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To evaluate the effect of a 10% carbamide peroxide-containing bleaching agent on brushing abrasion of esthetic restorative materials.Using a randomized complete block design, 150 specimens (n = 15) measuring 3 x 3 x 2 mm were fabricated into acrylic resin cylinders, using one of the restorative materials: a microfilled resin composite (Al), a hybrid resin composite (Ch), a flowable resin composite (Wa), a resin-modified glass-ionomer cement (Fj) and a polyacid-modified resin composite (Dy). The bleaching agent or artificial saliva (control) was applied for 2 hours/day. After that, 120 brushing strokes were simulated automatically and the samples were kept in artificial saliva. Such bleaching/brushing cycle was performed daily for 21 days. Wear depth was assessed using profilometry.Bleaching did not show significant effect on wear depth. There was a significant difference among the restorative materials. Tukey's test showed that (Al = Ch)(Wa)(Fj) and that Dy was only different from Fj.

To evaluate in vitro the susceptibility of caries-like lesion formation on enamel and root dentin that had been bleached with carbamide peroxide agents.150 slabs of bovine enamel and root dentin were ground flat and polished. According to a randomized complete block design, the specimens were then allocated to be bleached with agents (Rembrandt) containing 12% [CP12], 16% [CP16], 22% [CP22] or 30% [CP30] of carbamide peroxide over 21 days. The control group remained unbleached. Afterwards, all specimens were randomly distributed between two subgroups (n= 15): one was subjected to alternating demineralizing and remineralizing solutions to induce caries-like lesions and the other was not. Enamel specimens were cycled four times in demineralizing (pH 5.0) and remineralizing solutions (pH 7.0), while root dentin specimens were cycled twice. Microhardness measurements were carried out at the post-bleaching and at the post-caries lesion formation phases.In the post-bleaching condition, microhardness values for both enamel and root dentin were dependent on the bleaching agent used. At the post-caries formation stage, there was a significant interaction between the bleaching treatment and substrate condition (carious or noncarious) for enamel and root dentin. Regardless of the bleaching agent, carious enamel and root dentin presented significantly lower microhardness values as compared to the noncarious counterparts. For carious enamel, those specimens exposed to CP16 exhibited higher microhardness values than the subset group formed by CP22, CP30 and unbleached samples. Both subsets did not differ from CP12. For carious root dentin, no difference was observed among the microhardness values attained as a result of the different bleaching treatments.

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.