Effects of Vitamin C-Containing Commercial Toothpastes on Surface Roughness and Microhardness of Composite Resins: An In Vitro Study

Background: The aim of this in vitro study is to comparatively evaluate the effects of toothpaste formulations containing and not containing vitamin C on the surface roughness and microhardness of different composite resin materials. Methods: Four different toothpastes (Sensodyne, Colgate, Klorhex, Dentiste) and three composite resin materials (Arabesk—microhybrid, Charisma Smart—nanohybrid, Estelite Sigma Quick—supra-nano filled) were used in the study. Composite discs measuring 10 mm in diameter and 2 mm in thickness were prepared and subjected to brushing simulations equivalent to 1 month (150 s) and 3 months (450 s). Surface roughness was measured using a mechanical profilometer, and microhardness was evaluated with a Vickers hardness tester. Surface morphology was further examined in detail using scanning electron microscopy (SEM) and atomic force microscopy (AFM). For statistical analyses, one-way ANOVA, repeated measures ANOVA, Kruskal–Wallis test, and Friedman test were employed, with the significance level set at p < 0.05. Results: Brushing procedures resulted in statistically significant changes in the surface roughness (ΔRa) and microhardness of the composites across all toothpaste groups (p < 0.05). The increase in surface roughness varied depending on the composite type, with the highest increase observed in the ESQ composite. In the ESQ composite, higher ΔRa values were obtained, particularly in the Dentiste (≈1.70 µm) and Colgate (≈1.52 µm) groups. Microhardness results, however, differed depending on the composite and toothpaste type. While a general trend toward increased microhardness was observed, a significant decrease in microhardness was detected in the Colgate and Dentiste groups of the ESQ composite (p < 0.05). Conclusions: This study demonstrates that the addition of vitamin C to toothpaste formulations increases the surface roughness of restorative materials and results in significant changes in their microhardness properties. These findings highlight the importance of considering the type of toothpaste used by patients in clinical practice, particularly in terms of restorative material selection and the long-term preservation of surface integrity.