The effect of home bleaching carbamide peroxide concentration on the microhardness of dental composite resins

Bleaching is a conservative treatment for discolored teeth, but the effect of this treatment on newer, silorane-based composite resins is unclear. This study evaluated the effect of at-home bleaching on the microhardness of methacrylate- and silorane-based composites. Forty blocks each of a methacrylate-based composite and a silorane-based composite were prepared. The 80 specimens were tested in 8 groups (n = 10): 2 composites, each exposed to 3 different carbamide peroxide concentrations (10%, 16%, or 22%) as well as distilled water (control). The surface of the test specimens was covered daily with the bleaching gel at room temperature for the time period recommended by the manufacturer for each carbamide peroxide concentration. A Vickers hardness testing machine was used with a 100-g load for 20 seconds to register specimen microhardness prior to and after 2 weeks of bleaching. The load was applied at 3 points, and the mean microhardness was calculated. Repeated-measures analysis of variance, paired t test, and Tukey test were used to analyze the data. All bleaching concentrations significantly decreased the microhardness of the methacrylate-based composite resin groups, while microhardness was significantly increased in the silorane-based composite resin groups. There was no evident difference in effects among the different gel concentrations (P > 0.05).