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This in vitro study evaluated the effect of sodium bicarbonate and sodium ascorbate on the microtensile bond strength of an etch-and-rinse system to bleached bovine enamel. Sixty bovine enamel blocks (4x4 mm) were flattened and randomly allocated into 5 groups: G1 (negative control): without treatment; G2 (positive control): bleached with 35% hydrogen peroxide (HP); G3: bleached and stored for 7 days in artificial saliva before restorative procedures; G4: bleached and treated with 10% sodium bicarbonate solution for 5 min; G5: bleached and treated with 10% sodium ascorbate hydrogel for 15 min. HP gel was applied twice (20 min each, except in G1) and the adhesive restorations were performed. After 24 h, the specimens were sectioned into sticks and submitted to microtensile bond strength testing with a crosshead speed of 0.5 mm/min (n=12). As a complementary visual observation, the enamel surfaces of the G1 and G2 specimens were evaluated with scanning electron microscopy. Data were analyzed by one-way ANOVA (p<0.05). The means (standard deviation) were: G1: 24.22±7.74; G2: 18.29±5.88; G3: 40.88±7.95; G4: 19.95±5.67 and G5: 24.43±6.43. Adhesive failures were predominant in all groups. The comparison between the treatments indicates that waiting 7 days after bleaching is still the most effective approach. When this waiting period is not possible, application of sodium ascorbate or sodium bicarbonate seems to be a good alternative. Therefore, the practicality of obtaining sodium bicarbonate in the bleaching kits and its higher stability enables its clinical use.

Unlabelled: Development of new materials for tooth bleaching justifies the need for studies to evaluate the changes in the enamel surface caused by different bleaching protocols., Objective: The aim of this study was to evaluate the bovine dental enamel wear in function of different bleaching gel protocols, acid etching and pH variation., Material and Methods: Sixty fragments of bovine teeth were cut, obtaining a control and test areas. In the test area, one half received etching followed by a bleaching gel application, and the other half, only the bleaching gel. The fragments were randomly divided into six groups (n=10), each one received one bleaching session with five hydrogen peroxide gel applications of 8 min, activated with hybrid light, diode laser/blue LED (HL) or diode laser/violet LED (VHL) (experimental): Control (C); 35% Total Blanc Office (TBO35HL); 35% Lase Peroxide Sensy (LPS35HL); 25% Lase Peroxide Sensy II (LPS25HL); 15% Lase Peroxide Lite (LPL15HL); and 10% hydrogen peroxide (experimental) (EXP10VHL). pH values were determined by a pHmeter at the initial and final time periods. Specimens were stored, subjected to simulated brushing cycles, and the superficial wear was determined (μm). ANOVA and Tukey´s tests were applied (α=0.05)., Results: The pH showed a slight decrease, except for Group LPL15HL. Group LPS25HL showed the highest degree of wear, with and without etching., Conclusion: There was a decrease from the initial to the final pH. Different bleaching gels were able to increase the surface wear values after simulated brushing. Acid etching before bleaching increased surface wear values in all groups.