Effect of bleaching protocols on surface roughness and biofilm formation on silorane‑based composite resin

Knowledge about the effect of bleaching on behavior of composite resins is important to find a suitable composite resin for restoration of teeth undergoing bleaching. This study aimed to assess the effect of different bleaching protocols on surface roughness and biofilm formation on a silorane‑based composite resin. In this in vitro experimental study, 60 silorane‑based composite resin samples measuring 3 mm in thickness and 6 mm in diameter were fabricated and polished. They were then randomly divided into four groups (n = 15). In Group 1, samples were stored in distilled water as control. Samples in Groups 2, 3, and 4 were subjected to bleaching with 15% carbamide peroxide, 35% hydrogen peroxide, and 35% hydrogen peroxide activated by light, respectively. Surface roughness was measured using a profilometer. Streptococcus mutans cultured in brain‑heart infusion broth was used for the assessment of biofilm formation on the samples. The bacterial colonies were counted using the pure‑plate technique. Data were analyzed using one‑way ANOVA and post hoc Tukey’s tests. Regression model was used to assess the association between surface roughness and biofilm formation (P < 0.05). The mean surface roughness of the four groups was not significantly different (P = 0.11); however, a significant difference was noted in the mean biofilm formation among the groups (P = 0.00). Bleaching decreased biofilm formation. The lowest biofilm formation was noted in the group subjected to light‑activated 35% hydrogen peroxide. Increased surface roughness enhanced biofilm formation to a certain level; excessive roughness did not increase biofilm formation.