Abstract
The purpose of this study was to investigate the influence of the light-irradiating times on the color changes of light-cured composite resins over specified periods of time.
Composite resin disks which were 10 mm in diameter and 1 mm in thickness, and made of the 3M Co. light-cured composite resin Silux Plus (shades: U, Y, DY, L, G, UO, YO) were made with 20,40 and 120 seconds of light exposure through a 1 mm thick glass plate. The specimens were stored in 37°C artical saliva. Colorimetric values of the specimens immediately after curing,1 day,1 month,3 months,6 months and 1 year after curing were measured without background color, backed by a white plate which was used to substitute for the lining material. The color measurements were performed with the Murakami Color Research Laboratory Fast Spectrophotometer CMS-500 and the Flexible Sensor FS-3.
1) Both in the cases of with and without background color, the ΔE*ab of many shades increased for 6 months or 1 year proportionately to the time elapsed in the 120 seconds group and compared to the ΔE*ab of immediately after curing, the 1 month ΔE*ab of many shades highly increased in the 20 and 40 second groups.
2) In the cases without background color, compared to the ΔE*ab immediately after curing, the 1 year ΔE*ab of all shades except the L-color shade showed higher values in the 40 second group than those in the 20 and 120 second groups. In the cases backed with the white plate, compared to the ΔE*ab of immediately after curing, the 1 year ΔE*ab of all shades except the L and G-color shades showed higher values in the 20 and 40 second groups than those in the 120second group.
3) The shades in which the 1 year ΔE*ab was near or over 2.5 and detectable to the naked eye were as follows: In the cases without back ground color, L and UO in the 120 second group, all shades in the 40 second group and U, Y, L, UO and YO in the 20 second group. In the cases backed with the white plate, all shades in the 20,40 and 120 second groups.
4) The color changes of light-cured composite resins over specified periods of time were influenced with the light-irradiation times. The influence of the lightirradiation time was stronger in the 20 and 40 second groups than that in the 120 second group. The influence of the light-irradiation time was obvious in the cases backed by the white plate.
