A light and electron microscopic study of the nearly mature enamel of rat incisors.

Abstract

AbstractThe structure of the organic matrix close to the mature enamel in 100 gm rat incisors was studied by light and electron microscopy using EDTA decalcified teeth.Under the light microscope, in 0.5 μ Epon sections, the enamel layer of cross sectioned upper incisors was about 60 μ thick. The inner enamel was about 40 μ thick and consisted of an initial enamel layer (4 μ) adjacent to the dentin in which no rod profiles were seen, and an inner layer proper which contained six to eight rows of oval‐shaped rod profiles set in a homogeneous background. The profiles in any given row were inclined mesially or laterally and alternated in adjacent rows. The outer enamel was about 20 μ thick and consisted of an outer enamel proper and a 2–4 μ thick final enamel layer which smoothed out the enamel surface. The outer enamel proper contained smaller elliptical rod profiles in a more abundant background. These profiles were not arranged in rows and were oriented at right angles to the enamel surface. The final enamel layer contained no rod profiles and was lined on its outer surface by a PA‐Schiff positive layer resembling a basement membrane.Under the electron microscope the matrix of rod profiles and interrod material could be distinguished. This consisted of aggregated tubular (and filamentous) subunits, 250 Å in diameter, with empty space between them. Within the rod profiles the subunits ran parallel to the rod's long axis, whereas in the interrod material the subunits were again parallel but but running at right angles to the subunits of the rods. In addition to forming the material between the rods, the interrod material also formed the initial and final enamel layers.