Effect of 10% sodium ascorbate and 10% alpha-tocopherol in different formulations on the shear bond strength of enamel and dentin submitted to a home-use bleaching treatment.

This in vitro study assessed the shear bond strength of human enamel and dentin submitted to a bleaching treatment with 10% carbamide peroxide and treatment with antioxidant agents containing 10% alpha-tocopherol and 10% sodium ascorbate formulated in solution and gel. Sixty human dental enamel slabs (E) and 60 human dental dentin slabs (D) were randomly divided into six groups (n = 10). Groups E1 and D1 were negative control groups and the bleaching agent was not applied. The bleaching agent was applied daily for two-hours on the dental slabs of all the other groups and, during the remaining 22 hours, the specimens were stored in an artificial saliva solution for a total of 14 days. Groups E2 and D2 were positive control groups and they only received application of the bleaching agents. Antioxidant agents were applied in Groups E3 and D3 (10% sodium ascorbate solution), E4 and D4 (10% alpha-tocopherol solution), E5 and D5 (10% sodium ascorbate gel) and E6 and D6 (10% alpha-tocopherol gel) for two hours. Cylinders were made with microhybrid resin composite and a total-etch adhesive system for shear bond strength tests. These tests were performed in a universal testing machine at a speed of 0.5 mm/minute to obtain the values in MPa. ANOVA (p > 0.05) showed no significant differences among groups E4, E5, E6 and E1. However, groups E3, E5 and E6 presented statistically similar values to group E2. The Kruskal-Wallis test showed no significant differences among D1 and all the other experimental groups; the same values occurred with D2, which did not differ from the experimental groups. Antioxidant treatment with 10% alpha-tocopherol solution was the only effective agent to revert the oxidizing effects of the bleaching treatment on enamel.