Introdouction:Bleaching has become a common treatment for improving the appearance of natural teeth. However, the need to protect dental restorations from bleaching agent exposure is inevitable, as these agents may change the color of restorative materials by oxidation. Filtek P90 composite resin has recently been introduced with the aim of decreasing polymerization shrinkage. The purpose of this study was to compare the color changes of silorane-and methacrylate-based resin composites after exposure to various carbamide peroxide regimens. Materials and methods:Sixty-four disk-shaped specimens (10 × 2 mm) of a microhybrid composite, Z250, and a siloranebased composite, P90, were prepared and divided into four subgroups (n = 8). An unbleached group was used as a control, while the remaining specimens in the three subgroups were bleached with 10%, 16%, and 22% carbamide peroxide for 14 days. The color was measured with a spectrophotometer using Commission International de I'Eclairage L*, a*, and b* color scale. The data were analyzed using ANOVA, the t-test, and Tukey's HSD test. Results:Color differences between bleaching and baseline values (ΔE) were <3.3 for all the groups. Z250 and P90 resin composites showed color changes after bleaching with 10%, 16%, and 22% carbamide peroxide, but the changes were insignificant (Z250: p = 0.323, P90: p = 0.136). Conclusion:The color changes were not clinically evident in the sample groups. For both the Z250 and P90 specimens, no statistically significant differences in color were noted