Effects of Food-Simulating Liquids and Thermocycling on Surface Roughness and Color Stability of Highly Filled Flowable Resin Composites

Highly filled flowable resin composites have been developed to improve the mechanical and esthetic performance of conventional flowable materials, but their long-term behavior under different aging conditions remains insufficiently characterized. This study evaluated the effects of thermocycling and food-simulating liquids on the surface roughness and color stability of five highly filled flowable resin composites with a nanohybrid flowable composite included as a reference material. A total of 240 cylindrical specimens were randomly assigned to thermocycling, 10% citric acid, n-heptane, or 75% ethanol groups (n = 10 per material and protocol). Surface roughness was measured before and after aging, and color change (ΔE*ab) was determined after subsequent immersion in coffee solution. Data were analyzed using two-way analysis of variance (ANOVA) to evaluate the main effects of material and aging protocol and their interaction, followed by Tukey’s post hoc test for multiple comparisons (α = 0.05). Aging-related changes in surface roughness and color stability varied according to both the material and aging protocol. Significant material × aging-protocol interactions were observed for both ΔRa and ΔE*ab (p < 0.001). GrandioSO Heavy Flow showed the greatest increase in surface roughness after ethanol and n-heptane aging and the highest mean ΔE*ab values under each aging condition, whereas Neo-Spectra ST Flow showed the highest mean ΔRa after thermocycling, and G-ænial Universal Injectable showed the highest mean ΔRa after citric acid exposure. These findings indicate that the aging response of highly filled flowable resin composites is material-dependent and provide insight into their relative behavior under different laboratory aging conditions.