γ- and UV-induced CO2- radicals in tooth enamel

Results of comparative EPR study of dental enamel powders and bulk samples irradiated by gamma-rays and by UV-light are reported. It is shown that the EPR spectra of UV- and gamma-irradiated powders have a similar shape, but different saturation behavior, which implies that these signals are different. Angular anisotropy of the EPR signals of enamel plates (bulk samples) irradiated by UV-light is considerably higher than for the gamma-irradiated ones. Annealing behavior of defects in irradiated enamel showed that both UV- and gamma-irradiation produce EPR signals primarily caused by the same paramagnetic species, namely oriented and disoriented CO2 radicals. It can be shown that for each type of irradiation the ratio between the amounts of these radicals is a fixed value. These values do not depend on the type of the enamel, nor on the irradiation dose in the range of 0.5-10 kGy. Differences in saturation curves for UV- and gamma-irradiated powdered samples as well as differences in anisotropy observed in bulk ones may be explained by different ratios of the two CO2 species. Thus, it is possible to define the type of the radiation to which the samples were exposed by measuring the anisotropy of the EPR spectra of dental enamel plates. (c) 2007 Elsevier Ltd. All rights reserved.