Effect of light intensity and exposure duration on cure of resin composite

Of the many factors under their control, clinicians can manipulate light-exposure duration but must deal with a set intensity of light emitted from the dental curing unit. This research investigates the interdependence of exposure duration and source intensity on resin cure at various depths within a simulated light-cured resin composite restoration. This wafers of composite were obtained from a simulated cylindrical restoration such that the wafer could be removed from the top or from a distance of 1, 2, and 3 mm beneath the surface. The composites used in this study were a microfill and hybrid of Universal and Gray shades. All the data concerning filler type and shade were pooled so that generalized statements could be made regarding curing of light-activated composite in general. Specimens were cured using various source intensities and for different durations at each level within the cured cylinder. The cure of the specimens resulting from the different treatments was determined using infrared spectroscopy. The results indicate a dramatic effect of depth on the cure of composite. At depths greater than 2 mm, poor cure results, and polymerization is very susceptible to changes in light intensity and exposure duration. From these results, routine exposure times of 60 seconds are recommended using light-source intensities of at least 400 mW/cm2 as measured with a commercial dental light intensity meter. Incremental layer thickness should not exceed 2 mm, with 1 mm being ideal. Sources with intensity values less than 233 mW/cm2 should not be used because of their poor cure characteristics.