[Curing ability of polymerization lights for composite materials]

An in-vivo study has been conducted with four different brands of activator light sources. 38 light units in service by different dental practitioners were compared with new light sources. Curing depth profiles were obtained using Knoop microhardness measurements. It was observed that with an exposure time of up to 60 s the polymerization was not sufficient below 2 mm of depth. The "old" light sources showed worse curing properties than the new ones, especially below this depth. Generally, the polymerization units with rigid glass fiber light guide showed better results than the units with a flexible fiber-optic cable. Other reasons for insufficient polymerization were polymerized composite material at the end of the light guide, a defect in the cooling system of the light source and, for two brands of light sources, a reduction of the voltage below 220 V.