Structure of mature human dental enamel as observed by electron microscopy

Abstract

The ultrastructure of mature human dental enamel was studied by direct electron microscopy of ultrathin sections cut with a diamond knife and of replicas made from lightly etched cut surfaces. The enamel prisms were found to resemble keyholes when cut in cross-section, with the prisms measuring about 5 μ in dia. across the heads of the keyholes and about 9 μ in height over the extreme head to tail dimensions. The prisms were found to be oriented so that the heads of the prism cross-sections were directed cuspally and the tails were directed cervically. The crystallite orientation within any single prism was characterized by being coaxial with the prism in the extreme head region of the prism, but tipped more and more away from the prism axis in moving towards the tail of the prism. This orientation of crystallites in prisms was observed regardless of the plane of sectioning used to obtain a sample for observation. There was no evidence for an “interprismatic substance” between the prisms. Three-dimensional plastic models were prepared based on an idealized representation of enamel structure and sectioned for comparison with the electron micrographs. All structures observed in the micrographs could be simulated by sectioning the models in the proper planes.