Influence of etching time on bond strength in dentin irradiated with erbium lasers.

The purpose of this in vitro study was to evaluate the effect of etching time on the tensile bond strength (TBS) of a conventional adhesive bonded to dentin previously irradiated with erbium:yttrium-aluminum-garnet (Er:YAG) and erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) lasers. Buccal and lingual surfaces of 45 third molars were flattened until the dentin was exposed and randomly assigned to three groups (n = 30) according to the dentin treatment: control (not irradiated), irradiated with Er:YAG (1 W; 250 mJ; 4 Hz; 80.6 J/cm(2)) laser or Er,Cr:YSGG (4 W; 200 mJ; 20 Hz; 71.4 J/cm(2)) laser, and into three subgroups (n = 10) according to acid etching time (15 s, 30 s or 60 s) for each experimental group. After acid etching, the adhesive was applied, followed by the construction of an inverted cone of composite resin. The samples were immersed in distilled water (37 degrees C for 24 h) and subjected to TBS test [50 kilogram-force (kgf), 0.5 mm/min]. Data were analyzed by analysis of variance (ANOVA) and Tukey statistical tests (P < or = 0.05). Control group samples presented significant higher TBS values than those of all lased groups. Both irradiated groups exhibited similar TBS values. Samples subjected to the different etching times in each experimental group presented similar TBS. Based on the conditions of this in vitro study we concluded that Er:YAG and Er,Cr:YSGG laser irradiation of the dentin weakens the bond strength of the adhesive. Moreover, increased etching time is not able to modify the bonding strength of the adhesive to irradiated dentin.

Laser phototherapy as topical prophylaxis against head and neck cancer radiotherapy-induced oral mucositis: comparison between low and high/low power lasers.

BACKGROUND AND OBJECTIVE: Oral mucositis is a dose-limiting and painful side effect of radiotherapy (RT) and/or chemotherapy in cancer patients. The purpose of the present study was to analyze the effect of different protocols of laser phototherapy (LPT) on the grade of mucositis and degree of pain in patients under RT. PATIENTS AND METHODS: Thirty-nine patients were divided into three groups: G1, where the irradiations were done three times a week using low power laser; G2, where combined high and low power lasers were used three time a week; and G3, where patients received low power laser irradiation once a week. The low power LPT was done using an InGaAlP laser (660 nm/40 mW/6 J cm(-2)/0.24 J per point). In the combined protocol, the high power LPT was done using a GaAlAs laser (808 nm, 1 W/cm(2)). Oral mucositis was assessed at each LPT session in accordance to the oral-mucositis scale of the National Institute of the Cancer-Common Toxicity criteria (NIC-CTC). The patient self-assessed pain was measured by means of the visual analogue scale. RESULTS: All protocols of LPT led to the maintenance of oral mucositis scores in the same levels until the last RT session. Moreover, LPT three times a week also maintained the pain levels. However, the patients submitted to the once a week LPT had significant pain increase; and the association of low/high LPT led to increased healing time. CONCLUSIONS: These findings are desired when dealing with oncologic patients under RT avoiding unplanned radiation treatment breaks and additional hospital costs.

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.

Cultured epithelial cells response to phototherapy with low intensity laser.

BACKGROUND AND OBJECTIVES: Little is known about the intracellular response of epithelial cells to phototherapy. The aim of this in vitro study was to analyze the effect of phototherapy with low-energy lasers with different wavelengths and powers on cultured epithelial cell growth under different nutritional conditions. STUDY DESIGN/MATERIALS AND METHODS: Epithelial cell cultures (Vero cell line) grown in nutritional deficit in culture medium supplemented with 2% fetal bovine serum (FBS) were irradiated with low-energy laser from one to three times with a GaAlAs laser (660 nm) and InGaAlP (780 nm), 40 and 70 mW, respectively, with 3 or 5 J/cm2. Cell growth was indirectly assessed by measuring the cell mitochondrial activity. RESULTS: Nonirradiated cell cultures grown in nutritional regular medium supplemented with 10% FBS produced higher cell growth than all cultures grown in nutritional deficit irradiated or not. The overall cell growth of cultures grown under nutritionally deficit conditions was significantly improved especially when irradiated with 780 nm for three times. CONCLUSIONS: Phototherapy with the laser parameters tested increases epithelial cell growth rate for cells stressed by growth under nutritionally deficient states. This cell growth improvement is directly proportional to the number of irradiations; however, was not enough to reach the full cell growth potential rate of Vero epithelial cell line observed when growing under nutritional regular condition.

