A Standardized In Vitro Procedure For Evaluating Surface Microhardness Changes In Nanohybrid Resin Composites After Whey Protein Beverage Exposure.

The aim of this in vitro study was to evaluate the effect of different whey protein beverages on the surface microhardness of three nanohybrid resin composites. A total of 90 disc-shaped specimens were prepared from three nanohybrid resin composites (n = 30 per material) and subdivided into three groups (n = 10) according to the immersion medium: whey concentrate, whey isolate, and distilled water. The specimens were immersed for 10 min twice daily for 30 days. Surface microhardness was measured at baseline and after immersion using a Vickers microhardness tester, and hardness change was calculated as ΔVHN. The data were analyzed using two-way repeated measures ANOVA and post-hoc tests. The analysis revealed that composite type, immersion solution, and their interaction had statistically significant effects on ΔVHN values (p < 0.0001). The highest hardness loss was observed in the injectable composite exposed to whey concentrate (ΔVHN: 10.4 ± 2.1), whereas the lowest change was recorded in the highly filled composite stored in distilled water (ΔVHN: 0.9 ± 0.4). Immersion in whey concentrate resulted in significantly greater hardness loss in all composites compared to distilled water (p < 0.05). Whey isolate also produced significantly greater hardness loss in all composites except the highly filled composite, in which no statistically significant difference was observed (p = 0.076). These findings indicate that whey protein beverages may reduce the surface microhardness of resin composites, with the extent of degradation depending on both material composition and beverage formulation.