Ultrastructural changes of human dentin after irradiation by Nd:YAG laser

Effect of Remineralization Pretreatments on Human Dentin Permeability and Bond Strength

This study aimed to evaluate Nd:YAG laser, calcium phosphate, and adhesive system effect as different pretreatments in different protocols on dentin permeability (DP) and bond strength (BS). Fifty human dentin discs were used (4 mm in diameter and 1,5 mm in height). Specimens were divided into five groups (n = 10): (A): adhesive system (control); (AL): adhesive system + Nd:YAG laser; (LAL): Nd:YAG laser + adhesive system + Nd:YAG laser; (PAL): calcium phosphate-based dentin desensitizer TeethMate + adhesive system + Nd:YAG laser; and group (PLAL): Nd:YAG laser + calcium phosphate-based dentin desensitizer + adhesive system + Nd:YAG laser. All materials were used according to the manufacturers' instructions. The specimens were submitted to artificial aging (5,000 thermal cycles and 12 × 10⁴ mechanical cycles) then a bond test was performed. DP was measured using the split chamber model. Data were submitted to one-way analysis of variance (ANOVA), paired t-test, RM ANOVA, and Tukey test (p < 0.05). All treatments were effective in DP reduction. For BS, the groups PAL and PLAL had improved BS with a statistically significant difference of the control group (A). Nd:Yag laser irradiation and calcium phosphate-based desensitizing agents significantly reduced DP, and the association between them could improve the BS on resin-human dentin interface.

Effects of calcium-phosphate, laser and adhesive on dentin permeability and bond strength

Objectives

The present study examined a technique for reducing dentin permeability through the application of a calcium phosphate (CaP)-based desensitiser with a laser-assisted process and evaluated adhesive-dentin bond strength. Methods: Thirty dentin discs were divided into two groups according to whether the selected desensitiser (TeethMate; Kuraray Noritake) was used prior to dentin bonding. Each group was subdivided into three subgroups (n = 5): A- Adhesive (Single Bond Universal, 3M ESPE), AL- Adhesive + Laser (Nd:YAG 60 mJ) and LAL- Laser + Adhesive + Laser. Dentin permeability values (%) were recorded before and after desensitiser application. Resin composites were placed over the bonded specimens; the latter were aged prior to microtensile bond strength evaluation. Gelatinolytic activity within the hybrid layers was examined with in-situ zymography using confocal laser scanning microscopy. Data were analysed with ANOVA and Tukey test (α = 0.05).

Results

Significant differences in dentin permeability were identified for all groups (p = 0.00). Both laser treatment (p = 0.182) and desensitiser application (p = 0.687) did not significantly improve dentin bond strength. Ultrastructure of the resin-dentin interface identified presence of calcium phosphate within dentinal tubules. Laser treatment did not affect hybrid layer ultrastructure. Both treatment modalities (intratubular CaP occlusion and laser) had no influence on gelatinolytic activity within hybrid layers.

Conclusion

Although intratubular CaP occlusion and laser treatment were effective in reducing dentin permeability, they did not affect bond strength, interfacial ultrastructure and gelatinolytic activity within hybrid layers.

Clinical relevance

Treatment of etched dentin with Nd:YAG Laser at 60 mJ does not adversely affect collagen ultrastructure and gelatinolytic activity within the hybrid layer. The application of a calcium phosphate-based desensitiser to etch dentin does not affect dentin bond strength.

Scanning electron microscopy comparison of the cleaning efficacy of a root canal system by Nd:YAG laser and rotary instruments

This study evaluated the cleaning efficacy of a root canal system by Nd:YAG laser and rotary instruments. Sixty single-rooted human teeth were divided into four experimental groups (n=15). In the first group the teeth were prepared with a step-back technique using conventional K-files. In the second and third groups, tooth preparation was carried out using Nd:YAG laser and rotary NiTi instruments, respectively. Teeth in the fourth group were prepared by combined laser and rotary methods. The smear layer remaining on canal walls was then assessed by scanning electron microscopy in the coronal, middle, and apical portions. The comparison of smear layer removal efficacy between groups was carried out by Kruskal-Wallis and Mann-Whitney U tests. The mean grades of smear layer removal in rotary-laser, rotary, laser and step-back techniques were 1.34 ± 0.18, 2.2 ± 0.28, 1.91 ± 0.25, and 2.42 ± 0.19, respectively. On the whole, differences between rotary-laser and rotary groups, step-back, and the three other techniques (rotary, laser, and rotary-laser) were significant at p=0.034. Based on the findings of this study, the cleaning efficacy of rotary, laser, and rotary-laser techniques were better than the step-back technique and the combined laser and rotary technique was the most efficient method.

