Comparison of Color Stability Between PMMA and Graphene-Reinforced PMMA After Being Subjected to pH Changes and Coffee

Background/Objectives: Provisional restorations are widely used in fixed prosthodontics, and polymethyl methacrylate (PMMA) remains one of the most commonly used materials. Discoloration during intraoral service may compromise their esthetic acceptability. Graphene-reinforced PMMA has been introduced to improve material performance, although its color stability under simulated oral conditions remains insufficiently characterized. This study aimed to compare the color changes in conventional PMMA and graphene-reinforced PMMA after exposure to salivary pH variations and coffee, combined with simulated masticatory movements. Methods: Forty PMMA and forty graphene-reinforced PMMA (G-CAM) disk-shaped specimens (8 mm × 2 mm) were allocated to eight original experimental groups according to material and condition (pH 7, coffee, pH change, or pH change plus coffee), under simulated chewing movements. Color was recorded before and after the procedures using an imaging system, and values were converted into CIELAB coordinates. Statistical analysis included Wilcoxon, Mann–Whitney U, Kruskal–Wallis, and Bonferroni-adjusted pairwise comparisons, with a significance level set at p < 0.05. Results: Both materials exhibited measurable color changes after the experimental procedures. PMMA showed higher median ΔE values than graphene-reinforced PMMA in the coffee and pH change plus coffee conditions, where the differences between materials were statistically significant. The highest color changes were observed in PMMA exposed to coffee and to the combined pH change plus coffee protocol, exceeding the clinical acceptability threshold. Conclusions: Graphene-reinforced PMMA (G-CAM) showed greater color stability than conventional PMMA, although neither material can be considered completely color stable. The greatest color variation was observed in the groups exposed to pH change followed by coffee immersion, as reflected by ΔE values.