The Effect of Food-Simulating Liquids and Thermal Aging on Surface Roughness and Color Stability of Bulk-Fill and Conventional Composites

Objectives: The aim of this study was to evaluate the effect of food-simulating liquids (FSLs) and thermal aging on the surface roughness and color stability of bulk-fill and conventional composites. Materials and Methods: A total of 320 disc-shaped samples were prepared, with 40 samples from each of 4 different bulk-fill composites (Filtek Bulk Fill, X-tra fil, Beautifil Bulk Restorative, and Estelite Bulk Fill Flow), and 4 conventional nano-filled composite resins (Filtek Z550, CeramX SphereTEC one, Admira, and Kalore). The prepared samples were randomly divided into subgroups for exposure to FSLs (ethanol, heptane, citric acid) and thermal cycling (TC) (n=10 per subgroup) for 28 days. Initial profilometric surface roughness measurements (Ra0) of all samples and AFM and SEM analyses of selected samples were followed by exposure to FSLs and TC. After completion of aging protocols, measurements and analyses were repeated to obtain the Ra1 (post-treatment surface roughness), and change in surface roughness (∆Ra1-0) was then calculated. Subsequently, initial color measurement of the samples was conducted using a spectrophotometer, followed by immersion of the samples in a coffee solution for 24 hours. Color measurements were repeated, and color change (∆E) was calculated. Two-way repeated measures ANOVA was used to compare Ra0 and Ra1 values and one-way ANOVA for comparing ∆Ra and ∆E values. Tukey and post hoc tests were employed for pairwise comparisons. The significance level was set at α=.05. Results: While the surface roughness of bulk-fill composites was affected by the protocols applied (p<0.05), conventional composites generally remained unaffected. Bulk-fill composites exhibited greater ΔRa and ∆E values. The highest ∆Ra and ∆E values were observed in the Beautifil Bulk Restorative group, with the greatest discoloration seen after immersion in citric acid. Conclusions: Thermal cycling and immersion in FSLs affect surface roughness and color stability of composite resins depending on the content and structure of the composites.