Morphological analysis of the resin-dentin interface in cavities prepared with Er,Cr:YSGG laser or bur in primary teeth

OBJECTIVE

The purpose of this study was to analyze the resin-dentin interface in cavities prepared with laser or bur in primary teeth.

BACKGROUND DATA

Erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser was expected to be an alternative cavity preparation method, enhancing surface alterations and producing morphological changes.

METHODS

Twenty extracted primary molar teeth were divided to four groups according to one of four cavity preparation and pretreatment regimens: Er,Cr:YSGG laser (G1), Er,Cr:YSGG laser+acid-etching (G2), bur (G3), and bur+acid-etching (G4). After applying composite resin to the cavities, the teeth were sectioned. The resin-dentin interface was analyzed under scanning electron microscopy (SEM) and ion analysis was performed with SEM-energy-dispersive X-ray spectroscopy (EDX) after immersion in ammoniacal silver nitrate solution.

RESULTS

In G1 and 2, the surfaces were wavy, and in G3 and 4, the surfaces were smooth. Microcracks were seen in some of the lased cavities. In G1 and 2, dentin tubules were exposed and there was lack of a smear layer. In G3, there were gaps and a smear layer in the resin-dentin interface, but no gaps or smear layer were observed in G4. In G2, the resin tags were increased, and some resin tags were broken in cavities, which were prepared with laser (G1 and 2).

CONCLUSIONS

According to the results of this study, acid-etching was recommended after laser preparations, to have a better adhesion.

Immediate and short-term effects of in-office desensitizing treatments for dentinal tubule occlusion

OBJECTIVE

The objective of this in vitro study was to evaluate the immediate and short-term effects of laser neodymium-doped yttrium aluminum garnet (Nd:YAG) irradiation and in-office desensitizing treatment on dentin tubule occlusion.

BACKGROUND DATA

Literature shows a lack of long-lasting treatments for dentin hypersensitivity.

METHODS

Forty-eight dentin slabs (4×4×2 mm) were ground flat, polished, and treated with 27% ethylenediaminetetraacetic acid (EDTA) to open the dentinal tubules. Specimens were randomly divided into the following experimental groups (n=12): Group 1: Control (no treatment); Group 2: Nd:YAG laser irradiation (100 mJ, 85 J/cm(2) per pulse with a quartz fiber of 400 μm, in scanning movements); Group 3: In-office prophylaxis with pumice; Group 4: In-office Colgate Sensitive Pro-Relief™ Desensitizing Paste. Treatments were performed according to the manufacturer's instructions. After treatment, the specimens were submitted to a sequence of erosive and abrasive challenges, twice a day for 5 days. The specimens were qualitatively and quantitatively evaluated by scanning electron microscopy immediately after treatment and after 4 and 5 days. The response variable was the amount of occluded dentin tubules per area, determined by three different examiners with the use of visual criteria, with a standardized grade created in the PowerPoint program. Data were compared with ANOVA and Tukey's test, considering a 5% significance level.

RESULTS

Immediately after treatment, a reduction in the number of opened dentin tubules was observed for the laser group when compared with the control group (p<0.05). After the experimental procedures, there were no quantitative differences between the amount of opened dentin tubules for all groups; however, micrographs showed some qualitative tubule occlusion for the laser group after the erosive/abrasive challenge.

CONCLUSIONS

only laser irradiation was capable of immediately sealing the dentinal tubules; however, none of the treatments showed efficacy in maintaining tubule occlusion after the chemical and mechanical challenges.

