PMC:2854328 / 5751-6942 JSONTXT

Two commercially available resin composites, Durafil VS (Heraeus Kulzer, Wehrheim, Germany) and TPH3 (Dentsply Caulk, Milford, USA), were used in this study. Durafil VS (DF) is a microfilled composite composed of 40% volume silicon dioxide fillers and BisGMA matrix, while TPH3 is a microhybrid composite composed of 58% volume barium-alumino-boro-silicate, fluoro-boro-silicate fillers, and a matrix of BisGMA and TEGDMA. Twenty-four specimens, 15 mm in diameter and 2 mm thick, were fabricated from each material (12 of shade A2 and 12 of shade A4) using flexible molds. Each specimen was prepared as one increment and light-polymerized from each side for 40 seconds using a QTH light unit with intensity of 850 mW/cm2 (Optilux 501, Kerr, USA). Specimens were polished with silicon carbide paper and each group of 12 specimens was subdivided into three subgroups (n=4), with each assigned to a bleaching agent. Specimens were stored in distilled water at 37°C for 24 hours and then subjected to bleaching using one of three in-office agents. Hydrogen peroxide concentration and pH of the bleaching gels as well as mode of application recommended by the manufacturers are listed in Table 1.