Earliest enamel deposits of the rat incisor examined by electron microscopy, electron diffraction, and electron probe microanalysis

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Abstract
In order to describe initial events in enamel mineralization and to help characterize inorganic-organic interactions in this tissue, the earliest rod and interrod enamel in mandibular incisors from normal young adult (100 gm) rats, perfused with 100% ethylene glycol, has been studied by transmission electron microscopy, selected area electron diffraction, and high-spatial-resolution electron probe microanalysis. Diffraction and probe data were correlated precisely from the same extracellular regions of the tissue. Sites were examined progressively as a function of location (a) from the most recently deposited enamel adjacent to ameloblasts toward the dentin-enamel junction and (b) from the apical portion of the tooth longitudinally toward its incisal end. Electron diffraction patterns consistent with that of a poorly crystalline hydroxyapatite were generated at all locations. Diffraction characteristics changed only slightly toward that of more crystalline hydroxyapatite at different locations. Earliest apical enamel generated molar Ca/P ratios in a range of 0.99–1.46 (average 1.24 ± 0.15). Molar Ca/P ratios of the first enamel interrod elements increased from ∼1.24 at ameloblast-enamel boundaries to ∼1.40 at the dentin-enamel junction, small changes corresponding to those observed in electron diffraction characteristics.