Analysis of Surface Microhardness of Different Resin Composites After Prolonged Exposure to Simulated Gastroesophageal Reflux Conditions: An In Vitro Study

Objectives: This in vitro study evaluated the effect of prolonged exposure to aqueous solutions with different pH values on the surface microhardness of four commercially available resin composites, simulating conditions associated with gastroesophageal reflux disease (GERD). Methods: Fifty standardised discs were prepared for each composite resin and allocated to five groups: a non-immersed control group and four groups immersed in solutions at pH 2.5, 5.0, 7.4 or 8.0. Samples were stored at 37 °C, after surface microhardness was measured using Vickers test after 24 h and after 7 days of immersion. Statistical analysis was performed using repeated-measures ANOVA, followed by Tukey’s post hoc test and linear regression analysis (p < 0.05). Results: All the materials showed a significant reduction in surface microhardness after immersion compared with the non-immersed controls (p < 0.05). Flowable composites exhibited consistently lower microhardness values than packable composites, and microhardness generally decreased after 7 days compared with 24 h. Linear regression analysis identified the composite formulation (commercial product tested), composite type (packable or flowable), and immersion time as significant determinants of microhardness (p < 0.05). Overall, these findings indicate that prolonged aqueous exposure, rather than pH itself, was primarily responsible for the reduction in surface microhardness. Significance: Within the limitations of this in vitro study, composite formulation and immersion time had a greater influence on surface microhardness than solution pH. These findings may help guide the selection of restorative materials for patients with gastroesophageal reflux disease.