Electron-Nuclear Double Resonance of Human Tooth Enamel Heated at 400°C

Abstract.

Powdered tooth enamel heated at 400°C has been examined with electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR), and ENDOR-induced EPR (EIEPR) methods and compared with hydroxyapatite synthesized at high temperature. The EPR spectrum of the tooth enamel sample consists mainly of signals assigned to O⁻ and CO₂ ⁻ radicals, in contradistinction to the synthetic apatite sample, where signals of O⁻ and CO₃ ³⁻ were detected. The ENDOR results of heated enamel show that the O⁻ radical is located at an A site and interacts with three unequivalent sets of ³¹P nuclei and two unequivalent protons. This supports the model proposed for synthetic apatite. The EIEPR results show that the ³¹P and ¹H ENDOR resonances originate from both O⁻ and CO₂ ⁻ radicals and that the ²³Na and ¹⁹F resonances originate only from a CO₂ ⁻ radical located probably at the surface.