The difference in degree of conversion between light-cured and additional heat-cured composites.

This study was designed to determine the changes in the degree of conversion throughout composite resins of varying thicknesses after heat curing and to evaluate whether or not the thin wafer technique that was applied in this study was sensitive to changes in distance from the light source. A 5 mm-in-diameter hole was made in a 4 mm-thick Teflon plate, and composite resin was placed in the hole and light cured from the top for 60 seconds. Twenty samples were prepared; 10 of these were additionally heat cured in an inlay oven. After light curing or light and heat curing, the samples were sectioned into four parts and assigned to groups A, B, C, or D according to their distance from the light source. These sections were then thinned to 50-70 microns, and analyzed by use of a standard baseline technique with a Fourier Transform Infrared Spectrometer (FT-IR) to determine the degree of conversion. The degree of conversion diminished as the distance from the light source increased; however, once the samples were heat cured, significant increases in the degree of conversion were noted throughout the samples. In the heat-cured composites, the degree of conversion in the outer portion of the sample was higher than in the inner portion. The thin wafer technique with FT-IR is considered to be a reliable method for measuring the degree of conversion in a composite resin, because changes between groups were clearly noted.