In vitro study on the microhardness modification of four composite materials determined by the application of two bleaching protocols

Aim of the study The purpose of this study was to evaluate the microhardness evolution of several finished and polished dental composites modified by bleaching materials, when applied to restoration surfaces. Material and methods Three microhybrid composites and one nano-filled composite that are used in dental restorations were selected. Using these composites, a series of samples were finished and polished over which the "Office Bleach" dental bleaching protocol with 40% hydrogen peroxide gel or the "Home Bleach" dental bleaching protocol with 16% carbamide peroxide gel was applied.Results For all composite types, the differences between the microhardness values corresponding to the control and bleaching groups were statistically significant (p < 0.05). Following the bleaching protocol with 40% hydrogen peroxide gel it was found that the microhardness of the samples decreased considerably compared to the control samples, and the lowest value was recorded for the GC G-aenial Anterior sample (after "Office Bleach"). Following the 16% carbamide peroxide bleaching protocol ("Home Bleach") it was noted that the microhardness of the samples was not as affected as for the samples bleached with 40% hydrogen peroxide.Conclusions For both the "Home Bleach" and the "Office Bleach" dental bleaching protocols, the differences between the variation in microhardness of the 4 types of composites (before and after bleaching) were statistically significant (p < 0.05), with the "Office Bleach" protocol proving to be the most aggressive for all types of composites.