X-ray diffraction of enamel from human premolars several years after eruption

Small slices were cut from rods prepared from the labial surface of premolars extracted 4 and 5 years after eruption. Consecutive slices (200 microns thick) were taken at distances 500 microns apart from each other. X-ray diffractograms were obtained from each slice in a Guinier camera. Distinct reflections were obtained from slices up to depths of 2000 microns. The average depth of good cristallinity was 1000 microns in these older teeth in contrast to freshly erupted teeth where it is about 300 microns. No gradient could be detected in the lattice parameters from the surface layer towards the dentino-enamel junction in these older teeth. The average lattice parameters were a = 9.453 A and c = 6.890 A. Compared to data obtained on young teeth (Driessens et al., J. Biol. Buccale 10: 55, 1982) the crystallinity of the mineral appeared to increase with age in deeper layers. This result is consistent with the decrease of the caries susceptibility of human enamel with age postulated in the literature.