Combined Effects of Simulated Gastric Acid, Coffee Immersion, and Cleaning Procedures on the Surface Topography and Optical Properties of Flowable Resin Composites

The durability of dental restorations against erosive and staining challenges is crucial for long-term clinical success. Therefore, this in vitro study aimed to investigate the combined effects of sequential simulated gastric acid exposure, coffee immersion, and different cleaning procedures on the surface roughness and color stability of four contemporary flowable resin composites with different filler and matrix characteristics. Ninety-six disk-shaped specimens were fabricated from four resin composites: Omnichroma Flow, G-ænial Universal Injectable, Universal Flo, and EverX Flow. Baseline surface roughness and color coordinates were recorded. Specimens were immersed in 0.06 M hydrochloric acid for 48 h to simulate gastric acid exposure and subsequently immersed in coffee solution for 24 h to simulate staining. Color measurements were performed at baseline, after sequential gastric acid–coffee exposure, and after cleaning procedures. ΔE0 was calculated between baseline and post-exposure values, whereas ΔE1 was calculated between post-exposure and post-cleaning values. Specimens were then allocated to three cleaning subgroups: toothbrushing (BR), water flosser (WF) and mouthrinse (MR). Final surface roughness and color changes were evaluated. Data were analyzed using mixed and factorial ANOVA tests. Sequential gastric acid–coffee exposure significantly increased surface roughness in all materials. Omnichroma Flow showed the lowest roughness values, whereas G-ænial Universal Injectable demonstrated the highest post-treatment roughness, particularly after toothbrushing. Toothbrushing generally caused greater roughness increases than other cleaning procedures. Material type significantly affected color stability, with Universal Flo showing the greatest discoloration and Omnichroma Flow the lowest color change. Surface roughness and color stability were significantly influenced by sequential gastric acid–coffee exposure and cleaning procedures in a material-dependent manner.