The purpose of this study was to investigate the color changes of light-cured composite resins over specified periods of time.
3M Co. light-cured composite resin Silux Plus(Shades: U, Y, DY, L, G, UO, YO) disks 10 mm in diameter and 1 mm thickness were prepared with 2 minutes 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 every 6 months for 3 years were measured without background color, backed by a white plate which was used to substitute for the lining material with a fast spectrophotometer.
The following results were obtained.
1) For specimens without background color, theΔE*ab values of all of thc shades except the G and YO shades increased proportionately to the time elapsed. For specimens measured against a white plate, the ΔE*ab values of all of the shades increased proportionately to the time elapsed.
2) For specimens without background color, the one-yearΔE*ab values ranged between 1.59(YO)and 2.67(L), the two-yearΔE*ab values ranged between 3.28(DY)and 4.94(L)and the three-year 4E*ab values ranged between 3.82(YO)and 6.06(L).
3) For specimens measured against a white plate, the one-yearΔE*ab values ranged between 2.28(YO)and 3.23(L), the two-yearΔE*ab values ranged between 4.19(YO)and 5.70(L)and the three-yearΔE*ab values ranged between 4.91(YO)and 7.04(L).
4) For specimens measured against a white plate, the L* values for all of the shades showed a tendency to decrease proportionately to the time elapsed. However, for specimens without background color, the L* values for many shades did not show the continuous decrease proportionately to the time elapsed.
5) Both in the cases of with and without background color, the a* values of all of the shades increased proportionately to the time elapsed and the green color factor decreased, however, theb* values showed different color changes proportionately to the time elapsed among the shades.
6) For three-year specimens with and without background color, significant correlations were obtained between ΔE*ab yalues and ΔL*, Δa* and Δb*values(P<0.01).