Electron Microscopic Studies on the Organic Matrix of Enamel and Dentin

In previously published electron microscopic studies on the organic substance of enamel, the organic matrix was depicted in thin sections as a meshwork of delicate fibrils.1'"i " If one compares these structures with photographs obtained by the replica method using mineralized enamel, the original relationship between the organic and the inorganic components of the enamel is difficult to reconstruct. In the decalcified thin section one sees the organic meshwork with interlacing fibrils running in all directions in a disorderly fashion. In the replica method, in contrast, the rod-like crystals of hydroxyapatite are regularly oriented within each prism. The crystals do not fit into the meshes of the fibrillar lacework. Apparently, the method of decalcification accounts for changes in the organic structures which do not permit one to consider these meshworks as the true image of the organic substance. Other structures occurring in enamel have likewise been subjected to widely differing interpretations in electron microscopic studies. Several authors"2' have described an interprismatic substance (confirming, in a way, findings obtained by light microscopy), whereas others1"'5 have denied the existence of an interprismatic substance. In an attempt to clarify these problems the present study has been undertaken, using toothbuds. We expected to obtain information on the structure of enamel more easily from pre-enamel, young enamel, and from the ameloblast layer, since it is possible to prepare thin sections of these structures without decalcification. It has been previously assumed that there is an intercellular substance between the individual ameloblasts from which the interprismatic substance supposedly develops, the ameloblasts themselves giving rise to the prisms.7'0 Our investigations have led to different conclusions. Sections