effect of different bleaching strategies on microhardness of a silorane-based composite resin

background and aim(s): it is highly important for dentists to be aware of the effects of bleaching agents on the surface and mechanical properties of restorative materials. so, the aim of this in vitro study was to evaluate the effects of different bleaching strategies on the microhardness of a silorane-based composite resin. materials and methods: eighty samples of a silorane-based composite resin (4 mm in diameter and 2 mm in thickness) were prepared inside acrylic molds. the samples were polished and randomly divided into 4 groups (n=20). group 1 (controls) were stored in distilled water for 2 weeks. the samples in group 2 underwent a bleaching procedure with 15% carbamide peroxide for two weeks 2 hours daily. the samples in group 3 were bleached with 35% hydrogen peroxide twice 5 days apart for 30 minutes each time. the samples in group 4 underwent a bleaching procedure with light-activated 35% hydrogen peroxide under led light once for 40 minutes. then the microhardness of the samples was determined using vickers method. data were analyzed with one-way anova and post hoc tukey tests (p 0.05). conclusion(s): bleaching agents decrease microhardness of silorane-based composite resin restorations, the extent of which depends on the bleaching strategy applied.