Effect of different concentrations of carbamide peroxide on microhardness of dental ceramics.

PURPOSE: To evaluate the effect of 10% and 16% carbamide peroxide bleaching agents on microhardness of dental ceramics after different periods of bleaching treatment. METHODS: 15 specimens with 5 x 3 x 1 mm3 were created with four dental ceramics following manufacturers' instructions: IPS Classic (Ivoclar-Vivadent); IPS d.Sign (Ivoclar-Vivadent); EX3 (Noritake); VMK-95 (Vita). A microhardness tester with a Knoop diamond with a 100 g load was used to evaluate the baseline microhardness values of all ceramics. Afterwards, the specimens were submitted to 6-hour daily bleaching treatments with 10% or 16% carbamide peroxide (Whiteness Perfect-FGM) for 21 days, while control groups from each ceramic system were maintained in artificial saliva. The microhardness of all groups was evaluated at 18, 42, 84, and 126 hours of bleaching treatment. The mean value of five indentations performed at each specimen in each time was obtained and all data were submitted to two-way repeated measures ANOVA and Tukey's post-hoc test (alpha = 0.05). RESULTS: No significant differences in ceramic microhardness were observed among either bleaching intervals or bleaching treatments. Ceramic restorations are not affected by carbamide peroxide 10% or 16% gel during bleaching treatment.