Influence of pulse repetition rate on temperature rise and working time during composite filling removal with the Er : YAG laser

Objective: The purpose of this study was to assess the efficacy of Er:YAG laser energy for composite resin removal and the influence of pulse repetition rate on the thermal alterations occurring during laser ablation. Materials and Methods: Composite resin filling was placed in cavities (1.0 mm deep) prepared in bovine teeth and the specimens were randomly assigned to five groups according to the technique used for composite filling removal. In group I (controls), the restorations were removed using a high-speed diamond bur. In the other groups, the composite fillings were removed using an Er: YAG laser with different pulse repetition rates: group 2-2 Hz; group 3-4 Hz; group 4-6 Hz; and group 5-10 Hz. The time required for complete removal of the restorative material and the temperature changes were recorded. Results: Temperature rise during composite resin removal with the Er: YAG laser occurred in the substrate underneath the restoration and was directly proportional to the increase in pulse repetition rate. None of the groups had a temperature increase during composite filling removal of more than 5.6 degrees C, which is considered the critical point above which irreversible thermal damage to the pulp may result. Regarding the time for composite filling removal, all the laser-ablated groups (except for group 5 [10 Hz]) required more time than the control group for complete elimination of the material from the cavity walls. Conclusion: Under the tested conditions, Er: YAG laser irradiation was efficient for composite resin ablation and did not cause a temperature increase above the limit considered safe for the pulp. Among the tested pulse repetition rates, 6 Hz produced minimal temperature change compared to the control group (high-speed bur), and allowed composite filling removal within a time period that is acceptable for clinical conditions.

Effect of Er:YAG Laser Parameters on Ablation Capacity and Morphology of Primary Enamel

Objective: The purpose of this study was to evaluate the ablation capacity of different energies and pulse repetition rates of Er:YAG laser energy on primary molar enamel, by assessing mass loss and by analyzing the surface morphology with scanning electron microscopy. Background Data: Previous studies have demonstrated the capacity of the Er:YAG laser to ablate enamel substrate. Methods: Forty-two sound primary molars were bisected in a mesiodistal direction. The enamel surfaces were flattened and their initial mass (in milligrams) was obtained. An area of 4 mm(2) was delimited. The specimens were randomly assigned to 12 groups according to the combination of energy (160, 200, 250, and 300 mJ) and pulse repetition rate (2, 3, and 4 Hz). Er: YAG laser irradiation was performed on each specimen for 20 sec. After irradiation, the final mass was obtained and specimens were prepared for examination with scanning electron microscopy. The data obtained by subtracting the final mass from the initial mass were statistically analyzed using ANOVA and the Tukey test (p < 0.05). Results: The pulse repetition rate of 4 Hz provided greater mass loss, different from that seen with 2 Hz, and similar to that seen with 3 Hz. The energy level of 300 mJ resulted in greater mass loss, similar to that seen with 200 and 250 mJ. Scanning electron photomicrographs showed that there was non-selective enamel removal, with fused and cracked areas in all specimens. Conclusion: The parameters of 200 mJ and 2 Hz produced a good ablation rate with fewer surface alterations in primary molar enamel.

Thermal lens and heat generation of Nd : YAG lasers operating at 1.064 and 1.34 mu m

We report on a simple and accurate method for determination of thermo-optical and spectroscopic parameters (thermal diffusivity, temperature coefficient of the optical path length change, pump and fluorescence quantum efficiencies, thermal loading, thermal lens focal length, etc) of relevance in the thermal lensing of end-pumped neodymium lasers operating at 1.06- and 1.3-mu m channels. The comparison between thermal lensing observed in presence and absence of laser oscillation has been used to elucidate and evaluate the contribution of quantum efficiency and excited sate absorption processes to the thermal loading of Nd: YAG lasers. (c) 2008 Optical Society of America.

