Influence of viscosity and curing mode on degree of conversion of dual-cured resin cements

OBJECTIVE The purpose of this study was to evaluate the effects of the viscosities and curing modes on the degree of conversion (DC) of two resin cements. METHODS Eight experimental groups were evaluated (n=5), according to the dual-cured resin cements (Nexus 2/Variolink II), viscosity (low and high) and evaluation time (5 minutes and 24 hours). The resin cements were applied to surface of a horizontal attenuated-total-reflectance unit and were polymerized either with self-cure (SC) or light exposure (XL3000/3M ESPE) for 40 seconds. Infrared spectra were obtained after 5 minutes and 24 hours (Nicolet 520 FT-IR/Thermo Scientific Inc.). DC was calculated according to changes in aliphatic-to-aromatic peak ratios pre- and post-curing. Data (%) were analyzed by 3-way repeated measure ANOVA (curing mode, viscosity and time interval) and Tukey's post-hoc test (P<.05). RESULTS The dual-polymerizing mode provided higher DC than auto-polymerization. The DC mean values increased for both resin cements after 24 hours. The low-viscosity resin cements from light-activated or self-cured groups exhibited higher DC than high viscosity version. CONCLUSION The DC of resin cements was higher for the low viscosity version, following the light-polymerization and when were tested after 24 hours.