Post-polymerization reactivity of free radicals trapped in resin-based dental restorative materials by ESR spectroscopy

The propagating and allylic free radicals generated when polymerizing dimethacrylate resin-based materials used in dentistry are detected by electron spin resonance (ESR) spectroscopy as a nine-line spectrum. This study aimed to probe their post-polymerization reactivity with a novel methodology to quantify these radicals separately. X-band ESR spectra were recorded from a photo-cure dental resin composite (~ 20 days) and a dual-cure resin cement (~ 15 days). Spectra simulations were applied to separate and determinate the contribution from each radical to the ESR signal according to the method presented. The decay curves of the free radicals were then obtained to probe their post-polymerization reactivity as function of composition and initiation mode (photo-cure and self-cure). The allylic radical’s post-polymerization half-life time was approximately twice than that of the propagating radical, independently the composition and the activation mode, indicating that their relative reactivity does not depend of these parameters. The methodology presented for individual quantification of free radicals showed to be adequate to probe the kinetics of the free radicals generated and trapped in resin-based dental.