The mechanism of CO2- radical formation in biological and synthetic apatites.

Biological apatites (tooth enamel, bone) and their synthetic analogues were exposed to gamma rays, UV light, or thermal treatment and studied by electron paramagnetic resonance (EPR). The thermal generation of CO2- radicals in synthetic apatite was observed for the first time. It was shown that the experimental EPR spectra of all of the above-mentioned materials are caused by the contribution of two types of CO2- radicals: axial and orthorhombic.

Separation of the contributions from gamma- and UV-radiation to the EPR spectra of tooth enamel plates.

Anisotropy of EPR spectra of tooth enamel plates irradiated with gamma-rays and UV light has been studied. UV-irradiated enamel plates exhibit a stronger anisotropy than gamma-irradiated plates. Investigation of samples cut out of different teeth and irradiated to different doses showed that the value of anisotropy is characteristic of each type of irradiation; it equals to approximately 0.

13C hyperfine interactions of CO2- in irradiated tooth enamel as studied by EPR.

The EPR spectrum of tooth enamel caused by 13C hyperfine interactions of the CO2- radical were studied on gamma-irradiated powdered samples annealed for 40 min at different temperatures up to 250 degrees C. The lineshape and hyperfine splitting of the spectra were found to depend on the annealing temperature. Experimental spectra were compared with calculated ones assuming that EPR spectra are formed by two CO2- species--axial (rotating) and orthorhombic (braked) radicals.