Effect of Beverages with Varying Acidity on the Surface Microhardness of Resin Composites: An In Vitro Study

Introductions: The increasing consumption of acidic beverages has raised concerns regarding their impact on the longevity of composite resin restorations. Surface microhardness is a critical parameter for evaluating the mechanical performance and durability of restorative materials. Aim: To evaluate and compare the effect of beverages with varying acidity on the surface microhardness of different composite resin materials and to assess the relationship between beverage pH and microhardness reduction. Materials and Methods: This in vitro experimental study included 140 disc-shaped specimens of four composite resins: Filtek Z350 XT, Tetric N-Ceram, Beautifil II, and Charisma Smart (n = 35 per group; n = 7 per subgroup). Specimens were immersed in five media (Coca-Cola, Gatorade, orange juice, green tea, and distilled water) for 30 days. Surface microhardness was evaluated using the Vickers hardness test before and after immersion. Statistical analysis was performed using one-way ANOVA, Tukey’s post hoc test, and Pearson correlation (p < 0.05). Results: All composite resins exhibited a significant reduction in surface microhardness following immersion (p < 0.001). The greatest reduction was observed in Coca-Cola, while green tea and distilled water showed minimal effects. Beautifil II demonstrated the highest resistance to microhardness loss, whereas Tetric N-Ceram and Charisma Smart showed greater susceptibility. A strong negative correlation was observed between beverage pH and percentage microhardness reduction (r =–0.90, p = 0.002), indicating increased degradation with decreasing pH. Conclusions: Surface microhardness of composite resins is significantly influenced by beverage acidity and material composition. Giomer-based composites demonstrated superior resistance to acidic degradation. Consideration of patient dietary habits and appropriate material selection may help improve the longevity of composite restorations in acidic oral environments.