Effects of In-Office Bleaching and Repolishing on the Color Stability and Surface Roughness of Nano-Hybrid Resin Composites

Background: To evaluate the effects of in-office bleaching treatment on color and surface roughness of nano-hybrid resin composites (NH-RC) and the impact of different repolishing procedures following bleaching. Methods: Sixty disc-shaped (8 × 2 mm, A2) specimens were prepared using 2 different NH-RC (Charisma Topaz One, Kulzer, Germany; Parion, Dentac, Türkiye). Initial finishing and polishing processes were completed with 4-stage discs (OptiDisc, Kerr). Excluding the control groups (n = 10), 40 specimens were subjected to 2 sessions of office bleaching (40% hydrogen peroxide, Opalescence Boost, Ultradent), each consisting of three 20-minute applications at 3-day intervals. After 24 hours, half of the bleached specimens from each composite group were repolished with a 4-step disc system (OptiDisc, Kerr), and the others with diamond-impregnated silicone rubbers (DiaComp Plus Twist, Eve). Surface roughness (Ra) was recorded with a profilometer (SJ-210, Mitutoyo, Japan) and color was analyzed with a spectrophotometer (Easyshade V, VITA, Germany) at baseline, after bleaching, and after repolishing, respectively. Color changes (ΔE) were calculated with the CIEDE2000 formula. The data were evaluated statistically by 2-way ANOVA and Bonferroni test (P < .05). Results: In Parion, bleaching significantly increased surface roughness (P < .05) and ΔE₁-ΔE₂ values (>1.8; P < .001), exceeding the acceptability threshold, whereas the control remained below the 0.8 perceptibility limit. Repolishing reduced roughness (P < .05) and ΔE₃ values (0.8- 1.8) regardless of the repolishing system used, indicating acceptable matches. In Charisma Topaz One , no group showed ΔE₀₀ ≥ 1.8 or significant roughness changes (P > .05). Conclusion: Bleaching affects resin composites differently depending on their composition, but repolishing enhances color and surface properties regardless of the system used.