Changes of optical properties of dental nano-filled resin composites after curing and thermocycling.

The objective was to evaluate the color changes after curing, polishing, and thermocycling of a nano-filled resin composite. A nano-filled composite was grouped into two shades of enamel (EN) and translucent (TL). One hybrid composite was used as a control (CL). Color of specimens of 10 mm in diameter and 2 mm in thickness was measured on a reflection spectrophotometer with SCE geometry under the D65 illumination over white and black backgrounds. Color before curing and after curing, polishing and thermocycling was measured. Color change (DeltaE(*) (ab)), translucency parameter (TP), and contrast ratio (CR) were compared. Average DeltaE(*) (ab) after curing was 4.6 in the EN group and 10.4 in the TL group compare to 2.9 in CL. Polishing caused average DeltaE(*) (ab) of 3.3-3.6, which was not different by the shade group (p > 0.05). After 2000 cycles of thermocycling, average DeltaE(*) (ab) was 1.4-1.8, which was not different by the shade group (p > 0.05). TP values increased after curing in the EN group, but decreased in the TL group (p < 0.05). TP values after thermocycling decreased in the EN group but did not change in TL (p = 0.05). TP values of TL shades were higher than those of EN regardless of specimen conditions (p < 0.05). Changes in CR values showed similar trends to those of TP values in translucency. Changes of color and translucency after curing, polishing, and thermocycling varied by the shade group.