Hydrogen Peroxide Diffusion and Optical Response in a Universal Composite Resin: A Spectrophotometric In Vitro Investigation with Clinical Implications.

Background: The aim of this in vitro study was to evaluate the extent to which a hydrogen peroxide-based whitening agent penetrates a universal composite resin and induces optical changes detectable by spectrophotometry. Material and Methods: 60 rectangular-shaped composite specimens were fabricated and finished using a standardized protocol, then divided into two groups based on the polishing method used: 30 specimens were polished with a single-step polishing system (Enhance), and the remaining specimens were polished with a two-step polishing system(Astropol). Each group was further divided into two subgroups based on the ageing solution in which they were submerged after polishing: red wine (study groups) or physiological solution (control groups). Specimens then underwent ageing and were exposed to a 40% peroxide gel at predefined intervals. Color measurements (L*, a*, b*) were recorded before and after treatment and overall color difference (Eab*) was computed according to the CIE L*a*b* formula. Statistical analysis was performed using software and applying Wilcoxon's W test and Welch's t test. Results: In both study groups, a statistically significant difference in Eab* values was found between the measurement points after bleaching (p < 0.05). Between-group comparisons showed statistically significant differences in lateral Eab* after bleaching (p < 0.05). All measurement points achieved final Eab* values 3.3 following whitening treatment. Conclusions: Within the limitations of this study, hydrogen peroxide-based systems appear capable of diffusing into universal composite resins and altering their optical properties. Furthermore, the bleaching effect appears to be greater in specimens polished using a single-step method.