effects of laser irradiation on machined and anodized...

The International Journal of Oral & Maxillofacial Implants 265

Lasers have been used frequently in the field of dentist-ry. Because of various advantages in ablation, decon-

tamination, and hemostasis, laser treatment has been

expected to serve as an alternative or adjunct to con-ventional 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-gal-lium-garnet (Er,Cr:YSGG) and erbium-doped yttrium-aluminum-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 peri- implantitis.1,2 Lasers have been used to modify the sur-face of dental implants or to decontaminate exposed implant surfaces.7,10–12 A previous study showed that ir-radiation of titanium (Ti) disks with a CO2 or Er,Cr:YSGG laser could induce osteoblast proliferation and differ-entiation.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 la-ser 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.

1 Clinical Lecturer, Department of Prosthodontics and Dental Research Institute, School of Dentistry, Seoul National University, Seoul, South Korea.

2 Professor, Department of Prosthodontics and Dental Research Institute, School of Dentistry, Seoul National University, Seoul, South Korea.

3 Associate Professor, Department of Prosthodontics and Dental Research Institute, Seoul National University Dental Hospital, School of Dentistry, Seoul National University, Seoul, South Korea.

4 Professor, Department of Prosthodontics, Yongdong Severance Dental Hospital, College of Dentistry, Yonsei University, Seoul, South Korea.

5 Assistant 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]

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-gallium-

garnet (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

© 2012 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

Park et al

266 Volume 27, Number 2, 2012

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 ob-served on the surface of a Ti plasma spray–coated im-plant that had been irradiated with an Er,Cr:YSGG laser at 6 W.16

Several implant surface treatments, including an-odization, hydroxyapatite coating, sandblasting, and Ti plasma spray coating, are currently being used to enhance implant osseointegration, and several re-ports have shown good osseointegration with anod-ized 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 scan-ning 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 ana-lyzed 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 oxidationA 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 ace-tone, 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. Thirty-six 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 elec-trolytic solution of 0.02 mol/L calcium glycerophos-phate (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 min-utes.19–21 All disks were washed with distilled water, dried, and then sterilized in ethylene oxide gas before the experiments.

laser equipment and irradiation MethodsThe 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 adjust-able air-water spray and a pulse frequency fixed at 20 pulses per second according to the manufac-turer’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 air-water spray and a pulse frequency fixed at 20 puls-es 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, Panason-ic). The disks were irradiated at five different pow-ers (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 analysesFirst, the disks were examined under SEM to deter-mine the surface characteristics. All samples were in-troduced 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) (JXA-8900R, JEOL) was performed to assess alterations in the surface composition of the disks after laser irradiation. Element detection and visual analysis of laser-irradiated

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

50100150200250

17.735.453.170.788.4

1015202530

Er:YAG 1 W 2 W 3 W 4 W 5 W

50100150200250

25.550.976.4

101.9127.3

1015202530

CO2

1 W 2 W 3 W 4 W 5 W

50100150200250

25.5 50.9 76.4

101.9 127.3

–––––


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areas were done simultaneously by verification of elec-tron 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 radia-tion (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 anal-ysis. Three different 250-× 80-µm areas of each disk were measured. One-way analysis of variance was con-ducted 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 MorphologyThe 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 melt-ing, 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 exfolia-tion of the coated surface. At 4 and 5 W, melting, coagu-lation, 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 treat-ment (machined or anodized) or power applied.

surface CompositionNonirradiated Surface. Ti, O, N, and C were detected on the machined Ti surface (Table 2). An exact propor-tion of N could not be measured because of the simi-larity 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

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.


Park et al


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 in-creased 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 structureIrradiation 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

Fig 2 SEM images of the anodized Ti sur-face 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, coagula-tion, 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 (magnifica-tion ×500). At 2 W and 3 W, the surface showed mild microscopic changes. Melt-ing, coagulation, and microfractures were observed at 4 W and 5 W.


Park et al


Fig 4 SEM images of the anodized Ti sur-face 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

surface

Composition (% by weight)

o n C ti Ca P

Machined 2.537 5.979 0.295 91.188 – –

Anodized 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


o n C ti Ca P

Machined 3 W 4 W 5 W

58.66757.6762.478

9.97610.80510.1

1.3820.7450.791

29.97530.78126.631

–––

–––

Anodized 3W 4W 5W

30.56347.84644.678

6.5013.8084.788

4.6561.8491.623

58.28146.49848.911

–––

–––

table 4 Composition of the disks after er:YaG laser irradiation

surface/laser power


o n C ti Ca P

Machined 2 W 3 W 4 W 5 W

5.7712.26324.18934.978

8.6768.9645.4185.594

0.9121.3650.2720.314

84.64277.40870.12159.114

–––

–––

Anodized 2 W 3 W 4 W 5 W

31.49323.40517.71715.249

1.7832.3494.1940.948

0.5490.3830.6534.387

59.27373.83877.32979.371

4.8640.0250.0580.04

2.038–

0.050.006


Park et al


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).

table 5 surface roughness (ra) of the ti surface after laser irradiation

laser type/power

ra (mean ± sd) (μm)

P value*Machined surface anodized surface

None 0.541 ± 0.112a 0.873 ± 0.162a < .05

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

*Versus nonirradiated disks (one-way analysis of variance). a,bValues with the same letter are not significantly different (Tukey post hoc test; P > .05).

Inte

nsity

20 30 40 50

5 W

Titanium

4 W

3 W

Control

2θ/deg

60 70 80

Antase Rutile

Inte

nsity

20 30 40 50

5 W

Titanium

4 W

3 W

Control

2θ/deg

60 70 80

Antase Rutile

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.

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.

Inte

nsity

20 30 40 50

5 W

Titanium

4 W

3 W

Control

2θ/deg

60 70 80

Antase Rutile

Inte

nsity

20 30 40 50

5 W

Titanium

4 W

3 W

Control

2θ/deg

60 70 80

Antase Rutile

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 ap-peared and the intensity of the anatase peaks decreased.


Park et al


surface roughnessThe mean Ra values before and after laser irradiation at various power settings and on the different Ti sur-faces 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 in-creased significantly, as compared to the nonirradi-ated surfaces (P < .05). After Er:YAG laser irradiation, the Ra values of the machined Ti disk increased signifi-cantly 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 Stud-ies 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 peri-implantitis treatment.1,2,27 In peri-implantitis treatment, the implant surface is directly exposed to the laser. Be-cause of the widespread use of lasers for dental applica-tions, it is of great importance to understand the impact of the laser on the titanium surface of an implant. How-ever, 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, manufactur-ers, 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 air-water–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 proper-ties 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 im-plants 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 sur-face, 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 quick-ly 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 re-flections were observed.32 Since anatase crystals made up the majority of the anodized Ti surface in the pres-ent study, it appeared that laser irradiation removed anatase crystals and replaced them with rutile crystals.

This work indicated that laser irradiation signifi-cantly increased the Ra value of the Ti surfaces. Os-seointegration 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 prop-erties 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 three-dimensional changes in surface topography, caused by laser treatment of the Ti substrate may play an impor-tant 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 differ-entiation.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 ade-quate dose to be delivered to the Ti surface, preventing


Park et al


undesirable results and positively influencing the at-tachment 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-aluminum- garnet and erbium chromium–doped yttrium-scandium- gallium-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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