Objectives: To evaluate the effectiveness of sodium sulfinate salt co-initiators on the degree of conversion (DC) of dual-cured cementing systems [combination of bonding agent (BA) and resin cement (RC)] when the activating light is attenuated or not available.
Methods: Two 5th generation products [Prime&Bond NT Dual-Cure/Calibra (Dentsply), and Excite DSC/Variolink II (Ivoclar/Vivadent)] were applied, either with or without co-initiators (sodium sulfinate salts) added to the bonding agents, to the surface of a horizontal attenuated-total-reflectance unit, and were polymerized using one of four conditions: self-cure (SC), or direct light exposure (DLE/XL3000/3M) through a glass slide or through pre-cured resin discs (shades A2 or A4/2mm-thick) (Z250/3M-ESPE). Real-time infrared spectra were obtained after placing components (uncured) and during 10 min (cured) (16 scans at 2 cm(-1), FTS-40/Digilab/Bio-Rad) to obtain polymerization kinetics. DC and maximum rate of polymerization (Rpmax) were calculated using standard techniques of observing changes in aliphatic-to-aromatic peak ratios pre- and post-curing. Data (n=5) were analyzed by two-way ANOVA and Tukey's test (p=0.05).
Results: The addition of co-initiators increased the DC in most of the groups. No significant difference in DC was observed between Prime Bond NT Dual-Cure/Calibra and its version without co-initiator using the DLE curing mode. All DLE groups exhibited the highest DC after 10 min. No significant difference in DC was observed between A2 and A4 pre-cured overlay groups. The SC groups exhibited lower DC than the light-activated groups regardless of the presence of co-initiator. Use of co-initiators increased the Rpmax only in the SC groups. The A2 and A4 groups exhibited lower Rpmax than DLE groups, regardless of the presence of co-initiator.
Conclusion: The detrimental effects of light attenuation on the DC were not avoided by inclusion of sodium sulfinate salts, despite their ability to eliminate the chemical incompatibility between acidic monomers and self-curing components.