Microstructuration induced differences in the thermo-optical and luminescence properties of Nd:YAG fine grain ceramics and crystals

The temperature and compositional dependences of thermo- optical properties of neodymium doped yttrium aluminum garnet (YAG) crystals and fine grain ceramics have been systematically investigated by means of time- resolved thermal lens spectrometry. We have found that Nd:YAG ceramics show a reduced thermal diffusivity compared to Nd:YAG single crystals in the complete temperature range investigated (80-300 K). The analysis of the time- resolved luminescent properties of Nd(3+) has revealed that the reduction in the phonon mean free path taking place in Nd:YAG ceramics cannot be associated with an increment in the density of lattice defects, indicating that phonon scattering at grain boundaries is the origin of the observed reduction in the thermal diffusivity of Nd: YAG ceramics. Finally, our results showed the ability of the time- resolved thermal lens to determine and optimize the thermo- optical properties of Nd: YAG ceramic based lasers. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2975335]

Mechanical strength evaluation for Nd-YAG laser and electric resistance spot weld (ERSW) joint under multiaxial loading

This work presents a comparison between laser weld (LBW) and electric resistance spot weld (ERSW) processes used for assemblies of components in a body-in-white (BIW) at a world class automotive industry. It is carried out by evaluating the mechanical strength modeled both by experimental and numerical methods. An ""Arcan"" multiaxial test was designed and manufactured in order to enable 0 degrees, 45 degrees and 90 degrees directional loadings. The welded specimens were uncoated low carbon steel sheets (S-y = 170 MPa) used currently at the automotive industry, with two different thicknesses: 0.80 and 1.20 mm. A numerical analysis was carried out using the finite element method (FEM) through LS-DYNA code. (c) 2007 Elsevier B.V. All rights reserved.

Influence of Er:YAG Laser Frequency on Dentin Caries Removal Capacity

The purposes of this study were to evaluate in vitro the influence of different frequencies of Er:YAG laser on the human dentin caries removal capacity. Thirty fragments obtained from third molars were randomly assigned into three groups (n = 10) according to the laser frequency used: 4, 6, and 10 Hz. The caries lesion (+/-1 mm deep) was induced before the irradiation by S. mutans cultures for 6 weeks. The specimens of all groups were irradiated with 200 mJ of energy in noncontact and focused mode under constant refrigeration (water flow: 2.5 mL/min). Quantitative analysis of the caries removal was performed by DIAGNOdent (TM) and the Axion Vision (TM) software. Qualitative analysis was performed by Scanning electron microscope (SEM) and light microscope (LM). Data were analyzed by ANOVA and Fishers` tests. The DIAGNOdent (TM) revealed that the caries removal was similar with 4 and 6 Hz and was superior with 10 Hz (P < 0.05). The analysis with Axion Vision (TM) software revealed that the caries removal was similar with 6 and 10 Hz and the 4 Hz group promoted the lowest caries removal. Through SEM morphologic analysis, some specimens irradiated with 4 Hz presented, under the demineralized dentin, a disorganized collagenous matrix. The LM images revealed that all frequencies used promoted irregular caries removal, being observed over preparations with 6 and 10 Hz. It can be concluded that the increase of Er:YAG laser frequency provided a higher dentin caries removal without selectivity to the disorganized dentin. Microsc. Res. Tech. 74:281-286, 2011. (C) 2010 Wiley-Liss, Inc.

Selectively excited luminescence and magnetic circular dichroism of Cr4+-doped YAG and YGG

Site selective luminescence and magnetic circular dichroism experiments on Cr4+-doped yttrium aluminum garnet and yttrium gallium garnet have been made at low temperature. The spectral assignments for these near-IR lasing materials have been made using experimental data and ligand field calculations guided by the known geometry of the lattices. [S0163-1829(99)07003-4].

