Effect of home bleaching agents on the microhardness of human enamel and dentin

In this study, the effects of home bleaching agents that contains carbamide peroxide (in different concentrations such as 10 and 15%) on the surface hardness of human enamel and dentine were evaluated. The buccal surfaces of 90 recently extracted human mandibular anterior teeth were used. The specimens in the dentine group were ground to expose of dentine surface. Then, samples in both enamel and dentine group were randomly divided into six main groups with 15 in each group. In the group 1 and 4, 15% carbamide peroxide was applied to the enamel and dentine surfaces and then the teeth were left in an incubator at 37°C and 100% humidity for 4 h first, then left 28 h after repeating the same procedures seven times. The teeth were treated with 10% carbamide peroxide in groups 2 and 5 and distilled water in groups 3 and 6 (control groups), using the same procedures. Vicker's microhardness of enamel and dentine were assessed on each tooth before and after each treatment period (4 and 28 h). The hardness of control group specimens was also obtained after 4 h in distilled water and then after 28 h. For statistical analysis one-way ANOVA and post-hoc Tukey tests were used. For both 10 and 15%, there were no statistically significant differences between the untreated control specimens and the specimens treated with the bleaching materials for enamel and dentine at any given measurement time (P > 0.05). Nevertheless, in vivo use of bleaching agents on tooth hard tissues requires further analysis.