Microradiographic and microhardness studies of developing enamel

Abstract

This study was undertaken on human and Rhesus monkey enamel using three methods of analysis to gain information concerning the pattern of enamel calcification: (1) microhardness pattern of enamel mineralization; (2) microradiography; and (3) plastic substitution studies. Halves of teeth were selected and tested on a Tukon Microhardness Tester with a Knoop Diamond Indentor. The other half of each tooth was further sectioned. Several sections from each tooth were ground to less than 150 [mu] in thickness and microradiographs were taken; the remainder were used for the substitution studies. All organic tissue and water were removed from the sections and replaced with plastic. Decalcification of these sections revealed areas of low and high organic and water content. It was found that mineralization of the enamel matrix begins at the dentino-enamel junction and proceeds peripherally, thus following the incremental pattern of formation of the enamel matrix. Final calcification is completed after the matrix is completely deposited and follows this same pattern from the dentino-enamel junction peripherally. The enamel rod matrix becomes calcified before the interrod substance, the latter thus presenting pathways for diffusion of tissue fluid containing calcium and phosphate ions, during the mineralization process. The interrod substance is the first area of enamel to be altered in dental caries. Thus the steps in enamel destruction are in reverse order to those in enamel formation.