Bond strength of an adhesive system irradiated with Nd : YAG laser in dentin treated with Er : YAG laser

The purpose of this in vitro study was to verify through micro tensile bond test the bond strength of an adhesive system irradiated with Nd:YAG laser in dentine previously treated with Er:YAG laser. Twenty caries free extracted human third molars were used. The teeth were divided in four experimental groups (n = 5): (G1) control group; (G2) irradiation of the adhesive system with the Nd:YAG laser; (G3) dentin treatment with Er:YAG laser; (G4) dentin treatment with Er:YAG laser followed by the irradiation of the adhesive system with Nd:YAG laser. The Er:YAG laser fluency parameter for the dentin treatment was of 60 J/cm(2). ne adhesive system was irradiated with the Nd:YAG laser with fluency of 100 J/cm(2). Dental restorations were performed with Adper Single Bond 2/Z250. One tooth from each group was prepared for the evaluation of the adhesive interface under SEM and bond failure tests were also performed and evaluated. The statistical analysis showed statistical significant difference between the groups G1 and G3, G1 and G4, G2 and G3, and G2 and G4; and similarity between the groups G1 and G2, and G3 and G4. The adhesive failures were predominant in all the experimental groups. The SEM analysis showed an adhesive interface with features confirming the results of the mechanical tests. The Nd:YAG laser on the adhesive system did not influence the bond strength in dentin treated or not with the Er:YAG laser.

Comparison of Preoperative Nd:YAG Laser Anterior Capsulotomy Versus Two-Stage Curvilinear Capsulorhexis in Phacoemulsification of White Intumescent Cataracts

BACKGROUND AND OBJECTIVE: To compare the results of preoperative Nd:YAG laser anterior capsulotomy versus two-stage continuous curvilinear capsulorhexis (CCC) in phacoemulsification of eyes with white intumescent cataracts and liquefied cortex. PATIENTS AND METHODS: Twenty-three eyes with white intumescent cataract were consecutively randomized for phacoemulsification with preoperative Nd:YAG laser anterior capsulotomy (group 1, n = 11) or two-stage CCC (group 2, n = 12) procedures. Intraoperative findings and postoperative outcomes were compared using the nonparametric tests. RESULTS: Postoperative Visual acuity, mean surgical time, mean effective phacoemulsification time, and frequency of complications were not significantly different between the two groups (P > .05). Two cases in each group were converted to the extracapsular technique. Excluding these four patients, surgical time was shorter In group 1 (P = .017). CONCLUSION: Preoperative Nd:YAG laser anterior capsulotomy is a safe technique in decompressing the capsular bag before phacoemulsification of white intumescent cataracts with liquefied cortex.

Morphological assessment of dentine and cementum following apicectomy with Zekrya burs and Er:YAG laser associated with direct and indirect Nd:YAG laser irradiation

Objectives. This study aimed to assess the apical surface morphology of maxillary central incisors resected 3.0 mm from the tooth apex using Zekrya burs or Er:YAG laser, with or without subsequent direct Nd:YAG laser irradiation (apical and buccal surfaces) and indirect irradiation (palatal surface). Study design. Forty maxillary central incisors were instrumented and obturated. The roots were divided into 4 groups according to the root resection method (Zekrya bur or Er: YAG laser -1.8 W, 450 mJ, 4 Hz, 113 J/cm(2)) and further surface treatment (none or Nd: YAG laser -2.0 W, 100 mJ, 20 Hz, 124 J/cm(2)). The teeth were prepared for SEM analysis. Scores ranging from 1 to 4 were attributed to cut quality and morphological changes. The data were analyzed by the Kruskal-Wallis test and by Dunn`s test. Results. SEM images showed irregular surfaces on the apical portions resected with Zekrya burs, with smear layer and grooves in the resected dentine and slight gutta-percha displacement and plasticization. On the other hand, apicectomies carried out with Er: YAG laser showed morphological changes compatible with ablated dentine, with rough surfaces and craters. In spite of the presence of plasticized gutta-percha, with the presence of bubbles, an irregular adaptation of the filling material to the root walls was also observed. Direct Nd: YAG laser irradiation of the apical and buccal surfaces of the resected roots resulted in areas of resolidification and fusion in the dentine and cementum, with a vitrified aspect; indirect Nd: YAG laser irradiation of the palatal surfaces yielded a lower number of changes in the cementum, with irregular resolidification areas. Conclusions. There were no differences in terms of cut quality between the use of burs and Er: YAG laser or between the 2 surfaces (apical and buccal) treated with Nd: YAG laser with direct irradiation. However, morphological changes were significantly less frequent on surfaces submitted to indirect irradiation (palatal) when compared with those directly irradiated. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010; 109: e77-e82)

