A survey of the effectiveness of dental light-curing units and a comparison of light testing devices

The aims of this study were to: 1. survey the light output from 49 light-curing units in clinical use; 2. measure the effect on depth of cure of composite resin caused by a range of light outputs; 3. assess the relationship between radiometer meter readings and depth of cure of composite resin in a human tooth model and a Heliotest. The mean meter reading produced by the 49 lights surveyed using a lampChecker radiometer was 4.4 (+/-2.4 SD), range 0.3 to 10.0. The manufacturer of the radiometer considers optimal light output to provide a meter reading within the range 5.0 to 7.0. Lights of very low output (0.7 +/- 0.1 SD) were found to be capable of curing, after 20 seconds, a 1.9 (+/-0.3 SD) mm thickness of composite resin. However, only approximately 50% of this thickness can be considered fully cured. Increasing the cure time from 20 seconds to 60 seconds increased the mean depths of cure by a factor of approximately 1.4. The mean depths of cure of composite resin placed in the Heliotest were greater than those observed in the natural tooth model, by a factor of approximately 1.3. Correlation coefficients of meter readings and depth of cure were greater for the Efos Cure Rite and Demetron 100 radiometers than the lampChecker unit.