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Objective: The aim of this review was to evaluate the balling phenomenon which occurs typically in Selective Laser Sintering (SLS)., Background Data: The balling phenomenon is a typical SLS defect, and observed in laser sintered powder, significantly reduces the quality of SLS, and hinders the further development of SLS Technology., Methods: Electronic database searches were performed using Google Scholar. The keywords "laser sintering, selective laser sintering, direct metal laser melting, and balling phenomenon" were searched in title/abstract of publications, limited to December 31, 2016. The inclusion criteria were SLS, balling phenomenon, some alloys (such as Cr-Co, iron, stainless steel, and Cu-based alloys) mechanical properties, microstructure and bond strength between metal-ceramic crown, laboratory studies, full text, and in English language., Results: A total of 100 articles were found the initial search and yielded a total of 50 studies, 30 of which did not fulfill the inclusion criteria and were therefore excluded. In addition, 20 studies were found by screening the reference list of all included publications. Finally, 40 studies were selected for this review., Conclusions: The method in question is regulated by powder material characteristics and the conditions of laser processing. The procedure of formation, affecting factors, and the mechanism of the balling effect are very complex.

Objective: Laser modalities and direct metal laser sintering (DMLS) have a potential to enhance micromechanical bonding between dental super- and infrastructures. However, the effect of different manufacturing methods on the metal-ceramic bond strength needs further evaluation. We investigated the effect of surface treatment with Er:YAG, Nd:YAG, and Ho:YAG lasers on the shear bond strength (SBS) of high-fusion dental porcelains (Vita and G-Ceram) to infrastructures prepared with DMLS in vitro settings., Materials and Methods: Study specimens (n = 128) were randomly divided into study subsets (n = 8), considering treatment types applied on the surface of infrastructures, including sandblasting and selected laser modalities; infrastructure types as direct laser sintered (DLS) and Ni-Cr based; and superstructure porcelains as Vita and G-Ceram. The SBS test was performed to assess the effectiveness of surface modifications that were also examined with a stereo microscope., Results: Considering laser procedure types, the highest SBS values were obtained by Er:YAG laser, followed by, with a decreasing efficiency, Ho:YAG laser and sandblasting procedures, and Nd:YAG laser procedure (p < 0.05). Nd:YAG laser decreases the bonding of Vita and G-Ceram in all the infrastructures compared with sandblasting. Considering porcelains, the highest SBS values were obtained by Vita (p < 0.05). Considering infrastructures, the highest SBS values were obtained by DMLS procedure (p < 0.05). The laser procedures caused surface irregularities as revealed by the stereo microscopic examination., Conclusions: In current experimental settings, Er:YAG laser applied to DLS infrastructure veneered with Vita porcelain increases bonding strength more distinctly, and Nd:YAG laser applied to Ni-Cr-based infrastructure veneered with G-Ceram porcelain alters bonding strength unfavorably.

Objective: Laser irradiation is an alternative surface treatment method for roughening zirconia surfaces. The aim of this study was to evaluate the effects of ytterbium-doped fiber laser (YbPL) on zirconia., Background: Zirconia surfaces are resistant to many surface treatment methods, but surface roughness is crucial for adhesion of veneering materials and cements to zirconia., Methods: The zirconia discs were prepared and divided into four groups according to the power of the laser irradiation (5, 12, 17, and 20 W). These groups were divided into five subgroups according to the frequency (25, 40, 60, 80, and 100 kHz). Surface roughness values were measured with a noncontact profilometer, and the mean Ra values were calculated. Wettability was measured with a goniometer. The surface morphology was observed with a scanning electron microscope (SEM). The changes in the surface crystalline structure were analyzed with X-ray diffractometry., Results: Ra values of all groups were higher than the control group. The highest surface roughness value was at 20 W and 100 kHz. Best wettability characteristic was observed at 5 W and 60 kHz. The correlations between Ra and wettability were low but significant. SEM examination of 5 W with different frequencies showed no microcracks, however, melted areas were observed. Remaining groups had microcracks and melted layers. A significantly lower T/M-phase transformation was observed in some groups., Conclusions: YbPL irradiation was effective at roughening the zirconia surface. Although laser treatment affected zirconia surfaces and provided surface roughness, the power and frequency should be adjusted to achieve optimum results.

