation of the coated surface of implants after laser irradiation may have a negative effect
on bone-to-implant contact and affect the success of
implant treatment. Based on the results of this study, if
a laser must be directly irradiated on the implant surface, it can be said that, if possible, use the Er,Cr:YSGG
laser at a power below 3 W, the Er:YAG laser below 2 W,
and the CO2 laser at a power as high as 5 W.
On the nonirradiated machined Ti surface, Ti, O, N,
and C were detected. In the present study, the Ti disks
were made of commercially pure Ti. However, Ti quickly absorbs and reacts with elements in air, such as C, O,
and N.12 Oxygen binds to the Ti surface, creating a thin,
amorphous oxide (TiO2) layer. Anodization increases
the amount of O, resulting in a TiO2 layer that consists
of primarily the anatase phase.19,20,31 When the surface
composition was analyzed after laser irradiation of the
machined Ti surface, it was possible to observe that
the proportion of O was increased. It appears that the
alteration of Ti surfaces by laser irradiation is caused by
oxidation. In the present study, the proportion of O on
the anodized surface did not increase with increases in
the power of the laser, because removal of the oxidized
layer and surface oxidation took place concurrently.
After laser irradiation, the crystal structure of the
anodized surface was noticeably altered. Increases
in the laser power delivered to the surface decreased
the anatase peak and increased the rutile peak. With
respect to the heat treatment and the XRD pattern of
the TiO2 coating, the coating had Ti reflections up to
300°C, but above that, anatase reflections and rutile reflections were observed.32 Since anatase crystals made
up the majority of the anodized Ti surface in the present study, it appeared that laser irradiation removed
anatase crystals and replaced them with rutile crystals.
This work indicated that laser irradiation significantly increased the Ra value of the Ti surfaces. Osseointegration of Ti implants is achieved by direct
bone-to-implant contact on the microscopic level.33
The surface quality of the implant depends on the
chemical, physical, mechanical, and topographic properties of the surface, properties that, in turn, affect the
response of osteoblasts to the Ti surface.19–21,34,35 The
physical and/or chemical variations, including threedimensional changes in surface topography, caused by
laser treatment of the Ti substrate may play an important role in the initial biocompatibility of the implant.24
During irradiation, parameters such as wavelength,
output power, energy, dose, and duration should be
considered. A previous study indicated that irradiation
of anodized Ti disks with a CO2 or Er,Cr:YSGG laser had
a positive effect on osteoblast proliferation and differentiation.13 In that study, power outputs of 1.5, 2, and
2.5 W were selected, and the energy (dose) was set to
provide a sufficient laser dosage to the surface. The use
of a high-power laser at a low power allows an adequate dose to be delivered to the Ti surface, preventing
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undesirable results and positively influencing the attachment and spread of osteoblasts. Furthermore, to
achieve more predictable results, it is important to
move the laser continuously, not staying too long in
one spot, and to avoid bringing the laser tip too close
to the metal. In summary, the present study indicated
that the power output of the laser should be controlled
to avoid undesirable implant surface changes and to
ensure that the effects of the laser are positive.
Conclusions
After irradiation with erbium-doped ytrrium-aluminumgarnet and erbium chromium–doped yttrium-scandiumgallium-garnet lasers, surface changes occurred on
titanium disks depending on the power output. The
carbon dioxide laser did not cause any surface changes,
regardless of the power output, in this experimental
model. Laser power output should be limited to avoid
surface damage, and controlled application is necessary
as appropriate for the laser type.
Acknowledgment
This work was supported by grant no. 03-2010-0022 from the
SNUDH Research Fund.
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