Under-surface hardness of light-cured nanofilled resin composites of different shades

The objective of the this study was to analyze the under-surface hardness of light-cured nanofilled composite resins of different shades. The specimens were resin composites of each light (B1), medium (A3), and dark (C3) shades packed in a cylinder mold and subsequently polymerized. The hardness was tested using a Knoop system. The hardness test results for the bright (B1), medium (A3), and dark (C3) shades were 82.4+1.1, 75.9+1.2 and 65.9+1.9, respectively, and indicated significant differences between the under-surface hardness of each shade. It was concluded that resin composites of darker to brigher shades demonstrated lower to higher under-surface hardness.