Electron spin resonance study of sound and carious enamel

The present electron spin resonance (ESR) study aimed to investigate chemical alterations in enamel apatite associated with carious attacks. Enamel blocks were cut from sound areas and natural white spot lesions of human molar teeth and then X-irradiated at room temperature in air. Q-band ESR analysis of these samples showed the presence of two stable signals in the spectra recorded at room temperature. One of them has been identified at CO3-(3) centers, which originate from the carbonate ion substituting in the apatite lattice. The other signal is tentatively identified as O- defects in the hexad axis of apatite lattice. A comparison of the spectra between sound and carious samples demonstrated that the intensity ratios between the O- and the g parallel component of CO3-(3), R = O-/CO3-(3) (g parallel), are significantly higher in the carious samples than in the sound ones. This suggests that enamel apatite in the white spot lesions may have less carbonate ions in the crystal lattice, or have a higher producibility of the O- defects in its hexad axis. The observed alterations in enamel apatite may well be accounted for by remineralization playing a major role in the formation of white spot lesions, because this acid-dissolution study using irradiated enamel blocks showed that the R values do not increase but decrease in a simple process of demineralization.