Morphological and structural studies of early mineral formation in enamel of rat incisors by electron spectroscopic imaging (ESI) and electron spectroscopic diffraction (ESD).

Morphological and structural analysis of the earliest stage of crystal formation in enamel of rat incisors, by use of energy filtering transmission electron microscopy (EFTEM), has shown needlelike crystallites with a dotlike substructure. We conclude that these dots (nanometer-sized particles) have developed at nucleating, active sites along the non-collagenous matrix proteins in enamel. Calcium and phosphate groups are bound at such "active sites" and develop to nuclei, which grow to these stable dots (nanometer-sized particles). The dots coalesce rapidly in longitudinal direction, along the matrix proteins, with neighbouring dots to form parallel arranged "needlelike" crystallites. These needles grow and coalesce in lateral directions to ribbon-platelike crystallites. In enamel most of the organic substance becomes decomposed and transported to the ameloblasts. Consequently, the ribbon-platelike crystallites can coalesce to form much thicker (hydroxy)-apatite crystals than in dentine. Already in the earliest stage of crystal formation the mineral chains of dots (nanometer-sized particles) and the needlelike crystallites show a parallel orientation in the direction of the c-axis of hydroxyapatite. This is supported by the texture of the 002 reflections in the corresponding electron spectroscopic diffraction patterns (ESD), which appear as the first Bragg reflections.