Impact of Chemical Activation on Polymerization of Dual-Cured Resin

Objectives: This study investigated the impact of the chemical activation and the effect of delaying the light exposure on the polymerization kinetics and rate of a model dual-cured resin. Methods: The experimental material was formulated using purified monomers, and two mixtures were obtained: Base resin (BR) – Bis-GMA (50wt%), TEGDMA (50wt%), camphorquinone (0.8wt%), dimethyl-p-toluidine (2.5wt%) and hydroquinone (0.15wt%); Catalyst resin (CR) – Bis-GMA (50wt%), Bis-EMA4 (50wt%), benzoyl peroxide (2.5wt%) and hydroquinone (0.15wt%). The following groups were tested: [G1] immediate photo-activation after mixing BR+CR, using energy dose of 8J/cm²; [G2] similar to G1, using 16J/cm²; [G3] photo-activation 10min after mixing BR+CR, using 8J/cm²; [G4] similar to G3, using 16J/cm²; [G5] chemically-activated control. Photo-activation was conducted using a halogen curing device (XL3000; 400mW/cm²). Polymerization kinetics was evaluated in real-time, for 30min, using infrared spectroscopy with an attenuated total reflectance device (1scan/s, 8cm-1 resolution). Degree of conversion (DC) was evaluated at each second considering the intensity of C=C stretching vibration (peak height) at 1635cm^-1 and the symmetric ring stretching at 1608cm^-1, from polymerized and unpolymerized samples. Conversion rates (Rp) were calculated and the Rp^max values registered. Results: Final DC values (%) were 61.8, 71.1, 71.9, 69.1 and 56.1, for G1–G5, respectively, and Rp^max values were 24.4, 28.1, 10.5, 12.3 and 9.5. The chemical activation increased the final DC, but was insufficient to compensate for the lower energy dose. The dose influenced the final DC; for the higher dose, the chemical activation effect was less evident. The ED procedure increased the final DC for the lower dose, and reduced the Rp^max values for all conditions. Conclusions: The impact of chemical activation was dependent on the energy dose and the time that photo-activation was performed.

This study was supported by CNPq/Brazil (Grant 140233/2007-5).