Objective: The purpose of this study was to evaluate the effect of surface and heat treatments on the mechanical properties and phase transformation of yttria-stabilized tetragonal zirconia (Y-TZP) materials., Background Data: Zirconia is exposed to several treatments during dental application process. Knowing the effect of applied treatments on zirconia is essential for clinical success., Material and Methods: Forty disk specimens of Zirkonzahn (Z) and DC-Zirkon (DC) materials were fabricated. The specimens were randomly divided into four groups according to surface [control, sandblasting, Erbium: Yttrium Aluminum Garnet (Er:YAG) laser irradiation] and heat (firing) treatments. The surface roughness (Ra, μm) was measured using a surface profilometer. The relative amount of the transformed monoclinic (m) phase was analyzed by X-ray diffractometry (XRD). Biaxial flexural strength was tested using piston-on-three-ball technique. The data were analyzed with the Kruskal-Wallis H test with Bonferroni correction, and the Mann-Whitney U test was used for pairwise comparisons., Results: There were no significant differences in surface roughness among the treated groups (p > 0.05), whereas sandblasting showed higher surface roughness than other treatments for both materials. Scanning electron microscopic (SEM) analyses revealed changes in surface morphology after surface treatments, especially in laser groups with the formation of cracks, and in sandblasting groups with the formation of microretentive grooves. The greatest amount of the monoclinic phase was measured after sandblasting (8.13%) for Z and (19.8%) for DC. The monoclinic phase reverted to the tetragonal phase after heat treatment. Heat treatment groups showed significantly lower flexural strength than other treatments (p < 0.05)., Conclusions: Heat and surface treatments influenced the mechanical properties of zirconia ceramic. The biaxial flexural strength and crystalline phase of materials decreased after heat treatments.

Objective: The purpose of this study was to evaluate surface roughness and changes in the composition of enamel submitted to different bleaching protocols and toothbrushing with regular and whitening toothpastes., Background Data: Bleaching treatment could promote morphological and chemical changes in enamel surface., Methods: Enamel blocks were randomized into nine groups (n=10) according to the bleaching treatment (no bleaching, control group; 6% hydrogen peroxide, HP; or 10% carbamide peroxide, CP) and toothpaste used (placebo, PL; regular, R; or whitening dentifrice, W). Bleaching was performed according to manufacturers' instructions and all groups were submitted to 30,000 cycles of simulated toothbrushing with toothpaste (PL, R, or W). Mineral content evaluation and enamel roughness were evaluated initially (T1), after bleaching (T2), and after toothbrushing (T3), using an energy-dispersive micro X-ray fluorescence spectrometer and profilometry, respectively. Data were statistically analyzed with two way ANOVA, Tukey, and Dunnett tests (5%)., Results: Enamel surface roughness was influenced by bleaching and toothbrushing. Surface roughness increased for the groups that brushed with the placebo dentifrice (CP+PL, HP+PL, C+PL) and for the control group that brushed with whitening dentifrice (C+W). Enamel Ca/P ratio decreased after bleaching, but toothbrushing, regardless of the dentifrice used, did not reduce the enamel mineral content., Conclusions: The bleaching treatment resulted in a decrease of enamel mineral content, but the studied dentifrices did not contribute to surface mineral loss.