Caries inhibition around composite restorations by pulsed carbon dioxide laser application.

This in vitro study aimed to evaluate whether laser irradiation of cavity margins reduces enamel demineralization around composite restoration. Enamel cavities were prepared in 33 human enamel slabs, which were randomly divided into three groups. One group was kept as a control, and the cavosurface margin of the cavities of the other groups were irradiated, using a CO(2) laser (lambda = 10.6 microm), at 8 J.cm(-2) or 16 J.cm(-2). The cavities were restored with a resin-based composite, according to the manufacturer's specifications. Before restoration, scanning electron microscopy was performed on one specimen of each group. The remaining slabs were submitted to thermal and pH-cycling models. Enamel mineral loss, at 50 and 100 microm from the restoration margin, was assessed by cross-sectional microhardness analyses. Fusion and melting were observed in the irradiated groups. Mineral loss at 50 microm from the restoration margin was significantly inhibited in the irradiated groups compared to the control group, but at 100 microm from the restoration margin, mineral loss at only the highest laser energy density differed statistically from the control group. The difference between the irradiated groups was not statistically significant at either 50 or 100 microm from the restoration margin. In conclusion, irradiation of the cavosurface margin of cavities, using a pulsed CO(2) laser, is able to inhibit enamel demineralization around composite restorations, and an energy density of 16 J.cm(-2) is efficient, even at 100 microm from the cavity margin.

Intrapulpal temperature during preparation with the Er:YAG laser: an in vitro study.

OBJECTIVE: This investigation evaluated the variation of the intrapulpal temperature when dentine was irradiated by the Er:YAG laser. BACKGROUND DATA: The effect of preparation with the Er:YAG laser on the intrapulpal temperature is probably the biggest problem in using the laser for preparation of dental hard tissue. MATERIALS AND METHODS: Seventy-two bovine incisors were studied that had the enamel and dentine of the buccal surface polished to a thickness of 2.0 mm. The teeth were divided into three groups, according to the repetition rate used (Group I = 2 Hz, Group II = 4 Hz, and Group III = 6 Hz), and irradiated, with or without water cooling, using 250, 300, and 350 mJ of energy per pulse. Thermocouples were introduced inside the pulp chamber through the palatine opening of the samples and fixed to the vestibular wall of the pulp chamber using a thermal paste. RESULTS: It was verified that there was a decrease of the intrapulpal temperature for all of the parameters in the Group I irradiated with water cooling and for the parameters of 350 mJ/4 Hz with water cooling. The other irradiations showed an increase of the intrapulpal temperature, varying from 0.03 degrees to 2.5 degrees C. CONCLUSION: We conclude that the use of the Er:YAG laser promoted acceptable temperature increases inside the pulp chamber. However, we do not recommend this procedure without water cooling because macroscopic observations of the dentine irradiated without water cooling showed dark lesions, suggesting carbonization of this tissue.

Effect of low-power laser irradiation on protein synthesis and ultrastructure of human gingival fibroblasts.

