Fine structure of partially demineralized enamel

Abstract

Certain technical innovations were introduced in the fixation of enamel which improved the preservation of the matrix and aided in its visualization by electron microscopy. These were: 1. The use of reactive dyes as fixatives and stains of the protein matrix. 2. The use of formic acid in demincralization fixation. 3. Control of the ratio of tooth material to volume and concentration of acid used. The fine structure of enamel rods was examined in longitudinal and transverse orientation. In cross-section, adult enamel rods appeared arcade shaped with a projection extending between rods in subjacent layers. Deciduous enamel rods appeared as distinct circular units or incomplete rods separated by an extensive interrod area. Structural alterations contributing to the formation of striae of Retzius, Hunter-Schreger bands, striations, tufts, lamellae and caries were examined. Sections stained with phosphotungstic acid following partial demineralization revealed an organic substructure which appeared to differ in morphology with varying location in a single tooth or between different teeth. On the basis of contributory histochemical evidence of protein distribution and acid solubility, it was considered that micrographs accurately represented organic matrix in varying states of aggregation. Some difficulty in interpretation was encountered which may have resulted from loss of soluble protein, reprecipitation, blocking of reactive groups of protein by dehydrating and embedding media, and reaction of the embedding medium with phosphotungstic acid.