Abstract
Human dental enamel is composed 98% by weight of small, densely packed carbonated hydroxyapatite (HAP) crystals. These crystals have an unusual morphology and often contain a “central dark line” (CDL) defect. The HAP crystals in carious enamel are preferentially dissolved at the CDL defect. Bres et al. have identified three types of disorder in human tooth enamel crystallites near to the crystal midline: a) regions of lattice buckling and departure from hexagonal symmetry, b) dislocations and c) grain and twin boundaries. Nelson et al. have obtained very clear images of planar defects, similar to the CDL defects in human enamel, at the centers of crystals of certain synthetic carbonated apatites. In this present study HRTEM images have been obtained from carious regions of tooth enamel, and an analysis of the results is attemped in the light of previous work.
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