In Vitro Microleakage of Composite Restorations Prepared by Er:YAG/Er,Cr:YSGG Lasers and Conventional Drills Associated with Two Adhesive Systems

Purpose: The objective of this in vitro study was to compare the degree of microleakage of composite restorations performed by lasers and conventional drills associated with two adhesive systems. Materials and Methods: Sixty bovine teeth were divided into 6 groups (n = 10). The preparations were performed in groups 1 and 2 with a high-speed drill (HID), in groups 3 and 5 with Er:YAG laser, and in groups 4 and 6 with Er,Cr:YSGG laser. The specimens were restored with resin composite associated with an etch-and-rinse two-step adhesive system (Single Bond 2 [SB]) (groups 1, 3, 4) and a self-etching adhesive (One-Up Bond F [OB]) (groups 2, 5, 6). After storage, the specimens were polished, thermocycled, immersed in 50% silver nitrate tracer solution, and then sectioned longitudinally. The specimens were placed under a stereomicroscope (25X) and digital images were obtained. These were evaluated by three blinded evaluators who assigned a microleakage score (0 to 3). The original data were submitted to Kruskal-Wallis and Mann-Whitney statistical tests. Results: The occlusal/enamel margins demonstrated no differences in microleakage for all treatments (p > 0.05). The gingival/dentin margins presented similar microleakage in cavities prepared with Er:YAG, Er,Cr:YSGG, and HD using the etch-and-rinse two-step adhesive system (SB) (p > 0.05); otherwise, both Er:YAG and Er,Cr:YSGG lasers demonstrated lower microleakage scores with OB than SB adhesive (p < 0.05). Conclusion: The microleakage score at gingival margins is dependent on the interaction of the hard tissue removal tool and the adhesive system used. The self-etching adhesive system had a lower microleakage score at dentin margins for cavities prepared with Er:YAG and Er,Cr:YSGG than the etch-and-rinse two-step adhesive system.

Effects of Nd:YAG Laser Irradiation on the Hybrid Layer of Different Adhesive Systems

Purpose: The aim of this in vitro study was to evaluate the microtensile bond strength (mu TBS) and hybrid layer morphology of different adhesive systems, either followed by treatment with Nd:YAG laser irradiation or not. Previous studies have shown the effects of Nd:YAG laser irradiation on the dentin surface at restoration margins, but there are few reports about the significance of the irradiation on the hybrid layer. Materials and Methods: The flattened coronal and root dentin samples of 24 bovine teeth were randomly divided into 8 groups, according to the adhesive system used - Scotchbond Multi Purpose (SBMP) or Clearfil SE Bond (CSEB) - and were either irradiated with Nd:YAG or not, with different parameters: 0.8 W/10 Hz, 0.8 W/20 Hz, 1.2 W/10 Hz, 1.2 W/20 Hz. The left sides of specimens were the control groups, and right sides were irradiated. A composite crown was built over bonded surfaces and stored in water (24 h at 37 degrees C). Specimens were sectioned vertically into slabs that were subjected to mu TBS testing and observed by SEM. Results: Control groups (27.81 +/- 1.38) showed statistically higher values than lased groups (21.37 +/- 0.99), and CSEB control group values (31.26 +/- 15.71) were statistically higher than those of SBMP (24.3 +/- 10.66). There were no significant differences between CSEB (20.34 +/- 10.01) and SBMP (22.43 +/- 9.82) lased groups. Among parameters tested, 0.8 W/10 Hz showed the highest value (25.54 +/- 11.74). Nd:YAG laser irradiation caused dentin to melt under the adhesive layer of both adhesive systems tested. Conclusion: With the parameters used in this study, Nd:YAG laser irradiation of the hybrid layer promoted morphological changes in dentin and negatively influenced the bond strength of both adhesive systems.

