ADULT HUMAN ENAMEL - AN ELECTRON MICROSCOPIC STUDY OF CRYSTALLITE SIZE AND MORPHOLOGY

An electron microscopic study of thin sections from comminuted permanent human enamel was conducted to determine crystallite size and morphology. It was found that the mean thickness and width values for crystallites with an electron-opaque line are essentially the same as crystallites within the same aggregates but without the opaque line. The values obtained were considerably larger than those observed for developing human enamel, but only slightly larger than values previously reported for hypomineralized material (amelogenesis imperfecta). Cross-cut crystallites observed in this study were roughly flattened hexagons. Some of the variations include rounded rather than hexagonal poles and irregular interlocking surfaces. The size and shapes of cross-cut crystallites indicate that crystal growth assumes the directions necessary to fill the available space. The electron-opaque line reported by others was observed in 20% of the cross-cut crystallites. This finding in conjunction with the wide degree of rotation about the long axis may account for the low number of these electron-dense lines demonstrated in longitudinally cut profiles. © 1968 Academic Press Inc.