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 (80 mJ/2 Hz) at different irradiation distances with or without cooling: G2: 4 mm/2 mL; G3: 4 mm/no cooling; G4: 8 mm/2 mL; G5: 8 mm/no cooling; G6: 16 mm/2 mL; G7: 16 mm/no cooling. The samples were submitted to an in vitro pH cycles for 14 days. Next, the specimens were sectioned in sections of 80-100 mu m 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 = 0.67 mm) was statistically different from group 2 (CLDM = 0.42 mm), which presented a smaller lesion depth, and group 6 (0.91 mm), which presented a greater lesion depth. The results of groups 3 (CLDM = 0.74 mm), 4 (CLDM = 0.70 mm), 5 (CLDM = 0.67 mm) and 7 (CLDM = 0.89 mm) 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. (C) 2010 Elsevier Ltd. All rights reserved.

Shear Bond Strength of A Sealant to Contaminated-Enamel Surface: Influence of Erbium : Yttrium-Aluminum-Garnet Laser Pretreatment

Salivary contamination is one of the factors that can disturb the sealing process and interfere in the longevity of pit and fissure sealants. Erbium : yttrium-aluminum-garnet (Er : YAG) laser could influence the bond strength of enamel and increase the acid resistance. To evaluate the influence of Er : YAG laser on the shear bond strength of a sealant to a salivary contaminated enamel surface. Twenty-four third molars had the roots sectioned 2 mm coronal to the cementoenamel junction. The crowns were mesiodistally sectioned providing 48 halves that were embedded in polyester resin. Enamel was flattened and a 2-mm diameter bonding area was demarcated. Specimens were randomly assigned to two groups according to the superficial pretreatment-37% phosphoric acid (A) and Er : YAG laser (80 mJ/2 Hz) + phosphoric acid (L), which were subdivided into two groups (N = 12), without salivary contamination (C) and with salivary contamination (SC). To contaminate the specimens, 0.25 mL of human fresh saliva was applied for 20 seconds and then dried. Fluroshield sealant was applied in all specimens. After storage, shear bond strength of samples were tested in a universal testing machine. Means in MPa were: AC-14.61 (+/- 2.52); ASC-6.66 (+/- 2.34); LC-11.91 (+/- 1.34); and LSC-2.22 (+/- 0.66). Statistical analysis revealed that surfaces without salivary contamination and with acid treatment had the highest mean (p < 0.05). The group with salivary contamination treated by Er : YAG laser followed by phosphoric acid application presented the lowest bond values (p < 0.05). The phosphoric acid etching under dry condition yielded better bonding performance. Er : YAG laser was not able to increase the effectiveness of conventional acid etching of enamel in the bond of sealants in both dry and wet conditions. Under the conditions of this study, the conventional etching protocol (phosphoric acid without salivary contamination) is still preferable to laser-conditioning enamel surface prior to sealant application.

Shear Bond Strength and Ultrastructural Interface Analysis of Different Adhesive Systems to Bleached Dentin

Background: It remains unclear as to whether or not dental bleaching affects the bond strength of dentin/resin restoration. Purpose: To evaluated the bond strength of adhesive systems to dentin submitted to bleaching with 38% hydrogen peroxide (HP) activated by LED-laser and to assess the adhesive/dentin interfaces by means of SEM. Study design: Sixty fragments of dentin (25 mm(2)) were included and divided into two groups: bleached and unbleached. HP was applied for 20 s and photoactivated for 45 s. Groups were subdivided according to the adhesive systems (n = 10): (1) two-steps conventional system (Adper Single Bond), (2) two-steps self-etching system (Clearfil standard error (SE) Bond), and (3) one-step self-etching system (Prompt L-Pop). The specimens received the Z250 resin and, after 24 h, were submitted to the bond strength test. Additional 30 dentin fragments (n = 5) received the same surface treatments and were prepared for SEM. Data were analyzed by ANOVA and Tukey`s test (alpha = 0.05). Results: There was significant strength reduction in bleached group when compared to unbleached group (P < 0.05). Higher bond strength was observed for Prompt. Single Bond and Clearfil presented the smallest values when used in bleached dentin. SEM analysis of the unbleached specimens revealed long tags and uniform hybrid layer for all adhesives. In bleached dentin, Single Bond provided open tubules and with few tags, Clearfil determined the absence of tags and hybrid layer, and Prompt promoted a regular hybrid layer with some tags. Conclusions: Prompt promoted higher shear bond strength, regardless of the bleaching treatment and allowed the formation of a regular and fine hybrid layer with less deep tags, when compared to Single Bond and Clearfil. Microsc. Res. Tech. 74:244-250, 2011. (C) 2010 Wiley-Liss, Inc.