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

Results of comparative EPR study of dental enamel powders and bulk samples irradiated by γ-rays and by UV-light are reported. It is shown that the EPR spectra of UV- and γ-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 γ-irradiated ones. Annealing behavior of defects in irradiated enamel showed that both UV- and γ-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 γ-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.