The effect of bleaching on microhardness of silorane-based composite resins

Bleaching treatments may negatively affect the surface quality of composite restorations existing in the mouth. This study sought to assess the effect of 16% and 35% carbamide peroxide on microhardness of silorane-based versus two methacrylate-based composite resins. A total of 54 discs were fabricated from FiltekP90 (P90), FiltekZ350XT(Z350) Enamel and Filtek Z250(Z250) (n=18). Each group of composite specimens was randomly divided into 3 subgroups (n=6). The control subgroup was stored in distilled water for 2 weeks. Subgroup 2 specimens were bleached 4hours a day with 16% carbamide peroxide (Home bleaching) for 14 days. The 3rd subgroup specimens were subjected to 35% carbamide peroxide (Office bleaching) applied once for 40 minutes. Microhardness of specimens was measured before and after bleaching by using Vickers hardness testing machine. Data were analyzed by using Repeated Measures ANOVA. Baseline microhardness of P90 was lower than that of the other two composite resins (p=0.001). Bleaching decreased the microhardness of Z250 and Z350 compared to the control group (p<0.001). However, in P90, only the office bleaching material caused a reduction in microhardness (p=0.009). The effect of home and office bleaching on microhardness of P90 was different (p=0.015). Bleaching treatments significantly decreased the microhardness of Z250 and Z350 composite resins but this reduction in P90 was not statistically significant after home bleaching.