Degree of conversion of dual-cured composite luting agents: The effect of transition metal-based touch-cure activators

Purpose: The aim of the study was (a) to assess the effect of universal adhesives and tooth primers with novel touch -cure activators on the conversion of dual -cured resin composite luting agents (RLAs) polymerized under the self -curing mode, and (b) to investigate the source of the catalytic effect exerted by the activators. Materials and Methods: The materials selected were the adhesive RLAs Panavia V5/Tooth Primer (PV5/TP5), Variolink Esthetic DC/Adhese Universal DC (VLE/ADC), and the self-adhesive RLAs GCem ONE/AE Primer (GCO/AEP), RelyX Universal/Scotchbond Universal Plus (RXU/SUP) and Panavia SA Universal/Clearfil Universal Bond Quick (PSU/CUQ), the later serving as a control with an aryl-sulfinate activator. Coronal dentin specimens were prepared ( n = 5/material), treated with the corresponding primers/adhesives (non -irradiated) and covered with a 100 mu m-thick RLA layer (SC+A group). Three specimen series were additionally prepared ( n = 3 x 5/material): A self -cured without the primers/adhesives (SC group), a dual -cured (20 s irradiation) with the corresponding primers/adhesives (DC+A group) and a dual -cured without primers/adhesives (DC group). All specimens were stored for 15 min (37 degrees C/dark/60 %RH). After demolding the degree of C = C conversion (DC%, top RLA surfaces) was measured by ATR-FTIR spectroscopy. The primer/adhesive liquids were further analyzed by ICP-MS and the microbrush tips of ADC by SEM-EDS. Results: The touch -cure activators increased the DC% in all self -cured RLAs but failed to reach the values of the corresponding dual -cured RLAs. The effect of the activators in dual -cured specimens was negligible. The ICP-MS analysis showed the presence of V (AEP, TP5, ADC) and Cu (SUP) transitional metals in the activators, with V been located at the free ends of ADC tip bristles. The V activators demonstrated the highest DC% improvement in self -cured specimens. Conclusion: The new touch -cure activators significantly increased the conversion of the self -cured RLAs. Therefore, this step should be considered as universally applicable and not selective, as currently proposed for the selfadhesive luting agents by the manufacturers.