An in vitro evaluation of microtensile bond strength of resin-based sealer with dentin treated with diode and Nd:YAG laser

BACKGROUND

Smear layer is a negative factor which prevents adhesion of the filling material to the dentinal walls. Recent advances in dental research have incorporated lasers as a potential adjunct in root canal treatment by removing the smear layer before filling the root canal system, enhancing the adhesion of sealers to dentin and improving the sealing ability.

AIM

To evaluate the microtensile bond strength of AH-Plus resin-based sealer to dentin after treatment with 980 nm diode and 1,064 nm neodymium-doped:yttrium aluminum garnet (Nd:YAG) laser in vitro.

MATERIALS AND METHODS

Thirty specimens prepared for three groups namely group I (control), group II (980 nm diode-lased specimens) and group III (Nd:YAG-lased specimens). One tooth from each group was observed under scanning electron microscope for evaluation of intracanal root dentin morphology. Remaining specimens were used for making microsections by hard tissue microtome. Specimens for groups II and III were lased with 980 nm diode and 1,064 nm Nd:YAG laser. AH Plus sealer was applied onto specimens and mounted onto Instron universal testing machine for microtensile bond strength testing. Results were subjected to statistical analysis using one-way analysis of variance (ANOVA) and Tukey's test.

RESULTS

Group III Nd:YAG had maximum mean microtensile bond strength values (11.558 ± 0.869), followed by group II diode (9.073 ± 0.468) and group I control (6.05 ± 0.036). Statistically significant differences were seen among all the groups. SEM analysis shows removal of smear layer in both groups II and III.

CONCLUSION

Both Nd:YAG and diode laser were more effective than control group in improving the microtensile bond strength of AH Plus sealer to dentin.

CLINICAL SIGNIFICANCE

Lasers have the potential to increase the adhesiveness of root canal sealer to dentin surface, thereby improving the quality of root canal obturation.

Effect of Er,Cr:YSGG laser on human dentin fluid flow

The aim of the current investigation was to assess the rate and magnitude of dentin fluid flow of dentinal surfaces irradiated with Er,Cr:YSGG laser. Twenty extracted third molars were sectioned, mounted, and irradiated with Er,Cr:YSGG laser at 3.5 and 4.5 W power settings. Specimens were connected to an automated fluid flow measurement apparatus (Flodec). The rate, magnitude, and direction of dentin fluid flow were recorded at baseline and after irradiation. Nonparametric Wilcoxon signed ranks repeated measure t test revealed a statistically significant reduction in fluid flow for all the power settings. The 4.5-W power output reduced the flow significantly more than the 3.5 W. The samples showed a baseline outward flow followed by inward flow due to irradiation then followed by decreased outward flow. It was concluded that Er,Cr:YSGG laser irradiation at 3.5 and 4.5 W significantly reduced dentinal fluid flow rate. The reduction was directly proportional to power output.

Micromorphology of resin-dentin interfaces using one-bottle etch&rinse and self-etching adhesive systems on laser-treated dentin surfaces: a confocal laser scanning microscope analysis

BACKGROUND AND OBJECTIVES

This study evaluated the hybrid layer (HL) morphology created by three adhesive systems (AS) on dentin surfaces treated with Er:YAG laser using two irradiation parameters.

STUDY DESIGN

Occlusal flat dentin surfaces of 36 human third molars were assigned into nine groups (n = 4) according to the following ASs: one bottle etch&rinse Single Bond Plus (3M ESPE), two-step Clearfil Protect Bond (Kuraray), and all-in-one S(3) Bond (Kuraray) self-etching, which were labeled with rhodamine B or fluorescein isothiocyanate-dextran and were applied to dentin surfaces that were irradiated with Er:YAG laser at either 120 (38.7 J/cm(2)) or 200 mJ/pulse (64.5 J/cm(2)), or were applied to untreated dentin surfaces (control group). The ASs were light-activated following MI and the bonded surfaces were restored with resin composite Z250 (3M ESPE). After 24 hours of storage in vegetable oil, the restored teeth were vertically, serially sectioned into 1-mm thick slabs, which had the adhesive interfaces analyzed with confocal laser microscope (CLSM-LSM 510 Meta). CLSM images were recorded in the fluorescent mode from three different regions along each bonded interface.

