Efficacy of In-office Bleaching on Microhardness of Permanent Teeth with Antioxidant Re-hardening

Abstract

Background: Bleaching procedures affect surface enamel structure and decrease its bonding ability to resin composite restorative materials. The application of re-hardening materials to bleached enamel surfaces may prevent this decrease in micro-hardness. Objective: This in-vitro study aims to evaluate the surface micro hardness of human teeth enamel subjected to bleaching with Zoom Advanced Power 2 AP (Phillips, USA), and Opalescence Boost (Ultradent, USA) and compare the re-hardening effects of 10\% Sodium Ascorbate, 2\% acidulated phosphate fluoride gel, and a 5\% Potassium nitrate 0.22\% Sodium Fluoride + Calcium Nitrate gel. Methods: Ninety human third molar teeth were used. The specimens were randomly assigned to 5 groups. After the bleaching procedure, the specimens were treated with APF, Sodium Ascorbate or Relief gel as re-hardening agents with 30 teeth in each group. Enamel micro-hardness was measured with Vickers Micro-hardness Tester. The data were evaluated with Kolmogorov-Simirnov, one-way ANOVA, Dunnett's test, post-hoc Tukey and T-tests. Results: Statistical analysis revealed no significant differences among initial enamel groups' micro-hardness values (P>.05), however, significant differences occurred between initial and after bleaching treatment group value for G3 (P