The effect of different bleaching strategies on the microhardness of silorane based composite resin

Abstract

In daily clinical practice there are existing tooth colored restorations in teeth which are planned for bleaching. Furthermore it is important to dentists to know the effect of bleaching agents on surface and mechanical characteristics of restorative materials. Aim:The purpose of this in vitro study was to evaluate the effect of 15% carbamide peroxide , 35% hydrogen peroxide and photo activated 35% hydrogen peroxide on the microhardness of the silorane based composite resin. Method and Materials: A total of 80 specimens (4 mm in diameter and 2 mm in thickness) of silorane based composite resins were fabricated in cylindrical acrylic molds. After polishing with sand papers(grits of 600,1000,2000,3000,5000) samples were randomly divided into 4 groups (n=20) according to bleaching strategy: group I(control) specimens were stored in distilled water for 2 weeks , group II specimens were treated with carbamide peroxide 15% for 2 hours per day for 2 weeks, group III specimens were bleached with hydrogen peroxide 35% for 30 minutes twice every 5 days and group IV specimens were treated under LED light with photo activated hydrogen peroxide 35% once for 40 minutes . The specimens were subjected to Vickers microhardness test.Data were analyzed using One-way ANOVA and Post hoc Tukey test(=0.05) Results : Analysis of variance and the Tukey tests showed that all of bleaching regimens decreased significantly the microhardness of silorane based composite resin (P<0.05). Furthermore there was significant difference between microhardness of group II and group IV(p=0.001).However there was no significant difference between microhardness of group II and group III. Conclusion: Bleaching agents decrease microhardness of silorane based resin composites. Decrease rate depends on bleaching strategy