Influence of tooth whitening on the surface hardness of three composite resins: An In Vitro Study
Keywords: Microhardness; Composite resins; Tooth whitening.
This study aims to evaluate in vitro the surface hardness of three polymerizable composite resins (Filtek Z350 - 3M ESPE, Zirconfil - TECHNEW, Vitra - FGM), after a 40% hydrogen peroxide tooth bleaching process. 60 specimens were made, 20 specimens of each restorative material (n=20). After the finishing and polishing process, the specimens were randomly divided into two groups for each restorative material (n=10), where the control group G1 was maintained in artificial saliva and the test group G2 was subjected to bleaching gel based on of 40% hydrogen peroxide according to the manufacturer's instructions. For each specimen, four consecutive and equidistant readings were performed, with a load of 300g of force for 15s. Hardness values for tested resins were correspondingly higher in the control group than in the test group. The biggest difference in the mean values between the groups occurred in the Z350XT resin and for the fixed margin of error (5%) a significant difference (p < 0.05) between the test and control groups for each resin. The hypothesis tested in this test was null, since there were significant changes between the hardness of the control group and the test group, thus showing that the bleaching gel altered the hardness of the tested resins.