Influence of the crystal orientation in human enamel on its reactivity to acid as shown by high resolution microradiography

Abstract

High resolution microradiographs of 5μ thick ground sections of human dental enamel cut in various planes and treated with acids showed that the decalcification process in caries is indistinguishable from that of dissolution by acids. In both, the “head” and “tail” of the prism exhibited different reactivities, but the order of preference could be reversed simply by changing the direction of attack. Thus, when the attack progressed parallel to the prism lines the prism “heads” were most reactive and a honeycomb structure was produced. When the attack progressed perpendicular to the prism lines the prism “heads” were less reactive and a fibrous structure was produced. The effect is explained in terms of the crystal orientation within the enamel prisms and the probable anisotropy of chemical reactivity of the crystals, either inherent in the crystals or resulting from the presence of organic material around them.