Objective: This in vitro study evaluated the effect of different bleaching protocols and the variation of pH levels of bleaching gels regarding roughness and wear of bovine enamel, after in-office bleaching protocols and brushing., Materials and Methods: Ninety fragments were randomly divided into nine groups: C, control; WHP15, 35% hydrogen peroxide (HP) (Whiteness HP, FGM) three gel applications of 15 min each, three sessions with 1 week intervals; WHP45, 35% HP (Whiteness HP) one application/45 min, three sessions with 1 week intervals; LPS, 35% HP (Lase Peroxide, DMC) plus hybrid light (HL) [light-emitting diode (LED)/diode laser], four applications/7 min 30 sec (6 min of HL activation), one session; LPSII, 25% HP (Lase Peroxide II, DMC) plus HL, four applications/7 min 30 sec (6 min of HL activation), one session; LPL, 15% HP (Lase Peroxide Light, DMC) four applications/7 min 30 sec (6 min of HL activation), one session; WO, 35% HP (Whitegold Office, Dentsply) three applications/15 min, three sessions with 1 week intervals; WBC40, 35% HP (Whiteness HP Blue Calcium, FGM) one application/40 min, three sessions with 1 week intervals; and WBC50, 20% HP (Whiteness HP Blue Calcium) one application/50 min, three sessions with 1 week intervals. The median pH values were determined utilizing a pH meter during the initial and final gel applications. A rugosimeter was utilized to evaluate the surface roughness (Ra) before and after bleaching and brushing (100,000 strokes), and the surface wear after brushing., Results: For the results of the pH values, there was a decrease in the pH levels from the initial to the final bleaching time, except for the WBC50. The WO and WBC40 groups exhibited higher pH values. For the results of roughness and wear, there was an increase in surface roughness and wear among the groups., Conclusions: The pH values tended to decrease from the initial to the final bleaching. After tooth brushing, bleaching procedures with lower pH products provided a significant increase in enamel wear and surface roughness.

Objective: The aim of this study was to test whether Er:YAG laser-etched enamel of human teeth could act as a biologically active scaffold for tissue regeneration., Background Data: Hydroxylapatite (HA) with rough surface created by acid etching treatment has been used as a scaffold for tissue engineering. However, whether tooth HA can be a scaffold for osteoblastic cell seeding is still unclear., Materials and Methods: Enamel samples from human teeth were pretreated with an Er:YAG laser to create a rough surface. Then the surface of the laser-treated enamel was examined using a surface roughness profilometer and a scanning electron microscope. In addition, static water contact angles of the Er:YAG laser-treated enamel samples were measured using goniometry. To observe the effects of cell behavior on an Er:YAG laser-roughened enamel surface, we cultured MG63 osteoblast-like cells on the surface-modified enamel samples. Alkaline phosphatase activity, a marker of cell proliferation and differentiation, was monitored and compared with that in untreated control and acid-etched enamel samples., Results: Er:YAG laser treatment significantly improved the surface roughness of the enamel samples. Furthermore, MG63 osteoblast-like cells cultured on the Er:YAG laser-roughened enamel surface expressed more alkaline phosphatase activity and exhibited greater degrees of cellular differentiation than did cells that had been cultured on untreated enamel samples., Conclusions: These results demonstrate that Er:YAG laser-roughened enamel promotes osteoblastic differentiation. This finding suggests that Er:YAG laser-roughened enamel surfaces can potentially serve as a scaffold for tissue engineering.

Objective: The aim of this study was to evaluate the roughness and morphology of zirconia after air abrasion and erbium:yttrium-aluminum-garnet (Er:YAG) laser application of different intensities., Background Data: Although surface roughness is important to obtain micromechanical retention, it is unclear which surface treatment is most appropriate for zirconia., Methods: Fifty sintered zirconia specimens were divided into five groups (n=10). The following treatments were applied: control, Er:YAG laser irradiation with different energy intensities (200, 300, and 400 mJ), and air abrasion with aluminum oxide (Al(2)O(3)) particles (110 μm). Morphologic changes after surface treatments were examined in microscope analyses. Then, the surface roughness (Ra in μm) of the specimens was evaluated using a surface texture measuring instrument. Roughness data were analyzed using one-way analysis of variance (ANOVA) and Tukey's honestly significant difference (HSD) test (p=0.05)., Results: Results of microscope analyses revealed changes in surface morphology after surface treatments, including the formation of rare pits in the 400 mJ laser group and the formation of microretentive grooves in the air abrasion group. According to the results of the statistical analysis, the mean surface roughness value for the air abrasion group was significantly higher than that of the other groups (p<0.001). Except for the air abrasion group, there were no statistically significant differences within other groups (p>0.05)., Conclusions: According to the results of the statistical and microscopic analyses, 400 mJ Er:YAG laser energy or air abrasion can be used to obtain micromechanical retention prior to luting; however, air abrasion is the most effective surface treatment method.

