The combined effect of light-illuminating direction and enamel rod orientation on color adjustment at the enamel borders of composite restorations.

To investigate the effect of light-illuminating direction (from composite or enamel side) on color adjustment at the coronal and cervical enamel borders in composite restorations. Forty cylindrical holes (3.0-mm diameters) were prepared in bovine enamel disks (1.0-mm thickness). After application of a one-step self-etch adhesive, one of four resin composites (Estelite Asteria, EA; Estelite Pro, EP; Kalore, KA; Clearfil Majesty ES-2 Premium, MJ) was restored in the holes. After 24-h storage, the colors (L*, C*, or h* values) at the restored enamel disks over a black background were measured in a black box using a CIE XYZ camera, spotted with D65 standard illuminant either from coronal or cervical side at 45°/0° geometry. The color shifting rate was calculated at the coronal and cervical enamel borders of the composite restorations, and analyzed by three-way ANOVA with Dunnett's T3 and t test for post hoc analysis (p < 0.05). The light-illuminating directions significantly affected the L* shifting rate at the cervical enamel border in EP and MJ (p < 0.05), and the C* shifting rate at the coronal enamel border in EA, EP, and MJ (p < 0.05). The color appearance at the border of the composite restoration was influenced by the light-illuminating direction in conjunction with the enamel rod orientation in the coronal or cervical enamel border. The line-of-vision angle would affect the perception of color adaptation at the enamel borders in the composite restorations.