Color stability of ten resin-based restorative materials

Despite significant developments to improve the optical properties of composites, color stability remains a challenge with changes still observed immediately after polymerization and after some time of storage.

This study aimed to evaluate the color change of ten commercially available resin composite systems immediately after polymerization, at 24 hours, and at 1 month of water storage.

Five discs of two thicknesses (1 mm/3 mm) in two shades (A3/Bleach) were made from ten commercially available brands of resin composite. Color measurements were recorded with a colorimeter and expressed in terms of the CIE L*a*b* scale. Color change was calculated between baseline and immediate polymerization (ΔE*(1) ), between immediate polymerization and 24 hours (ΔE*(2) ), and between 24 hours and 1 month (ΔE*(3) ). Values ΔE* ≥ 3.3 were considered clinically unacceptable as color shifts over this threshold value may be noticeable. The results were analyzed using a three-way analysis of variance (ANOVA) and Student-Newman-Keuls's tests. A significance level of 0.05 was used for all tests.

Color change was evidenced for all brands, shades, and thickness. The greatest color change was observed immediately after initial polymerization with ΔE* values ranging from 2.4 to 12.0. Color change after 24 hours and 1 month were significantly less than those observed after polymerization. Immediately after polymerization, only Tetric EvoCeram (Ivoclar-Vivadent, Amherst, NY, USA) showed changes below 3.3. At 24 hours, 20 out of the 40 groups including all materials in both shades and thicknesses showed changes above 3.3. At 1 month, color changes for all brands remained under 3.3.

Overall, clinically relevant color changes (ΔE* ≥ 3.3) took place immediately after polymerization of current light-activated composites. These changes were predominantly attributed to shifts in the L* and b* parameters towards the dark and blue region, respectively. Color shifts continued at 24 hours with changes in the L* and b* parameters towards the light and yellow region, respectively. After 1 month, only minor changes under the 3.3 threshold took place.

Ensuring an accurate color match of resin composite restorations to the surrounding tooth structure is a critical aspect of any esthetic restorative procedure. A better understanding of the changes taking place during the different stages of maturation and storage of composites may be of significant benefit to clinicians as this may help minimize shade mismatch issues.