Objective: The aim of this study was to assess by atomic force microscopy (AFM) the effect of Er,Cr:YSGG laser application on the surface microtopography of radicular dentin., Background: Lasers have been used for various purposes in dentistry, where they are clinically effective when used in an appropriate manner. The Er,Cr:YSGG laser can be used for caries prevention when settings are below the ablation threshold., Materials and Methods: Four specimens of bovine dentin were irradiated using an Er,Cr:YSGG laser (λ = 2.78 μm), at a repetition rate of 20 Hz, with a 750-μm-diameter sapphire tip and energy density of 2.8 J/cm(2) (12.5 mJ/pulse). After irradiation, surface topography was analyzed by AFM using a Si probe in tapping mode. Quantitative and qualitative information concerning the arithmetic average roughness (Ra) and power spectral density analyses were obtained from central, intermediate, and peripheral areas of laser pulses and compared with data from nonirradiated samples., Results: Dentin Ra for different areas were as follows: central, 261.26 (±21.65) nm; intermediate, 83.48 (±6.34) nm; peripheral, 45.8 (±13.47) nm; and nonirradiated, 35.18 (±2.9) nm. The central region of laser pulses presented higher ablation of intertubular dentin, with about 340-760 nm height, while intermediate, peripheral, and nonirradiated regions presented no difference in height of peritubular and interperitubular dentin., Conclusion: According to these results, we can assume that even when used at a low-energy density parameter, Er,Cr:YSGG laser can significantly alter the microtopography of radicular dentin, which is an important characteristic to be considered when laser is used for clinical applications.

Objectives: To compare the ability of the Variable Square Pulse technology (VSP-technology)-based erbium-doped yttrium aluminium garnet (Er:YAG) laser working in maximum speed (MAX) mode (1000 mJ, 300 micros, 20 Hz) and the high-speed handpiece to ablate enamel, to compare the ability of for the VSP-technology-based Er:YAG laser working in MAX mode and the low-speed handpiece to ablate dentin, and to analyze in vitro effects of Er:YAG ablation of enamel and dentine surfaces using scanning electron microscopy (SEM)., Background Data: A VSP-technology-based Er:YAG laser operating in MAX mode should be appropriate for achieving the maximum ablating speed in hard dental tissues., Materials and Methods: The experiment was conducted on extracted, cleaned, sterilized human molar teeth. Cavity preparations were made in hard dental tissues using the VSP-technology Er:YAG laser in MAX mode, in enamel using the high-speed handpiece, and in dentin using the low-speed handpiece at different time intervals. A laser triangulation profilometer was used to determine cavity volumes. The cavity surfaces of five specimens were examined using SEM., Results: The Er:YAG laser removed a volume of enamel that was 3.3 times as large as that removed by the high-speed handpiece in the same period of time. In dentin, the Er:YAG laser removed 8 to 18 times as much volume as the steel bur in the same period of time. The Er:YAG ablation rate in dentin was faster than in enamel. SEM of laser prepared cavities showed a well-defined surface, free of the smear layer., Conclusions: The VSP-technology-based Er:YAG laser, working in MAX mode, is more efficient than mechanical drills for enamel and dentin ablation.

