A Multifrequency (X-, Q-, and W-band) EPR and DFT Study of a Photopolymerizable Dental Resin

The free radicals generated during the polymerization process of Z100 (3 M ESPE) dental resin were examined by electron paramagnetic resonance (EPR) in X-, Q- and W-bands. Experimental generation and spectra simulations were associated with density functional theory (DFT) calculations to determine the molecular structure and explain the EPR spectrum formation. It was assumed that the EPR spectrum was formed by the sum of two different types of radicals: “propagating” and allylic. The spectra simulations and DFT calculations showed good agreement, indicating that the proposed model fully explained the nine lines of the EPR spectrum in X-band and showed that the spectrum formation is the sum of “9 + 5” lines, rather than the “5 + 4” lines predicted early. Simulations in Q- and W-bands showed very close correlation and were essential to support the proposed model.