Color Stability of Single-Shade Resin Composites: A Systematic Review of In Vitro Studies and Clinical Implications

Background/Objectives: Modern restorative dentistry increasingly focuses on achieving optimal aesthetic integration while simplifying clinical procedures. Single-shade resin composites were introduced to reduce the complexity of conventional multi-shade layering techniques through enhanced color adjustment potential and structural color technology. However, concerns remain regarding their long-term color stability. The aim of this systematic review was to evaluate the color stability and aesthetic performance of single-shade resin composites compared with conventional multi-shade systems under different staining and aging conditions. Methods: This systematic review was conducted according to PRISMA 2020 guidelines and registered in the Open Science Framework. A systematic search was performed in PubMed, Scopus, and Cochrane Library up to 31 October 2025. Studies evaluating color stability using the CIEDE2000 (ΔE00) formula after staining and aging procedures were included. Risk of bias was assessed using the RoBDEMAT tool. Results: The search identified 169 records, of which 11 in vitro studies met the inclusion criteria. Across the included studies, discoloration increased progressively over time, and chromogenic agents frequently induced ΔE00 values exceeding clinical acceptability thresholds. Turmeric and red wine demonstrated the highest staining potential, whereas distilled water and artificial saliva showed minimal color variation. Single-shade composites generally exhibited greater susceptibility to discoloration than multi-shade systems, although variability among materials was observed depending on composition and experimental conditions. Conclusions: Single-shade resin composites simplify restorative procedures and provide initial aesthetic integration; however, they appear more susceptible to clinically relevant discoloration under experimental conditions. Further clinical and in vitro investigations are required to confirm these findings.