Relationships between dentin and enamel mineral at the dentino-enamel boundary: electron tomography and high-resolution transmission electron microscopy study.

To better understand the nature of the relationships between mineral phases at the dentino-enamel boundary (DEB), we performed electron tomography (ET) and high-resolution transmission electron microscopy (HR-TEM) of the apical portions of rat incisors. The ET studies of the DEB at the secretory stage of amelogenesis revealed that nascent enamel crystals are co-aligned and closely associated with dentin crystallites in the mineralized von Korff fibers, with the distances between dentin and enamel crystals in the nanometer range. We have further studied the relationships between dentin and enamel crystals using HR-TEM lattice imaging of the DEB. Among dozens of high-resolution micrographs taken from the DEB we were able to identify only one case of lattice continuity between dentin and enamel crystals, indicating direct epitaxy. In other cases, although there was no direct continuity between the crystalline lattices, power spectra analysis of lattice images revealed a very high level of co-alignment between dentin and enamel crystals. Hence, we propose here that the high degree of alignment and integration between dentin and enamel mineral can be established either by epitaxy or without direct interactions between crystalline lattices, probably via regulation of mineral formation and organization by integrated organic matrices of dentin and enamel at the DEB.