Comparison of Color Stability Between Single-Layer Bulk-Fill Composites and Bilayer Conventional and Bulk-Fill Composites

This study aimed to evaluate the color stability and translucency of bulk-fill resin-based composites when used alone versus when capped with a conventional composite resin. Three bulk-fill composites (Tetric N-Ceram Bulk Fill, Beautifil-Bulk Restorative, and Filtek One Bulk Fill Restorative) and one conventional composite (Filtek Z250 Universal Restorative) were used. A total of 48 disk-shaped specimens (diameter: 10 mm, thickness: 2 mm) were fabricated using three types of bulkfill composites and one conventional composite resin. In addition, 36 bilayered specimens were prepared by combining 1 mm of each bulk-fill composite with a 1 mm layer of a conventional composite resin on top. Color measurements were conducted using a spectrophotometer, and the specimens were stored in either distilled water or tea for four weeks. Color differences (ΔE*ab) were calculated based on the Commission Internationale d’Eclairage L*a*b* system, and translucency parameters were determined. While color stability was maintained in distilled water, immersion in tea caused significant discoloration, exceeding both the perceptibility and acceptability thresholds. Tetric N-Ceram Bulk Fill exhibited the highest color stability, followed by Filtek One Bulk Fill Restorative and Beautifil-Bulk Restorative. Bulk-fill composites with a capping layer demonstrated similar or superior color stability to that of uncapped specimens. The translucency of the bulkfill composites was higher than that of the conventional composites, with the bilayer specimens showing intermediate values. Therefore, capping bulk-fill composites with a conventional composite resin may improve long-term color stability while slightly reducing translucency, ultimately enhancing esthetic outcomes in posterior restorations.