The effect of different whitening mouthwashes and simulated tooth brushing on surface roughness and microhardness of nanohybrid resin composite: an in vitro study

Abstract

Background: This study investigated the effects of whitening mouthwashes containing active ingredients on a nanohybrid resin composite’s surface roughness (Ra) and Vickers microhardness (VHN) under distinct brushing conditions. Methods: Fifty-four disc-shaped specimens (10 mm diameter × 2 mm thickness) were fabricated and randomly assigned to three experimental conditions (n = 18): distilled water (Control), Patent Blue V-containing mouthwash (Colgate Optic White, COW), and activated charcoal-containing mouthwash (Colgate Plax White + Charcoal, CPWC). Each group was subdivided into brushed and non-brushed subgroups (n = 9). Non-brushed specimens were immersed in 20 mL of the assigned solution at 37 °C for 6 h (T1) and 12 h (T2). Brushed specimens underwent 5 000 and 10 000 brushing cycles before immersion at T1 and T2, respectively. Surface roughness was measured using a contact profilometer, and microhardness was assessed with a Vickers hardness tester. Data were analyzed using three-way mixed ANOVA, one-way ANOVA, repeated measures ANOVA, and Bonferroni correction (α = 0.05). Results: Significant differences were observed in Ra values based on mouthwash type and brushing (p < 0.05), while VHN remained unaffected (p > 0.05). In non-brushed specimens, CPWC exhibited the highest Ra increase (31.2%, + 0.296 μm), significantly higher than Control (1.6%, + 0.015 μm, p = 0.001) and COW (5.9%, + 0.055 μm, p = 0.001). Under brushed conditions, CPWC again showed the most significant increase (33.3%,+ 0.311 μm,p = 0.012). Microhardness showed no statistically significant changes across time points or groups (p > 0.05). However, at T2, CPWC (non-brushed) presented the most significant reduction (− 3.38%, − 1.4 VHN), which was significantly lower than Control (+ 1.98%, + 0.8 VHN) and COW (+ 3.3%, + 1.3 VHN) (p = 0.001). A 5.33% increase (+ 2.1 VHN, p = 0.756) was observed in the brushed CPWC group. Conclusions: Activated charcoal-containing whitening mouthwashes significantly increased surface roughness, particularly under brushing conditions, indicating a synergistic effect of chemical and mechanical wear. Microhardness values remained stable, suggesting the preservation of the internal structure. These findings highlight the need for cautious recommendation of charcoal-based mouthwashes for patients with resin restorations due to potential surface degradation risks.