Optical properties and staining susceptibility of single-shade composite resins and their conventional counterparts

The objective of the present study was to compare the color, translucency, and staining susceptibility of single-shade and conventional composite resins. A total of 48 cylindrical specimens (6 mm in diameter × 2 mm thick) were fabricated using 2 conventional composite resins (Palfique and Vittra APS) and 2 single-shade composite resins (Omnichroma and Vittra APS Unique) from the same manufacturers (n = 12 per material). The specimens were subjected to color analysis with a digital spectrophotometer to determine the coordinates within the International Commission on Illumination (CIE) L*a*b* system, and a shade guide unit (SGU) score was recorded using the VITA classical shade guide. The translucency parameter (TP00) was calculated as the difference in color readings obtained on white and black backgrounds. Color readings were performed at baseline and after specimens were immersed in a coffee solution for 7 days. Overall color differences were calculated as ΔE*ab and ΔE*00 values. Data were analyzed using generalized linear models for the variables L*, b*, ΔE*ab, ΔE*00, and TP00, while Kruskal- Wallis, Dunn, and paired Wilcoxon tests were applied for the variables a* and SGU (α = 0.05). After staining, the L* value decreased while the a* and b* values increased in all composite groups (P < 0.001). The single-shade resin Vittra Unique presented higher L* and lower b* values than all other materials as well as lower a* and SGU values than the conventional resins (P < 0.001). The single-shade resin Omnichroma presented higher initial translucency than its conventional counterpart Palfique; after staining, both single-shade resins presented higher translucency than the conventional resins (P = 0.001). The overall color change of the 4 materials was not significantly different (ΔE*ab: P = 0.063; ΔE*00: P = 0.135). In this study, single-shade composite resins presented color stability similar to that of their conventional counterparts and demonstrated greater translucency and luminosity.