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. Objective: 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. Materials and Methods: 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. Results: 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. Conclusions: 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.