Five-year color changes of light-cured resin composites: influence of light-curing times

Objectives: The purpose of this study was to investigate the influence of light-curing times on the color changes of light-cured resin composites, over specified periods of time. Methods: Silux Plus (3M Dental Products) light-cured resin composite disks (shades: U, Y, DY, L, G, UO, YO), 10 mm in diameter and 1 mm in thickness were prepared with 20, 40, and 120 s of light exposure through a 1 mm thick glass plate. The specimens were stored in artificial saliva at 37°C. Colorimetric values of the specimens immediately after curing and after every 6 months for 5 years were measured backed by a light trap, and a white colored plate using a fast spectrophotometer. The CIE 1976 L*a*b* color system was used for the determination of the color difference. Results: For specimens backed by a white colored plate, the ΔE*ab of all shades increased for 3 years and 6 months to 5 years, to the time elapsed during all curing times. However, the a*b* values to the time elapsed differed among the shades and light curing times. In the 20 and 120 s curing time groups, the opacity% of all shades increased for 4 or 5 years to the time elapsed. Significance: The modes of color changes of Silux Plus resins differed among the shades and light curing times.