High-resolution electron-microscopic study of the relationship between human enamel and dentin crystals at the dentinoenamel junction

The development of dentin and of enamel share a common starting locus: the dentinoenamel junction (DEJ). In this study the relationship between enamel and dentin crystals has been investigated in order to highlight the guidin g or modulating role of the previously mineralized dentin layer during enam el formation. Observations were made with a high-resolution electron micros cope and, after digitalization, image-analysis software was used to obtain digital diffractograms of individual crystals. In general no direct epitaxi al growth of enamel crystals onto dentin crystals could be demonstrated. Th e absence of direct contact between the two kinds of crystals and the prese nce of amorphous areas within enamel particles at the junction with dentin crystals were always noted. Only in a few cases was the relationship betwee n enamel and dentin crystals observed, which suggested a preorganization of the enamel matrix influenced by the dentin surface structure. This could b e explained either by the existence of a proteinaceous continuum between en amel and dentin or by the orientation of enamel proteins by dentin crystals .