Thermal Analysis on the Cure Speed of Dual Cured Resin Cements Under Porcelain Inlays

The reaction kinetics of five commercial dual cured resin cements (Bistite, Dual, Scotchbond, Duolink and Duo) were investigated when cured under varying thicknesses of porcelain inlays by chemical or light activation. The effect of the porcelain disc on the rate of polymerization of dual cured resin cement during light exposure was evaluated using thermal analysis, thermogravimetric analysis and differential scanning calorimetry. Inorganic filler weight %, the heat of cure (Delta H), the maximum rate of heat output and the peak heat flow time were measured when the polymerization reaction occurred by chemical cure only or by light exposure through 1, 2 and 4-mm thick porcelain discs. In 4-mm thick porcelain discs, the exposure time was varied from 40 to 60 s to investigate the effect of the exposure time on polymerization reaction. Cure speed by light exposure was 5--20 times faster than by chemical cure. The dual cured resin cements differed markedly in their sensitivity to light and chemical activation. The peak heat flow time increased by 1.51, 1.87 and 3.24 times as light cure was carried out through 1, 2 and 4-mm thick porcelain discs, respectively. Exposure times recommended by the manufacturers were insufficient to compensate for the attenuation of light by the 4-mm thick porcelain disc.