A magnetic resonance spin label study of human dental enamel.

The rotational mobility of nitroxide spin labels in human dental enamel indicates that the regions accessible to the largest label used were of the order of 15 Å (1.5nm). The nitroxide coupling constants were used to determine the degree of label-solvent replacement. Calibration of the microwave cavity Q with liquid water samples indicate that about 2.3 per cent by weight of the enamel samples was liquid water. 55, 50 and 23 per cent of this liquid water appeared to be removed by vacuum-drying or equilibration with ethanol or benzene, respectively. Decay of the radical species was observed; the mechanism of reduction of the labels is unknown but use of a model of diffusion with simple first order decay allowed the calculation of an apparent diffusion constant D of 6 × 10^?9cm²/s (6 × 10⁵nm²/s) at 22 °C.