Surface roughness changes in bulk-fill resin composites after simulated toothbrushing with whitening toothpastes

Whitening toothpastes are widely used for the management of extrinsic tooth discolouration; however, their abrasive and chemical components may adversely affect the surface properties of resin based restorative materials. Surface roughness is a critical parameter influencing plaque accumulation, discolouration, and long-term aesthetic performance. Therefore, the aim of this in vitro study was to evaluate the effect of simulated toothbrushing with five different whitening toothpastes on the surface roughness of bulk-fill resin composites. Two bulk-fill resin composites (GrandioSO x-tra and Filtek Bulk Fill Posterior) and one nanohybrid composite (Clearfil Majesty Esthetic) were investigated (n = 60 per material). Specimens were randomly assigned to five whitening toothpaste groups (Opalescence Whitening, Colgate Optic White, Rocs Sensation Whitening, Signal White Now, and Curaprox Black Is White) and a distilled water control (n = 10). Simulated toothbrushing was performed using an electric toothbrush under a constant force of 2 N for 5 and 30 min, corresponding to approximately two months and one year of clinical brushing. Surface roughness (Ra, µm) was measured using a contact profilometer. Changes in roughness (ΔRa) were analyzed using two-way ANOVA and Bonferroni post-hoc tests (α = 0.05), with effect sizes calculated as partial eta squared (ηp²). Toothpaste formulation, composite type, and their interaction significantly influenced surface roughness at both brushing durations (p < 0.001). After 5 min, significant differences were mainly observed for Clearfil Majesty Esthetic. After 30 min, surface roughness increased markedly for all composites, with very large interaction effects (ηp² = 0.832). Toothpastes containing optical agents, enzymatic components, or activated charcoal produced greater ΔRa values, whereas Opalescence Whitening showed changes comparable to the control in some groups. Mechanical brushing alone also resulted in measurable roughness increases. Whitening toothpastes significantly affect the surface roughness of bulk-fill resin composites in a material and time dependent manner. Prolonged brushing amplifies surface degradation, and dentin-based abrasivity indices alone may not fully explain or predict composite surface alterations. Clinicians should consider the potential long-term effects of whitening dentifrices on existing resin based restorations.