Effect of a Combined Bleaching Regimen on the Microhardness of a Sealed Methacrylate-based and a Silorane-based Composite

Statement of problem: the use of tooth bleaching agents has been very popular treatmentin dentistry. the bleaching agents have an inherent potential to impair surface propertiesof existing composite resin restorations.purpose: this study evaluated the effect of a combined bleaching regimen on the surfacemicrohardness of a silorane-based and a sealed methacrylate-based composite.materials and method: forty-five specimens of methacrylate-based composite (ice) and 18 specimens of silorane composite (filtek silorane, 3m espe; usa) were prepared and randomly divided into 5 (1-5) and 2 (6-7) groups (n=9), respectively. after 8-week aging, groups 1 and 6 were remained with no treatment. in groups 2, 4 and 5, the specimens were covered by a surface sealant and light cured. in groups 3, 4, 5 and 7, the specimens were bleached with hydrogen peroxide 40% and then carbamide peroxide 20% for seven days. in group 5, after bleaching, the sealant was removed by polishing. surface microhardness was measured and the data were analyzed using one-way anova and tukey tests (α=0.05).results: the microhardness values of groups 2 to 4 were significantly lower than that of group1 (p <0.05). there was no significant difference among groups 1, 5, 6 and 7 (p> 0.05).conclusion: the combined bleaching regimen used in this study had a substantial negativeeffect on methacrylate and sealed methacrylate composites but not on silorane composite.polishing following the bleaching on the sealed composite yielded a hardness value similar to that of unsealed methacrylate composite (control).