BACKGROUND AND OBJECTIVES: Low-power lasers improve wound healing. Cell proliferation and protein secretion are important steps of this process. The aim of this study was to analyze both protein synthesis and ultrastructural morphology of human gingival fibroblasts irradiated by a low-power laser. STUDY DESIGN/MATERIALS AND METHODS: The cell line FMM1 was grown in nutritional deficit. Laser irradiation was carried out with a gallium-aluminum-arsenate (Ga-Al-As) diode laser (904 nm, 120 mW, energy density of 3 J/cm(2)). The protein synthesis analysis and ultrastructural morphology of control (non-irradiated) and irradiated cultures were obtained. RESULTS: There were changes in the structure of cytoplasm organelles of treated cells. The procollagen was not altered by the laser irradiation; however, there were a significant reduction of the amount of protein in the DMEM conditioned by irradiated cells. CONCLUSIONS: Low-power laser irradiation causes ultrastructural changes in cultured fibroblasts. We suggest that these alterations may lead to disturbances in the collagen metabolism.

Adhesion and growth of cultured human gingival fibroblasts on periodontally involved root surfaces treated by Er:YAG laser.

BACKGROUND: The application of Er:YAG laser irradiation, approved in 1997 to be used on dental hard tissues, has been investigated for periodontal therapy. The aim of this study was to analyze the biocompatibility of root surfaces treated by Er:YAG laser. METHODS: Adhesion and growth of cultured human gingival fibroblasts on root surfaces treated by either irradiation with Er:YAG laser or curet were compared. Thirty single-rooted teeth extracted because of periodontal disease were used. Calculus deposits on all experimental surfaces were removed, and the teeth were divided into three groups according to the applied treatment: group A, root planing with Gracey curet no. 3/4; group B, two irradiations with laser (60 mJ/pulse, 10 Hz; 10" each with 10-second interval, 3 J/cm2); group C, two irradiations with laser (100 mJ/pulse, 10 Hz; 10" each with 10-second interval, 5 J/cm2). Fragments (5 mm x 6 mm) were obtained from the experimental surfaces. Then, 1 x 10(3) cells were seeded on the top of each fragment. One, 2, and 3 days after seeding the specimens were prepared for scanning electron microscopy analysis, and the cells on the electronmicrographs were counted. The data obtained in triplicate were statistically compared by the Kruskall-Wallis test complemented by the Dunn test (P < or = 0.05). RESULTS: Human gingival fibroblasts adhered to and grew on all treated surfaces. Group B presented a significantly higher cell count than did the other two groups at days 1 and 2. Three days after seeding the cultured fibroblasts of groups A and B reached total confluence. The cell count of group B was significantly higher than that of group C. CONCLUSION: The surfaces treated with 60 mJ/pulse Er:YAG laser irradiation promoted faster adhesion and growth than surfaces treated with either root planing or 100 mJ/pulse Er:YAG laser irradiation.

Er:YAG laser effects on enamel occlusal fissures: an in vitro study.

This study evaluated by scanning electron microscopy (SEM) the morphological changes in occlusal fissure enamel, of permanent models, irradiated by Er:YAG laser using contact and noncontact fiberoptics in vitro. Previous studies have demonstrated the efficacy of Er:YAG laser for dental hard tissue removal and cavity preparation. The treatment of occlusal fissures in noncarious permanent human molars (n = 9) was carried out with Er:YAG laser (KEY Laser II) using handpiece no. 2051, noncontact, focused (12 mm), water spray-cooled, pulse energy 200 mJ, and frequency 2 Hz (group 1), and handpiece no. 2055 with a quartz fiberoptic 50/10, in contact, air cooled, pulse energy setting of 350 mJ and frequency 2 Hz (group 2) and 400 mJ/2 Hz (group 3). The specimens were sectioned, dehydrated in a graded series of aqueous ethanol, dried, and sputtering with gold. Morphological change analysis on occlusal fissures was performed by SEM. Group 1 showed removal of fissure debris and predominantly enamel etching-like patterns, and groups 2 and 3 showed irregular edges, melting, and recrystallization of fissure enamel, with a lava-like structure and bubble-like voids. The results of this in vitro study suggest that the irradiation of fissures by Er:YAG laser using a fiberoptics (contact and air cooled) produced melting and recrystallization of fissures enamel. Further studies are required with different energy parameters and water cooling to evaluate the thermal effects on teeth.