EPR AND ENDOR OF RADIATION-INDUCED CO33- RADICALS IN HUMAN TOOTH ENAMEL HEATED AT 400-DEGREES-C

Upon irradiation human tooth enamel exhibits the well-known ''asymmetr ic EPR singlet near g = 2''. In recent years it has been convincingly demonstrated that the main radical contributing to this spectrum is CO 2- although EPR studies in the seventies very often erroneously claime d CO33- to be the dominant radical. In the meantime several types of C O33- radicals [carbonate replacing phosphate (B-site) or hydroxy group s (A-site)] have been identified in synthetic apatites prepared at hig h temperatures or in apatites precipitated from solution and dried at high temperature (typically 400 degrees C). In the present study human tooth enamel was heated at 400 degrees C and subsequently irradiated with X-rays at 77 K. It is shown that warming up to about 150 K yields a simple isolated CO33- spectrum with contributions from exactly the same two radicals identified in synthetic apatites. Under certain cond itions strong spectra from phosphate derived radicals are present. The CO2- signal which is dominant after room temperature irradiation of u nheated enamel is very weak, however gaining importance after storing the low temperature irradiated sample at room temperature. Also ENDOR results supporting the CO33- identification are presented.