Background <p>To evaluate surface microhardness, roughness, and gloss changes of tooth-colored restorative materials [a direct composite (G-aenial A’Chord), an indirect composite (Gradia Plus), an ormocer (Admira Fusion), a giomer (Beautifil II), and an alkasite (Cention N)] after exposure to simulated gastric acid.</p> Methods <p>A total of 110 disc-shaped specimens (22 discs of each material) were prepared using silicone molds (8&#xa0;mm×2&#xa0;mm) and exposed to either gastric acid or artificial saliva (control). Surface roughness (Ra), gloss (GU), and microhardness (VHN) were measured at baseline and after 96-hour of immersion in the solutions and the respective changes (∆Ra, ∆GU, ∆VHN) were calculated. Intergroup comparisons were performed using ANOVA (Tukey post hoc) or Kruskal-Wallis tests (Bonferroni correction). Independent samples t-test or Mann-Whitney U test was used for comparisons of each material across immersion media, while paired t-test was applied for time-dependent analyses.</p> Results <p>In the gastric acid medium, changes in all parameters led to significant differences among restorative materials, while in the artificial saliva medium, significant differences were observed in ∆VHN and ∆GU. The statistically significant difference between immersion media was observed in both ∆VHN and ∆Ra values for the giomer group, and in only ∆VHN values for the alkasite and indirect composite groups. In the gastric acid medium, the decrease in VHN and GU values was significant across all subgroups, while the increase in Ra was statistically significant only in the giomer and alkasite groups.</p> Conclusions <p>While the giomer group exhibited the most significant changes in roughness and microhardness following exposure to gastric acid, all tested materials executed clinically admissible results regarding surface gloss.</p> Clinical trial number <p>Not applicable.</p>