Comparative Evaluation of the Color Stability of Monochromatic Versus Polychromatic Resins after Coffee Staining: An in vitro Study

Abstract

Aims: This in vitro study aimed to evaluate and compare the color stability and color match of a monochromatic versus a polychromatic composite resin after a coffee staining protocol. Study Design: This study employed an in vitro, randomized, and blinded comparative experimental design. Place and Duration of Study: Department of Dentistry, State University of Western Paraná (UNIOESTE), between June 2024 and July 2025. Methodology: Fifteen extracted human molars (totaling 30 cavities) with standardized Class V cavities were restored with either a monochromatic resin (Omnichroma) or a polychromatic resin (Filtek Z350 XT, shade A3). The specimens were subjected to two staining cycles designed to simulate 10 months of coffee consumption. Two blinded clinicians visually assessed the color match at baseline (T1), after the first cycle (T2), and after the second cycle (T3). Data were analyzed using Mann-Whitney and Friedman tests (α=0.05). Results: The polychromatic resin, Filtek Z350 XT, demonstrated a superior color match at baseline (P=.007), whereas the monochromatic resin, Omnichroma, performed significantly better after the first staining cycle (P=.004). At the final assessment (T3), both materials showed similar, though diminished, color compatibility (P=.784). Inter-rater reliability for the visual assessment was poor (Cohen's Kappa = 0.179), indicating significant subjectivity. Conclusion: The monochromatic resin provided long-term aesthetic performance comparable to the conventional polychromatic resin. These findings confirm its viability as a clinical alternative and highlight the limitations of subjective visual assessment, suggesting a need for instrumental analysis in future studies.