Physicochemical properties of experimental composites light-cured with different radiant exposures

Objectives: The aim of this study was to evaluate the effect of different radiant exposures (REs) on physicochemical properties of experimental resin cements (ERCs) containing different concentrations of diphenyliodonium hexafluorophosphate (DPI-PF6) salt.
Methods: Four ERCs were prepared using a Bis-GMA/TEGDMA (1:1 molar ratio) base compound with a 60% mass fraction of silanated glass fillers. The ternary photoinitiator system was composed by 1 mol% of camphorquinone, 2 mol% of dimethylaminoethyl methacrylate and different concentrations of DPI-PF6: 0 (control), 0.5, 1 or 2 mol%. Near IR was used to assess degree of conversion (DC) in real-time in disc shaped-specimens (n=3) of 10 mm in diameter and 0.8 mm of thickness. Polymerization stress (PS) was measured using the Bioman (n=5) with 0.5 mm thick specimens (Watts, 2005). ERCs were light cured through an IPS E.max Press ceramic block (10 mm in length x10 mm in wide x 3 mm in thickness) by a LED source using 15, 30 and 60 J/cm² RE. Data were analyzed using two-way ANOVA/Tukey test at a significance level of 5%.
Results: The DC for a given DPI-PF6 concentration statistically increased with each increment of RE. Above 0.5 mol% DPI-PF6, DC values were similar for a given RE applied. At 0 mol% DPI-PF6, DC was statistically lower within the same RE compared to the other DPI-PF6 concentrations. In general terms, the PS values above 0.5 mol% DPI-PF6 were all statistically similar, but greater than the ones presented by 0 mol% DPI-PF6 materials. This is explained by the DC values registered
Conclusions: The addition of at least 0.5 mol% of DPI-PF6 improved conversion of the ERC for all energy levels. At 60 J/cm², for all DPI-PF6 concentrations, conversion was statistically improved. However, the addition of DPI-PF6 led to increased values of stress for all energy levels.