Output from visible-light activation units and depth of cure of light-activated composites

A simple and reproducible method for monitoring the intensity of radiation from composite light-activation units has been developed. The method depends upon the use of a cadmium sulfide photo-conductive cell, the electrical resistance of which varies with the amount of light falling upon its surface. Filters were used for selection of the wavelength of light that is thought to be most effective in activating polymerization. The use of broad-band wavelength filters failed to give results for light intensity that correlated with depth of cure. Narrow-band interference filters, having a band width of only 10 nm and being selective within the wavelength range of from 460 to 480 nm, produced results for light intensity that correlated with depth of cure. The depths of cure for various types of composite material were measured with use of a penetrometer that enabled the thickness of unpolymerized material at the base of the test mould to be determined. The depth of cure was inversely proportional to the attenuation of light caused by the composite resin at 470 nm. The relationship between depth of cure and light intensity at 470 nm was not a simple linear one over all intensity values. Above a certain critical value of intensity (about 550 lux for a 3.5-mm aperture in these experiments), the depth of cure appeared to be almost independent of intensity. Below this critical value, depth of cure fell markedly with decreasing intensity.