The objective of this study was to evaluate whether any coating material would have a beneficial influence on maintaining color stability and surface roughness, and to what extent an uncoated resin composite can keep its original color. The study evaluated three direct composite resins (Gradia Direct Anterior A2, Tetric EvoCeram A2, Filtek Z550 A2) using 30 samples per material (1 mm thick, 14 × 10 × 1 mm). Samples were prepared in 3D-printed molds, light-cured for 40 seconds, and initially smoothed with abrasive paper (grit 400–2000). The surface treatments applied were as follows: group 1—polished with a brush and Compo + polishing paste; group 2—conditioned with 37% phosphoric acid, with single bond adhesive applied, light-cured.

All samples were cleaned ultrasonically for 5 minutes. Initial surface roughness and color were measured with a profilometer and spectrophotometer. Samples were then immersed in distilled water (control), Coca-Cola (at 37 °C ) and red wine (at 10 °C), with surface roughness and color changes measurements taken on days 1, 7, and 14. Immersion media were refreshed weekly.

The most notable color changes after immersion in coloring solutions were observed in the groups treated with Coca-Cola and red wine, compared with the control group in distilled water. Statistically significant differences were found between the four evaluation stages, with the most pronounced changes occurring after 2 weeks of immersion.
This study simulates the oral environment and the exposure of restorative materials to staining agents. As the loss of esthetic properties over time is a continuous problem, the clinical significance of this research lies in demonstrating how a restorative material could resist pigmentation, when in contact with well- known high staining beverages, in order to maintain its esthetic properties and remain suitable for long-term use in the oral cavity. Moreover, the hypothesis that a coating material would protect the resin composite surface and reduce discoloration was tested.