RESULTS

Non-uniform HL was created on laser-irradiated dentin surfaces regardless of laser irradiation protocol for all AS, while regular and uniform HL was observed in the control groups. "Stretch mark"-like red lines were found within the HL as a result of resin infiltration into dentin microfissures, which were predominantly observed in 200 mJ/pulse groups regardless of AS. Poor resin infiltration into peritubular dentin was observed in most regions of adhesive interfaces created by all ASs on laser-irradiated dentin, resulting in thin resin tags with neither funnel-shaped morphology nor lateral resin projections.

CONCLUSION

Laser irradiation of dentin surfaces at 120 or 200 mJ/pulse resulted in morphological changes in HL and resin tags for all ASs evaluated in the study.

Root surface biomodification with Nd:YAG laser for the treatment of gingival recession with subepithelial connective tissue grafts

BACKGROUND/AIM

Root surface biomodification has been used to treat gingival recession and periodontitis. The principle for this procedure is that removing the smear layer from the root surfaces exposes collagen fibers, which leads to improved healing. Clinical studies generally have failed to find any improvement in clinical parameters when using such procedures, however. The aim of this study was to evaluate and compare the outcome of gingival recession therapy using the subepithelial connective tissue graft (SCTG) with or without Nd:YAG laser application for root surface biomodification.

MATERIALS AND METHODS

Thirty-four teeth in 17 patients with Miller Class 1 and 2 recession were treated with SCTG with (test group) or without (control group) the application of Nd:YAG laser (1 W, 10 Hz, 100 mj, 60 s, 1064 nm). Clinical attachment level (CAL), recession depth (RD), recession width (RW), and probing depth (PD) were measured at baseline and six months postsurgery.

RESULTS

Both treatments yielded significant improvements in terms of RD and RW decrease and CAL gain compared to baseline values. For test and control groups, the average root coverage was 33% and 77%, respectively (p < 0.05), and the complete root coverage was 18% and 65%, respectively (p < 0.05). The control group showed a greater reduction in RD and RW compared with the test group (p < 0.05).

CONCLUSIONS

The use of Nd:YAG laser as a root surface biomodifier negatively affected the outcome of root coverage with the SCTG.

CO(2), Er: YAG and Nd:YAG lasers in endodontic surgery

Objectives:

CO₂, Er:YAG and Nd:YAG lasers have been used in endodontic surgery. This in vitro study evaluated 1% Rhodamine B dye penetration using computer-assisted morphometry (ImageTool Software®) of 108 endodontically treated human permanent canines.

Material and methods:

Teeth were divided into 9 groups according to the technique used: A: 90-degree apicoectomy with bur, root-end cavity preparation with ultrasound and filled with MTA; B: 90-degree apicoectomy with bur, root-end cavity prepared with ultrasound and filled with MTA, and treatment of apical surface with CO₂ laser (1 W, CW/CW); C: 90-degree apicoectomy with bur, and treatment of apical surface with Nd:YAG laser (150 mJ, 10 Hz); D: 90-degree apicoectomy with bur, and treatment of apical surface with CO₂ laser (1 W, CW/CW); E: apicoectomy with Er:YAG laser (400 mJ, 10 Hz), root-end cavity prepared with ultrasound and filled with MTA; F: apicoectomy with Er:YAG laser (400 mJ, 10 Hz) and treatment of apical surface with Nd:YAG laser (150 mJ, 10Hz); G: apicoectomy with CO₂ laser (5W, CW/SP), root-end cavity prepared with ultrasound and filled with MTA; H: irradiation of apical end with CO₂ laser (1 W, CW/CW); I: irradiation of apical end with Nd:YAG laser (150 mJ, 10 Hz).

Results:

Dye penetration was found in all specimens at different rates, the lowest penetration occurring in groups C (16.20%), B (17.24%) and F (17.84%).

Conclusions:

Groups B, C and F represent the best technical sequences to perform endodontic surgery.

