Surface microhardness of three Bulk Fill resin composites previously exposed to five carbonated beverages at different times: an in vitro study

Background: Surface microhardness (SM) is a desirable property of any restorative material because it allows it to resist masticatory forces and any chemical challenges encountered in the oral environment. Therefore, the aim of this study was to evaluate the in vitro surface microhardness of three Bulk Fill resins previously exposed to five types of carbonated beverages at different times. Methods: This in vitro experimental study consisted of resin composite discs (n = 180), distributed in three groups: Tetric N-Ceram Bulk-fill, Opus Bulk Fill APS and Filtek Bulk Fill, each immersed in distilled water (control), Fanta^®, Sprite^®, Coca-Cola^®, Inca-Kola^® and Pepsi^®. Surface microhardness was measured before and after immersion in beverages for 1 day and 7 days. Data were subjected to statistical analysis using Games Howell’s robust ANOVA with post hoc and Friedman’s test with Bonferroni’s post hoc. Statistical significance was set at p < 0.05. Results: After 1 day of immersion, the Tetric N-Ceram Bulk Fill resin significantly decreased its surface microhardness after immersion in Fanta, Sprite, Coca-Cola, Inca-Kola and Pepsi (p < 0.05), while the Filtek Bulk Fill resin significantly decreased its SM after immersion in Pepsi and Sprite (p < 0.05); however, the Opus Bulk Fill resin showed no significant SM differences (p = 0.141). On the other hand, after 7 days of immersion, the three Bulk Fill resins significantly decreased their SM, compared to the control group (p < 0.001), after being immersed in the five carbonated beverages. Finally, distilled water did not significantly affect the surface microhardness of the three Bulk Fill resins over time (p < 0.05). Conclusion: This study highlights the susceptibility of Bulk Fill resin composites to acidic degradation caused by carbonated beverages. While short-term exposure resulted in variable effects depending on the resin type, prolonged immersion consistently led to a reduction in surface microhardness across all materials tested. These findings suggest that the chemical composition of each resin influences its resistance to erosive challenges. Although this is an in vitro study, the results may provide a basis for future investigations into how acidic diets could influence the long-term performance of Bulk Fill composites in the oral environment.