Objective: In order to preserve the maximum amount of healthy enamel and increase the acid resistance of decalcified enamel, a CO(2) laser, an Nd:YAG laser, and acidulated phosphate fluoride (APF) were used to treat incipient carious lesions, then their effects were compared., Materials and Methods: One hundred and sixty samples of human caries-free premolars were immersed in pH-cycling solution (pH = 5) for 2 d for decalcified lesion formation. Then the tooth samples were randomly divided into eight groups and the lesions were treated using the different modalities: a control group, an APF only group, an APF = Nd:YAG laser group, and APF = CO(2) laser group, an Nd:YAG laser = APF group, a CO(2) laser = APF group, a CO(2) laser only group, and an Nd:YAG laser only group. The energy density setting for the two types of lasers was 83.33 J/cm(2). After treatment the tooth samples were immersed in pH-cycling solution again for 2 d for acid challenge. As for the acid-resistance evaluation, the calcium concentration dissolved from the enamel surface was analyzed by an electrolyte analyzer. Scanning electron microscopy (SEM) was used to assess morphologic changes and polarized light microscopy (PLM) was used to evaluate optical changes in the lesions., Results: The control group showed a statistically significantly (p < 0.05) higher calcium concentration compared with all the other groups. The APF group also had a statistically significantly higher calcium concentration (p < 0.05) than did the laser groups. However, there was no statistically significant difference in any of the laser groups whether combined with fluoride or not (p > 0.05). Upon SEM analysis, melted surfaces and crater-like holes 1-20 microm in diameter were found in the CO(2) laser and Nd:YAG laser groups. On PLM, positive birefringence and reversal of birefringence after acid challenge of the lased enamel were seen., Conclusions: Using lasers and fluoride on decalcified enamel appears to increase the enamel's acid resistance, and the effects of the lasers were better than those of fluoride treatment.

Objective: The purpose of this study was to evaluate the effect of different surface treatments on bond strength between In-Ceram Zirconia ceramic and Panavia Fluoro Cement., Background Data: Although several surface treatments have been used on In-Ceram Zirconia, no study has been conducted to investigate the effect of the Nd:YAG laser., Materials and Methods: Nine In-Ceram Zirconia blocks (10 x 10 x 6 mm) received three different surface treatments (n = 3 per group): group 1-Al2O3 sandblasting + silane; group 2-Al2O3 sandblasting + Rocatec Plus + silane; and group 3-Al2O3 sandblasting + Nd:YAG laser + silane. Resin cement was applied and light-cured, followed by the application of composite resin. The blocks were sectioned to obtain square rods with a cross-sectional dimension of 1.0 mm2 (n = 12 per group). Microtensile bond strength (muTBS) was recorded using a universal testing machine at a cross-head speed of 0.5 mm/min and expressed in megapascals (MPa)., Results: All groups yielded statistically significantly different muTBS mean values: group 1 (11.81 +/- 3.12 MPa); group 2 (15.75 +/- 4.45 MPa); group 3 (18.70 +/- 5.14 MPa) (ANOVA and Tukey's test; alpha = 0.05)., Conclusion: Nd:YAG laser irradiation is an effective surface treatment for bonding between In-Ceram Zirconia and Panavia Fluoro Cement.

Objective: The objective of this work was to evaluate the importance of the degree of light polarization in stimulation of cellular metabolism., Background Data: Although the possible role of polarization's effects on the mechanisms of laser phototherapy is sometimes discussed in the literature, there are still no clear answers., Material and Methods: A model system (HeLa cell suspension) was used in which the lengths of light scattering (l sc) and absorption (l a) were much larger than the thickness of the irradiated layer (L = 3 mm). The cell suspension (1 x 10(6) cells/cm3) was irradiated with a diode laser (lambda = 637 nm, D = 65.7 J/m2, tau = 10 sec, I = 6.57 W/m2). The polarization degree (99.4%, 60.9%, and 34.2%) of the beam was changed by means of optical fibers of different lengths. The irradiated suspension was incubated at 37 degrees C for 30 min, and the attached cells were counted afterwards., Results: The cell fraction stimulated to adhere by red light at 637 nm was nearly the same in all three experimental groups (58.1% +/- 2.5%, 57.6% +/- 3.5%, and 62.5% +/- 3.2% for degree of beam polarization of 99.4%, 66.9%, and 34.2%, respectively). There was no statistically significant difference in these results (p <0.8, <0.6, and <0.7, respectively). At the same time, all three groups had statistically significant differences (p < 0.01) in adherence from the sham-irradiated control group (39.1% +/- 2.2%)., Conclusion: The biological effect (stimulation of cell attachment) of light with lambda = 637 nm on cells in our model system was pronounced, but did not depend on the degree of light polarization. Elementary processes in cells (light absorption and photochemistry) do not appear to depend on the degree of light polarization.