Evaluation of the furcation area permeability of deciduous molars treated by neodymium:yttrium-aluminum-garnet laser or adhesive

The purpose of this in vitro study was to compare the effects of a self-etch adhesive system and neodymium:yttrium-aluminum-garnet (Nd:YAG) laser application on the dentinal permeability of the furcation area of primary molars. After endodontic access, 39 extracted human deciduous molars were divided into three groups: control group (CG), no treatment; adhesive group (AG), self-etching adhesive was applied to the furcation area; laser group (LG), specimens were irradiated with Nd:YAG laser. To evaluate dentin permeability of the furcation area, we immersed the specimens in 0.5 % methylene blue dye for 4 h. Then, they were longitudinally sectioned into two halves and photographed. The images were analyzed by two qualified evaluators using TpsDig software to calculate the percentage of the dye penetration area in comparison with the total furcation area. Additional analyses by scanning electron microscopy (SEM) were performed. The analysis of variance (ANOVA), complemented by Student's t-test, showed that mean dye penetration in the LG was statistically significant lower than that in all the other groups (P < 0.05). The SEM analysis showed mostly dentinal tubules obliterated by smear layer in the CG; in the AG the smear layer was modified by the adhesive, and, in the LG, melted surfaces were observed. It can be concluded that the Nd:YAG laser was capable of reducing the dentinal permeability of the furcation area of deciduous molars.

In vitro study of root fracture treated by CO2 laser and DP-bioactive glass paste

BACKGROUND/PURPOSE

An ideal material has yet to be discovered that can successfully treat vertical root fracture. Therefore, the purpose of this study was to use a continuous-wave CO2 laser of medium-energy density to fuse DP-bioactive glass paste (DPGP) to vertical root fracture.

METHODS

The DP-bioglass powder was based on a Na2O-CaO-SiO2-P2O5 system and it was mixed with phosphoric acid (65% concentration) with a powder/liquid ratio of 2 g/4 mL to form DPGP. The interaction of DPGP and dentin was analyzed by means of X-ray diffractometer (XRD) and differential thermal analysis/thermogravimetric analysis (DTA/TGA). Root fracture line was filled with DPGP followed by CO2 laser irradiation and the result was examined by scanning electron microscopy (SEM).

RESULTS

The main crystal phase of DPGP was monocalcium phosphate monohydrate (Ca(H2PO4)2.H2O) and the phase transformed to dicalcium phosphate dihydrate (CaHPO4.2H2O) after mixing DPGP with dentin powder (DPG-D). Additionally, gamma-Ca2P2O7 and beta-Ca2P2O7 were identified when DPG-D was lased by CO2 laser. The reaction temperature was between 500 degrees C and 1100 degrees C. SEM results demonstrated that the fracture line was effectively sealed by DPGP.

CONCLUSION

The chemical reaction of DPGP and dentin indicated that DPGP combined with CO2 laser is a potential regimen for the treatment of vertical root fracture.

Effects of Er:YAG laser and Nd:YAG laser treatment on the root canal dentin of human teeth: a SEM study

The objective of the study was to observe the morphological changes on root canal dentin after Er:YAG laser and Nd:YAG laser treatment. Twenty-one teeth biomechanically prepared were divided into three groups with seven teeth of each. Group A was unlased as a control. In group B, Er:YAG laser and in group C, Nd:YAG laser was applied to the root canal dentin. The roots were split longitudinally and examined using a scanning electron microscopy for the evaluation of debris, smear layer, and recrystallization. There was no statistically significant difference between the groups. This study indicates that laser beam is not effective in removing debris and smear layer.

Microstructural changes of enamel, dentin-enamel junction, and dentin induced by irradiating outer enamel surfaces with CO2 laser

The microstructural changes of enamel, dentin-enamel junction (DEJ), and dentin after CO(2) laser irradiation were studied. Buccal enamel surfaces of human third molars about 2 mm from the DEJ were irradiated, and the laser tip was moved 5 mm in a mesiodistal direction with 5 s of irradiation time. The output powers were 2 to 10 W in a continuous mode, and the average doses were approximately from 250 to 1,250 J/cm(2). All specimens were examined by a scanning electron microscope, and heat-transfer simulation was also applied to calculate temperature distribution. Surface ablation of enamel and separation of enamel and dentin along the DEJ were observed when the laser power output exceeded 3 W. Heat-transfer simulation indicated that dentin was prone to store more thermal energy than enamel. In conclusion, operation parameters of the CO(2) laser should be carefully selected to avoid thermal damage to the DEJ.

