An AFM evaluation of the effect of 37.5% hydrogen peroxide on sealed and unsealed aged composite materials

Objective: The aim of this study was to evaluate the surface roughness of sealed and unsealed composite resins bleached with 37.5% hydrogen peroxide. Materials and Methods: Eight discs, 9 mm in diameter and one mm in thickness, were prepared from two shades (A1) of two composite resins, i.e. Filtek Z250 and Filtek Z350 XT. The specimens were polished and subjected to accelerated aging before bleaching. Half of the surface of each specimen was sealed with BisCover LV. Surface roughness was determined using Atomic Force Microscope (AFM) software before and after bleaching; 37.5% hydrogen peroxide was applied to the specimens for bleaching, and surface roughness was measured with AFM software. Surface roughness was evaluated by three parameters, i.e. roughness profile (Ra), height of the profile (Rz), and width of the profile (Rq). Data were statistically analyzed by two-way repeated measures ANOVA and t-test. Results: The arithmetical mean deviation of the Ra parameter of the specimens did not change significantly after bleaching with 37.5% hydrogen peroxide (P=.450). The mean Rq of the sealed specimens changed significantly after bleaching with 37.5% hydrogen peroxide (P=.002), and the maximum Rz parameter of the sealed and unsealed Filtek Z250 specimens, treated with 37.5% hydrogen peroxide, was significant (P<.005). Conclusions: Bleaching with 37.5% hydrogen peroxide had no significant effect on the nanofilled composite resin (Filtek Z350) and significantly decreased the surface roughness of unsealed Filtek Z250 in Rz parameters. In addition, bleaching of the sealed composite resin with 37.5% hydrogen peroxide resulted in an increase in the Rq parameter and a decrease in the Rz parameter. After bleaching, the sealed composite resin had the least surface roughness.