Objective: The aim of the present study was to compare the in vitro effects of the Er:YAG laser, an ultrasonic system, and manual curette on dentine root surface by roughness and micro-morphological analysis., Materials and Methods: Thirty-six flattened bovine roots were randomly assigned to one of the following groups: group 1 (n = 12): Er:YAG laser (2940 nm), 120 mJ/pulse, 10 Hz, 8.4 J/cm2; group 2 (n = 12): ultrasonic system; and group 3 (n = 12): manual curette. The mean surface roughness (Ra) of each sample was measured using a profilometer before and after the treatments. The micro-morphology of the treated and untreated (control) root surfaces was evaluated with scanning electron microscopy (SEM) at 50x and 1000x magnification., Results: Analysis with the profilometer showed that for equal times of instrumentation, the smoothest surfaces were produced by the Er:YAG laser and the ultrasonic system, followed by the curette (p < 0.05). Morphological analyses demonstrated that treatment with the Er:YAG laser produced some areas with an irregular surface, craters, and ablation of the intertubular dentin. The smear layer was removed and dentine tubules were opened by both curettes and the ultrasonic system. The micro-morphology of the dentine root surface after ultrasonic treatment, however, demonstrated randomly distributed areas cratering., Conclusion: All instruments increased the roughness of the dentine root surface after treatment; however, the curette produced rougher surfaces than the other devices. SEM analysis revealed distinct root surface profiles produced by the three devices.

Objective: This study aims to evaluate the influence of Nd:YAG and diode laser irradiation on apical sealing when applied before root canal filling done with two different resin-based cements (AH Plus and EndoREZ)., Background Data: Lasers have been widely used in endodontics. The morphologic changes in dentin walls caused by Nd:YAG and diode laser irradiation could improve sealing ability of endodontic cements., Methods: Eighty canine teeth were analyzed by apical leakage of methylene blue dye and by scanning electron microscope (SEM) images of the filling's adaptation to the apical third dentin walls. The laser irradiation parameters for the Nd:YAG laser were 100 mJ, 15 Hz, and 1.5 W, and for the diode laser was 2.5 W (continuous mode)., Results: The apical leakage results showed statistically significant differences at the 5% level of significance (Tukey's test, p < 0.05) among the different root canal wall treatments, independently of the root canal filling cement used. The cements also showed significant differences between them on the lased groups. The SEM analysis revealed better filling adaptation for AH Plus and the Nd:YAG laser group, confirming the microleakage results., Conclusion: We concluded that the combination of the Nd:YAG laser and AH Plus showed the best results.

