In vitro assessment of laser efficiency for caries prevention in pits and fissures.

This study aimed to assess the in vitro efficacy of the lasers Er:YAG, Nd:YAG, and CO(2) operating in the low energy mode for caries prevention in pits and fissures. Forty-five caries-free enamel occlusal sections were randomly divided into three groups: G1 - Er:YAG (80 mJ/2 Hz); G2 - Nd:YAG Laser (1 W and 10 Hz); and G3 - CO(2) Laser (0.4 W and 20 Hz). After surface treatment, the samples were submitted to challenge with acid consisting of a 10-day immersion in demineralizing (6 h) and remineralizing solution (18 h). Next, enamel demineralization was quantitatively evaluated by subsurface microhardness test and polarized-light microscopy (PLM, mm(2)) and qualitatively assessed by scanning electron microscopy. The Wilcoxon test was used for comparison of each group with its own control. ANOVA (α = 5%) was employed for comparison among groups, and Fisher's LSD multiple comparison test was applied, to check the difference in means. Concerning the microhardness analyses, statistical difference between control, and experimental areas was only detected for the CO(2) group. Experimental values were higher than the controls. As for PLM analyses, smaller demineralized areas were measured for G2 (Nd:YAG) and G3 (CO(2)) compared with the control areas. In conclusion, the present findings suggest that the CO(2) laser should be selected in order to increase the enamel resistance to acid in pits and fissures.

Influence of the irradiation distance and the use of cooling to increase enamel-acid resistance with Er:YAG laser.

OBJECTIVES: The aim of this study was to assess the influence of irradiation distance and the use of cooling in the Er:YAG laser efficacy in preventing enamel demineralization. METHODS: 84 enamel blocks were randomly assigned to seven groups (n=12): G1: control group - no treatment, G2-G7: experimental groups treated with Er:YAG laser (80mJ/2Hz) at different irradiation distances with or without cooling: G2: 4mm/2mL; G3: 4mm/no cooling; G4: 8mm/2mL; G5: 8mm/no cooling; G6: 16mm/2mL; G7: 16mm/no cooling. The samples were submitted to an in vitro pH cycles for 14 days. Next, the specimens were sectioned in sections of 80-100microm in thickness and the demineralization patterns of prepared slices were assessed using a polarized light microscope. Three samples from each group were analyzed with scanning electronic microscopy. Analysis of variance and the Fisher test were performed for the statistical analysis of the data obtained from the caries-lesion-depth measurements (CLDM) (alpha=5%). RESULTS: The control group (CLDM=0.67mm) was statistically different from group 2 (CLDM=0.42mm), which presented a smaller lesion depth, and group 6 (0.91mm), which presented a greater lesion depth. The results of groups 3 (CLDM=0.74mm), 4 (CLDM=0.70mm), 5 (CLDM=0.67mm) and 7 (CLDM=0.89mm) presented statistical similarity. The scanning electronic microscopy analysis showed ablation areas in the samples from groups 4, 5, 6 and 7, and a slightly demineralized area in group 2. CONCLUSIONS: It was possible to conclude that Er:YAG laser was efficient in preventing enamel demineralization at a 4-mm irradiation distance using cooling.

Comparative study of physico-chemical properties of MTA-based and Portland cements.

The purpose of this investigation was to evaluate the physicochemical properties of gray and white structural and nonstructural Portland cement, gray and white ProRoot MTA and MTA BIO. The water/powder ratio, setting time, solubility and pH (hydrogen-ion potential) changes of the materials were evaluated. Tests followed specification #57 from the American National Standard Institute/American Dental Association (2000) for endodontic sealing materials and pH was determined by a digital pH meter. The test results were statistically analyzed by variance analyses for global comparison and by the complementary Tukey's test for pairwise comparisons (5%). Considering the water/powder ratio, no significant difference (p > 0.05) was observed among the cements. MTA BIO (33.10 +/- 2.30) had the lowest setting time (p < 0.05), gray ProRoot MTA (10.10 +/- 2.70) had the highest (p < 0.05). White nonstructural Portland cement (2.55 +/- 0.08) had the highest solubility (p < 0.05), while gray ProRoot MTA (1.03 +/- 0.12) had the lowest (p < 0.05), although all materials showed solubility values in compliance to ANSI/ADA. No difference (p > 0.05) was observed among materials when considering pH evaluation. The pH levels were highly alkaline immediately after immersion in solution, remaining stable throughout the test period. The authors conclude that the cements had similar water/powder proportions. MTA BIO had the shortest setting time and gray ProRoot MTA had the lowest solubility. All cements had similar behavior in the pH analysis.

Influence of cavity preparation with Er:YAG Laser on enamel adjacent to restorations submitted to cariogenic challenge in situ: a polarized light microscopic analysis.

BACKGROUND AND OBJECTIVES: Er:YAG laser has been used for caries removal and cavity preparation, using ablative parameters. Its effect on the margins of restorations submitted to cariogenic challenge has not yet been sufficiently investigated. The aim of this study was to assess the enamel adjacent to restored Er:YAG laser-prepared cavities submitted to cariogenic challenge in situ, under polarized light microscopy. STUDY DESIGN/MATERIALS AND METHODS: Ninety-one enamel slabs were randomly assigned to seven groups (n = 13): I, II, III-Er:YAG laser with 250 mJ, 62.5 J/cm2, combined with 2, 3, and 4 Hz, respectively; IV, V, VI-Er:YAG laser with 350 mJ, 87.5 J/cm(2), combined with 2, 3, and 4 Hz, respectively; VII-High-speed handpiece (control). Cavities were restored and the restorations were polished. The slabs were fixed to intra-oral appliances, worn by 13 volunteers for 14 days. Sucrose solution was applied to each slab six times per day. Samples were removed, cleaned, sectioned and ground to polarized light microscopic analysis. Demineralized area and inhibition zone width were quantitatively assessed. Presence or absence of cracks was also analyzed. Scores for demineralization and inhibition zone were determined. RESULTS: No difference was found among the groups with regard to demineralized area, inhibition zone width, presence or absence of cracks, and demineralization score. Inhibition zone score showed difference among the groups. There was a correlation between the quantitative measures and the scores. CONCLUSION: Er:YAG laser was similar to high-speed handpiece, with regard to alterations in enamel adjacent to restorations submitted to cariogenic challenge in situ. The inhibition zone score might suggest less demineralization at the restoration margin of the irradiated substrates. Correlation between the quantitative measures and scores indicates that score was, in this case, a suitable complementary method for assessment of caries lesion around restorations, under polarized light microscopy.