Spectral spatial electron paramagnetic resonance imaging as a tool to study photoactive dimethacrylate-based dental resins.

Photopolymerizable dimethacrylate-based dental resins, which are widely used in the current routine dental practice, show a very strong EPR signal. This signal has already been studied by EPR spectroscopy, but not by EPR imaging. The spectrum is quite complex due to hyperfine splitting and to the presence of two radical species, which is a priori not favorable to EPR imaging. In this work, the robustness of EPR imaging was investigated, both in the spatial and spectral-spatial modes, to characterize this type of material using small resin samples. The images produced using standard deconvolution and filtered backprojection procedure did not display any noticeable artifact. They also reflected the expected density of free radicals in two types of resin, photopolymerized with two different light irradiances. Moreover, the spectral-spatial imaging mode provided a complete spectrum for each pixel, which enabled to delineate the different distributions of the two radical species inside the samples. EPR imaging offered a different information compared to the usual degree of conversion measured by Raman spectrometry. These results suggest that EPR imaging could be used as a complementary tool to further characterize the dimethacrylate-based resins used in dental practice or for other applications.