Objective: The aim of this study was to observe and evaluate the micro-morphology of enamel and dentin surfaces after Er:YAG laser preparation and conditioning., Background Data: Information regarding micro-morphologic changes of tooth substance as a result of a change of Er:YAG laser parameters for cavity preparation is limited., Methods: Human enamel and dentin surfaces were irradiated with an Er:YAG laser with the following parameters : (1) energy output: 200 mJ, 250 mJ, 300 mJ, 350 mJ, and 400 mJ; (2) repetition rate: 5 Hz and 10 Hz; (3) pulse duration: 100 mus/VSP (very short pulse); (4) 5 and 10 passes over the surface at a distance of 7 mm, speed: 4 mm/s using a non-contact delivery tip; (5) water cooling: 5 mL/min. The hand piece was fixed in a power driven x-y moving table. Subsequently, half of the samples were laser-conditioned at 100 mJ, 10 Hz, 250 mus/SP (short pulse) for enamel, and 80 mJ, 10 Hz, SP for dentin at a distance of 10 mm. Surface morphology and surface alterations were evaluated using scanning electron microscopy (SEM)., Results and Conclusion: SEM evaluation showed the characteristics of Er:YAG-lased enamel and dentin surfaces: irregular enamel surfaces with typical keyhole shaped prisms and rods, and protrusion of dentinal tubules with a cuff-like appearance. Laser conditioning rounded off the sharp edges on the enamel irregularities and dentin surface structures. First signs of vitrification were seen at 250 mJ for enamel samples and 300 mJ for dentin samples. Increase of the pulse repetition rate from 5 Hz to 10 Hz did not result in changes of surface morphology. Laser conditioning did not result in additional vitrification.

Objective: The purpose of this study was to investigate the morphological change of dental hard tissue and surface roughness of cavities prepared by transversely excited, atmospheric pressure (TEA) CO2 laser irradiation., Background Data: It has been reported that dental hard tissues and bone can be removed by a long-pulse of TEA CO2 laser irradiation with minimal thermal damage. However, there are few reports on the surface roughness of lased teeth., Methods: The TEA CO2 laser was irradiated on the enamel and dentin surfaces of extracted human teeth under the following conditions: wavelength, 10.6 microm; output, 95 mJ/pulse; pulse repetition rate, 1 Hz; irradiation time, 7.5 microsec/shot; and energy density, 7.9 J/cm2. Morphological studies were performed by histological and scanning electron microscopic (SEM) examination. Surface roughness of prepared cavities was measured by three-dimensional laser microscopy., Results: Irradiated dentin produced a deeper defect (705 +/- 11 microm) than the enamel (501 +/- 10 microm). Histological appearance showed a basophilic line at the margin of lased dentin. SEM observation noted that the surfaces of the enamel cavity seem to be melted, and dentinal tubules were sealed. The surface roughness of the enamel cavity wall and dentin floor were 175 +/- 5 microm and 170 +/- 6 microm, respectively., Conclusion: These findings suggest that it is possible to remove carious dental hard tissue or cavity preparation with the TEA CO2 laser irradiation. Lased dental hard tissue can facilitate caries prevention, and surface roughness of the cavities might improve the bond strength of restorative dental materials.

Objective: The purpose of the present study was to investigate the tensile strengths of dentin after laser irradiation using three kinds of dental lasers to elucidate the laser-irradiation effect on dentin properties., Background Data: Different kinds of laser devices have been developed in dentistry. The characteristics of each laser are determined by its original wavelength; however, one common feature is to generate heat in irradiated tissues, and such heat possibly affects dentin collagen, which contributes to tensile strength of the tissues., Materials and Methods: Er:YAG, CO2, and diode (GaAlAs) lasers were used to irradiate bovine dentin. Subsequently, tensile test specimens were made from the irradiated dentin and tensile tests were conducted. The tensile strengths were analyzed using the paired-t test and Weibull analysis. Irradiated dentin was also observed transversally using light microscopy., Results: The tensile strengths of the lased dentin and the control group for the Er:YAG, CO2, and diode lasers were 73.1 and 78.5, 70.3 and 74.3, and 64.3 and 71.0 MPa, respectively. The tensile strength of the dentin had a tendency to decrease with laser irradiation. Weibull analysis indicated that the laser influence was different among the three kinds of laser apparatuses and seemed to correspond to the depths the laser beam reached, which were suggested by light microscopy observation., Conclusion: Laser irradiation could possibly decrease dentin tensile strength, which suggests the importance of careful use of laser for hard tissue treatment, considering its energy-transforming characteristics.