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.