Influence of ceramic thickness and curing mode on the polymerization shrinkage kinetics of dual-cured resin cements

Objectives. The purpose of this study was to assess how ceramic disc thickness and curing mode (light or chemical) affects the polymerization shrinkage of dual-cured resin cements and to evaluate the effect of the ceramic discs on the curing speed of the cements during light exposure. Methods. Six commercial resin cements, RelyX ARC, Bistite II, Duolink, Panavia F, Variolink II and Choice were used. Filler weight contents were determined by the ash method. Four ceramic discs with thicknesses of 0.5, 1, 2 and 4 mm, respectively, were made. The attenuation of light intensity due to the ceramic discs was measured using a radiometer. The polymerization shrinkage kinetics of the resin cements by chemical or light cure through the different ceramic discs was measured using a bonded-disc method. Results. There were differences in filler content among brands of resin cement. The polymerization shrinkage without ceramic disc was 2.61-4.59% by chemical cure and 2.93-4.66% by light cure. The polymerization shrinkage of RelyX ARC and Panavia F by chemical cure was statistically lower than by light cure (p < 0.05). Polymerization shrinkage and filler weight were inversely related (R = -0.965). Both the transmitted light intensity and polymerization shrinkage decreased with increasing thickness of ceramic discs (p < 0.05). The time to reach the maximum shrinkage rate of the resin cements increased with increasing ceramic thickness. The cure speed by light cure was 15-322 times faster than by chemical cure. Significance. The polymerization shrinkage kinetics of dual-cured resin cements significantly differed between brands under various curing conditions. Clinicians should be aware of the setting characteristics of the cements, so they can choose the optimal materials for different clinical situations. (c) 2008 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.1