Effects of 15% Carbamide Peroxide and 40% Hydrogen Peroxide on the Microhardness and Color Change of Composite Resins

Objective: The aim of this study was to determine the effects of 40% hydrogen per- oxide and 15% carbamide peroxide on microhardness and color change of a silorane- based composite resin in comparison with two methacrylate-based composites. Materials and Methods: Fifty-four disc-shaped specimens (A3 shade) were fabricat- ed of Filtek P90 (P90), Filtek Z350XT Enamel (Z350) and Filtek Z250 (Z250) (3M- ESPE) (n=18). The samples of each composite were randomly divided into three subgroups of 6. The control subgroups were immersed in distilled water; the test groups were exposed to Opalescence Boost (OB) once; and Opalescence PF (OP) (Ul- tradent) for two weeks. Vickers microhardness testing and a spectrophotometric anal- ysis of the color of samples were performed before and after each intervention. Results: The baseline microhardness of P90 was significantly lower than that of the other two composites (P=0.001), but no difference was found between Z250 and Z350 in this respect (P=0.293). Bleaching treatments significantly decreased the microhard- ness of Z250 and Z350 (P< 0.001), but no change was observed in P90 test and con- trol subgroups (P> 0.05). No significant difference was detected between the two types of bleaching (P>0.05). After bleaching with OB, E value was measured to be 3.12(1.97), 3.31(1.84) and 3.7(2.11) for P90, Z250 and Z350, respectively. These val- ues were 5.98(2.42), 4.66(2.85) and 4.90(2.78) after bleaching with OP with no signif- icant difference. Conclusion: Bleaching decreased the microhardness of methacrylate-based but not silorane-based composites. Although no significant differences were found in E of composites, E of all groups did not remain in the clinically acceptable range after bleaching except for P90 after bleaching with 40% H2O2 ( E < 3.3).