Influence of the Additional Er:YAG Laser Conditioning Step on the Microleakage of Class V Restorations

The purpose of this study was to evaluate the influence of an additional Er:YAG laser conditioning step after laser cavity preparations, on the microleakage of class V composite restorations. Forty-eight bovine incisors were randomly divided into four groups: G1(control) cavities prepared with bur, G2- cavities prepared with laser (400 mJ/2 Hz), G3-cavities prepared and subsequently conditioned with Er:YAG laser (60 mJ/2 Hz); G4-idem for G3, but the laser conditioning was carried out without water-spray. All the cavities were restored using Clearfill SE Bond (R) and Z-250 (R) composite resin. The samples were thermal cycled for 700 cycles and then immersed in 50% silver nitrate solution. The sectioned restorations were exposed to a photoflood lamp to reveal silver nitrate penetration. The Kruskal-Walis one-way analyses of variance test and post hoc Wilcoxon pair-wise comparison were used to compare microleakage degrees. At the gingival margin G2 showed a lower microleakage mean than the control bur-prepared cavities (p = 0.0003). At occlusal margins there were no statistically significant differences between the groups (p = 0.28). It may be concluded that Er:YAG laser class V cavity preparations do not need to be followed by an additional laser conditioning step to result in levels of microleakage similar to or lower than those obtained after bur preparations. (C) 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 87B: 538-543, 2008

Micro-shear bond strength of Er : YAG-laser-treated dentin

This study tested if dentin adhesion is affected by Er:YAG laser. Ninety dentin disks were divided in groups (n=10): G1, control; G2, Er:YAG laser 150 mJ, 90 degrees contact, 38.8 J/cm(2); G3, Er:YAG laser 70 mJ, 90 degrees contact, 18.1 J/cm(2); G4, Er:YAG laser 150 mJ, 90 degrees non-contact, 1.44 J/cm(2); G5, Er:YAG laser 70 mJ, 90 degrees non-contact, 0.67 J/cm(2); G6, Er:YAG laser 150 mJ, 45 degrees contact, 37.5 J/cm(2); G7, Er:YAG laser 70 mJ, 45 degrees contact, 17.5 J/cm(2); G8, Er:YAG laser 150 mJ, 45 degrees non-contact, 1.55 J/cm(2); and G9, Er:YAG laser 70 mJ, 45 degrees non-contact, 0.72 J/cm(2). Bonding procedures were carried out and the micro-shear-bond strength (MSBS) test was performed. The adhesive surfaces were analyzed under SEM. Two-way ANOVA and multiple comparison tests revealed that MSBS was significantly influenced by the laser irradiation (p < 0.05). Mean values (MPa) of the MSBS test were: G1 (44.97 +/- 6.36), G2 (23.83 +/- 2.46), G3 (30.26 +/- 2.57), G4 (35.29 +/- 3.74), G5 (41.90 +/- 4.95), G6 (27.48 +/- 2.11), G7 (34.61 +/- 2.91), G8 (37.16 +/- 1.96), and G9 (41.74 +/- 1.60). It was concluded that the Er:YAG laser can constitute an alternative tool for dentin treatment before bonding procedures.

Fluoride uptake and acid resistance of enamel irradiated with Er : YAG laser

This study evaluated the resistance to demineralization and fluoride incorporation of enamel irradiated with Er:YAG. A total of 110 bovine teeth were selected and divided into eight groups: unlased, 37% phosphoric acid, and samples irradiated with the Er:YAG laser at several fluences (31.84 J/cm(2), 25.47 J/cm(2), 19.10 J/cm(2), 2.08 J/cm(2), 1.8 J/cm(2), and 0.9 J/cm(2)). The application of acidulated phosphate fluoride was performed after treatments. All samples were immersed in 2 ml of 2.0 M acetic-acetate acid solution at pH 4.5 for 8 h, and fluoride, calcium, and phosphorus ions dissolved were analyzed by atomic absorption spectrometry and spectrophotometry. The phosphoric acid and 31.84 J/cm(2) groups presented the lowest dissolution of calcium and phosphorus ions. Higher fluoride incorporation was observed on 1.8 J/cm(2) and 0.9 J/cm(2) groups. Based on these results, Er:YAG laser was able to decrease acid dissolution and increase fluoride uptake and can be a promissory alternative for preventive dentistry.