Methods: 12 disc shaped specimens (A3 shade) of each composite (Filtek P90, Filtek Z350XT Enamel, Filtek Z250 (3M-ESPE, St Paul MN USA)) were fabricated according to the manufacturer's instructions using a stainless steel mold and were polished with SiC paper. Then the specimens were stored in 100% humidity for 24 hours. The samples of each type of composites were randomly divided into two groups (n=6). [Control: 2 weeks storage in distilled water at room temperature, experimental: exposure to Opalescence Boost (Ultradent, S Jordan UT, USA)]. Vickers microhardness and the color of samples were evaluated before and after each treatment. A spectrophotometric analysis was used to measure the following color parameters in the CIE L*a*b* color space: deltaa*, deltab*, deltaL*, deltaH, deltaC, and deltaE. Data were analyzed using repeated measure ANOVA.
Results: The baseline microhardness of Filtek P90 was significantly lower than the two other composites (P=0.001), but there was not any difference between Z250 and Z350XT (P=0.293). Opalescence Boost significantly decreased the microhardness of Z250 and Z350XT (P<0.001), but no significant change was observed in either the experimental or control groups of P90 (P>0.05). After bleaching, deltaE was evaluated 3.12 (1.97), 3.31 (1.84) and 3.7 (2.11) for P90, Z250, and Z350 respectively with no significant difference.
Conclusions: Using 40% H2O2 decreased the microhardness value of metacrylate-based composites but not the silorane-based composite. Although there was not any difference between the deltaE of composites, the deltaE of P90 remained in the range of clinical acceptance (deltaE<3.3).