EPR properties of synthetic apatites, deorganified dentine, and enamel.

Electron paramagnetic resonance spectroscopy (EPR) was used to study synthetic hydroxyapatite and approximately 1, 2, and 6% synthetic carbonated apatites, deorganified dentine, and enamel. The carbonated apatites were synthesized by hydrolysis of dicalcium phosphate. Comparisons were made with spectra from enamel and deorganified dentine. Microwave power saturation and dose responses were determined for the synthetic materials. The Marquardt version of the Levenberg decomposition method was used to extract individual signals from the apatite data. Two samples of dentine were irradiated with 25 and 100 Gy, respectively, from a 60Co source. The first sample was then deorganified at 200 degreesC using the Soxhlet extraction technique. A third sample was irradiated with 100 Gy after deorganification. The resulting EPR spectra were then compared. It was determined that the dosimetric signal of 2% synthetic carbonated apatite was approximately the same as that of enamel. It was also verified that the dosimetric signal saturates at about 2% in synthetic carbonated apatites. The study established that the precenters responsible for the dosimetric signal (g perpendicular = 2.0018, g parallel = 1.9985) are preferentially concentrated in the surface-accessible region of the mineral component, as shown by the approximately 80% attenuation of the dosimetric signal in dentine following deorganification. The precenters responsible are not destroyed by the deorganification since the magnitude of the dosimetric signal from the dentine specimen irradiated following deorganification was approximately twice that of the comparable untreated, irradiated sample. Finally, the dose response of 2 and 6% synthetic carbonated apatites was determined.