Concentration-dependent effect of bleaching agents on microhardness and roughness of enamel and dentin

To evaluate the microhardness and surface roughness of enamel and root dentin bleached with 10%, 15% and 22% carbamide peroxide agents.52 slabs of enamel and root dentin (6 x 3 x 2 mm) were cut from bovine incisors, ground flat and polished. According to a randomized complete block design, enamel and root dentin slabs (n = 13) were independently allocated to be bleached with one of the following carbamide peroxide-containing agents (CP): 10% (Rembrandt Bleaching Gel Plus), 15% (Rembrandt Xtra Comfort), or 22% (Rembrandt Xtra Comfort Ultra Strength). The control groups were mock-treated with artificial saliva. The bleaching procedures consisted of daily application of the agents on dental substrate surfaces for 2 hours, followed by immersion in artificial saliva for 22 hours over 21 days. Knoop microhardness and surface roughness were measured initially, on sound dental tissues, and at the postbleaching phase.In enamel, microhardness attained after bleaching with 10% CP and 15% CP were similar and significantly lower than that observed for the control group. Specimens bleached with CP 22% did not differ from any of the other groups tested. In root dentin, microhardness changes were indistinguishable. ANOVA showed no significant difference among treatments with respect to surface roughness.