THE ATTENUATION OF RADIATION BY PORCELAIN AND ITS EFFECT ON POLYMERIZATION OF RESIN CEMENTS

The influence of porcelain thickness and opacity on the polymerization of two dual activated (microfine and hybrid) and one light irradiated (hybrid) resin cements was assessed by hardness measurements. The sur face microhardness values of the upper and lower surface of 1 mm thick resin cement specimens were determined. Specimens were polymerized us ing 40 s irradiation beneath different thicknesses and opacities of po rcelain discs. The results showed that increasing the thicknesses and opacity of the porcelain produced a statistically significant decrease in microhardness of the resin-based cements. The effect of attenuatio n is less for the microfine cement than for the hybrids. In the case o f hybrid cements, the light activated material performed better than t he dual activated cement.