Color changes of light-cured composite resins.

The color changes of light-cured composite resins over specified periods of time were examined. Silux Plus (3M Co.) light-cured composite resin disks (shades: U,Y,DY,L,G,UO,YO) 10 mm in diameter and 1 mm in thickness were made with 2 minutes of light exposure. Five specimens of each color were prepared. The specimens were stored in 37 degrees C artificial saliva. The colorimetric values of the specimens were measured first without a background color and then against a white plate immediately after curing and then 1 day, 1 month, 3 months, 6 months and 1 year later. The color measuring was performed with the Murakami Color Research Laboratory Fast Spectrophotometer CMS-500 and Flexible Sensor FS-3. For specimens without background color, the delta E*ab values of all shade guides increased for 6 months proportionately to the time elapsed. For specimens measured against a white plate, the delta E*ab values of all shade guides increased for 6 months after curing. However, compared to the 6 month delta E*ab values, the one year delta E*ab values increased in some shades and decreased in other shades. Using the values obtained immediately after curing as the standard, the delta E*ab of the month specimens with or with-out background color were over 1.2, meanwhile most one year specimens were near or over 2.5.