Tensile bond strength of Er,Cr:YSGG laser-irradiated human dentin and analysis of dentin-resin interface

OBJECTIVES

As the bond strength of composite resin to Er,Cr:YSGG laser-irradiated dentin has not yet been evaluated, the objectives of this study were to investigate the tensile bond strength and to analyze the resin-dentin interface among bur-cut/acid-etched, Er,Cr:YSGG laser-ablated/acid-etched and Er,Cr:YSGG laser-ablated human dentin.

METHODS

Crown dentin disks prepared from extracted human third permanent molars were used for the observation of surface morphological changes by scanning electron microscope (SEM). The laser energy parameters were 3.5 W and 20 Hz with water spray (air pressure level, 80%; water pressure level, maximum level). Another group of crown dentin disks were prepared for composite resin restoration and observation of resin-dentin bond interface after demineralization in 6N hydrochloric acid (HCl) for 1 min and deproteinization in 1% sodium hypochlorite solution (NaOCl) for 10 min. The tensile bond strengths of the three groups were measured by a universal testing machine at a crosshead speed of 0.5 mm/min. Fracture types at the dentin-resin interface were analyzed using the digital stereoscopic microscope and fractured surfaces of the debonded specimens were examined by SEM.

RESULTS

All three groups showed that the treated surfaces were free of dentin debris and smear layer. The peritubular dentin protruded from the surrounding intertubular dentin after laser irradiation. The dentin-resin interface treated with Er,Cr:YSGG laser irradiation and acid etching demonstrated numerous resin tags converging into a bulge and then diverging again. The length of resin tags was greater than 100 microm. The tensile bond strengths of bur-cut/acid-etched, laser-ablated/acid-etched and laser-ablated human dentin were 5.37+/-1.51, 5.17+/-1.41 and 3.29+/-0.86 MPa, respectively. No statistical significance was found between the bur-cut/acid-etched and laser-ablated/acid-etched groups. The predominant fracture modes of bur-cut/acid-etched, laser-ablated/acid-etched and laser-ablated human dentin were Type 1 (50%), Type 2 (70%) and Type 1 (70%), respectively.

SIGNIFICANCE

Er,Cr:YSGG laser irradiation affects adversely adhesion of resin to dentin but acid etching following laser irradiation could increase the tensile bond strength as high as that of bur-cut/acid-etched human dentin.

Effects of Er:YAG and Nd:YAG lasers on dentin permeability in root surfaces: a preliminary in vitro study

OBJECTIVE

This in vitro study evaluated the effects of Nd:YAG and Er:YAG lasers on reducing dentin permeability by sealing opened tubules.

BACKGROUND DATA

According to hydrodynamic theory, dentine hypersensitivity occurs when dentin is exposed with tubules opened. Consequently, a painful sensation occurs due to an intensification of the dentinal permeability. Treatment, therefore, should be based on a decrease of this permeability, achieved by the obliteration of dentinal tubules. The Nd:YAG laser is known for its capacity to seal dentinal tubules; however, few studies concerning treatment with Er:YAG laser are available.

METHODS

The Nd:YAG laser was used, based on two parameters: (A) 1.0 W, 10 Hz, and (B) 1.5 W, 15 Hz. The Er:YAG laser was used at 60 mJ, 2 Hz, four applications of 20 sec each, at 6 mm from the surface. After irradiation, all samples were immersed in 1% Rodamine B dye solution, in order to evaluate the penetration of the dye solution and observe the decrease/increase of dentinal permeability after the laser treatment.

