Effects of Carbamide Peroxide Bleaching Agent on Color and Translucency Changes of Three Composite Resin Types with or without Bonding Agent

  The bleaching agents can lead to color and translucency changes in composite resins. Due to the increasing use of nanocomposites and silorane-based composites, this study aimed to examine the color and translucency changes of restorations after applying the bleaching agents. In this experimental-laboratory study, 132 composite discs were divided into three groups based on the composite type, including the microhybrid composite Z250, nanohybrid composite Z350, and silorane-based composite P90. After acid etching on half of the samples in each group, they were covered with resin bonding agent. Then the color and translucency evaluation was performed by reflectance spectrophotometer using CIELAB system(USA, II-Xrite). Each composite subgroup was divided into two new subgroups, namely 20% carbamide peroxide bleaching agent and control groups. Final color and translucency changes were calculated and assessed after applying bleaching agent. The statistical analysis was carried out using the one-way analysis of variance, Tukey's Honest Significant Difference test, and t-test. The effects of composite and bleaching agent types, as well as bonding agent, on the samples’ surface were statistically significant (P<0.001). The color changes in the microhybrid composite were higher than those of nanohybrid and silorane-based composites (P<0.001). Moreover, the color changes in 20% carbamide peroxide bleaching group were higher than that of the control group (∆E>3.3; P<0.001). The results of translucency changes were consistent with the findings of color change measurements. According to the results of the present study, most of the color changes in the microhybrid composite appeared after applying 20% carbamide peroxide bleaching agent. The rebound samples were less affected by the bleaching agents. The least color and translucency changes were associated with nanohybrid composites