RESULTS

The laser conditions used in the present study decreased the permeability as follows: (a) when using the Er:YAG laser at 60 mJ, 2 Hz in 26.05%, and (b) when using the Nd:YAG laser at 1.5 W, 15 Hz in 19.03%--with no statistical difference between them. Additionally, the Nd:YAG laser at 1.0 W, 10 Hz, decreased permeability in 4.59%, with a smaller effect.

CONCLUSIONS

According to the results of this in vitro study, the Er:YAG laser at 60 mJ, 2 Hz, and the Nd:YAG laser at 1.5 W, 15 Hz are useful for decreasing dentin permeability.

Er:YAG laser treatments on dentine surface: micro-Raman spectroscopy and SEM analysis

OBJECTIVE

This study aims to give an insight into the chemical and structural modifications occurring in laser treated dentine surface, as a tool to plan a new class of dental materials specific for the dental restoration when laser technologies are used. For this purpose the effect of Er:YAG (Erbium-Yttrium Aluminium Garnet) laser treatments on human dentine surface has been investigated.

METHODS

The dentine surface of periodontally compromised teeth cut along the main axis was treated in vitro with laser pulses having the same energy but time duration varying in the range of 100-1000 micros. The chemical characteristics and the morphology of the laser treated surface have been studied with micro-Raman spectroscopy (micro-RS) and scansion electron microscopy (SEM).

RESULTS

The micro-RS and SEM analysis of laser treated teeth have been compared with those of surfaces treated with conventional mechanical methodologies. The laser pulse time duration affects the surface morphology and the chemistry of dentine, mainly of organic components. The effects have been monitored by analysing the C-H group stretch vibration mode of the micro-RS spectrum.

CONCLUSION

The laser treatment can determine different chemical microenvironments on the treated dentine surface, depending on the time duration of laser pulse used. Treatments with very long pulse results in a the dentine surface very similar to that obtained with a conventional mechanical drill, while with very short laser pulses a strong modification of the dentine organic components has been observed.

Structural Changes of Er:YAG Laser–Irradiated Human Dentin

OBJECTIVE

The aim of this study was to investigate the phase, compositional, and morphological changes of Er:YAG laser-irradiated dentin.

BACKGROUND DATA

To date, nothing comprehensive has been reported about the phase and compositional changes of human dentin after Er:YAG laser irradiation.

METHODS

The human dentin was irradiated by Er:YAG laser with irradiation energies from 300 mJ/pulse-10 pps-10 sec to 700 mJ/pulse-10 pps-10 sec with and without water spray. After irradiation, the specimens were analyzed by means of x-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).

RESULTS

After exposure to Er:YAG laser, dentin showed no phase changes on the x-ray diffractometer. In Fourier transform infrared analysis, two absorption bands at 2200 and 2015 cm(-1) could be traced on dentin treated by Er:YAG laser with irradiation energies beyond 300 mJ/pulse-10 pps-10 sec and without water spray. The OH(-) band disappeared at 1630 cm(-1). Scanning electron micrographs revealed that laser energy of 500 mJ/pulse-10 pps-10 sec was sufficient to prompt melting and recrystallization of dentin crystals.

CONCLUSIONS

Our study demonstrated that Er:YAG laser irradiation on dentin with water spray would not significantly change the structure and composition. Therefore, water cooling is important for reducing the thermal effect of Er:YAG laser.

Safety parameters for pulp temperature during selective ablation of caries by KTP laser in vitro

OBJECTIVE

To define the optimal parameters of KTP laser irradiation during a selective caries removal.

MATERIALS AND METHODS

Twelve decayed human teeth, recently extracted were used. Their root canals were prepared for insertion of a thermocouple probe into the pulp chamber. The demineralized tissues were colored by Acid Red 52 before proceeding to different conditions of irradiation.

RESULTS

Pulpal temperature increases (below 3 degrees C) were found under the following parameters with 15 sec of continuous lasing: 400 mWatts, 0.10-msec pulse width, PRR <50 Hz for efficient caries removal. A resting time average of 70 sec was necessary to allow pulp temperature to get back to its baseline.

CONCLUSION

KTP laser can be used safely and without any pulp over-heating under certain irradiation conditions.