Structural relationships in the human odontoblast layer, as demonstrated by freeze-fracture electron microscopy

Abstract

The structural relationships in the odontoblastic cell layer of fully developed permanent human teeth were studied with the freeze-fracture technique. A good three-dimensional comprehension of the spatial arrangement of the cells was obtained. The odontoblasts displayed three types of membrane specializations. At the apical part, spot desmosomes (macula adherens) were abundant. Numerous gap junctions (nexuses) were distributed all over the cells. Tight junctions (zonula occludens) were found apically on the odontoblasts in some teeth. Between the tightly packed odontoblasts, fibers with a diameter of 0.1 to 1.0 μm were seen running through the cell layer. The true nature of these cell processes could not be established, but one group of them had features (shape and diameter) in common with unmyelinated nerve fibers previously described. Such fine caliber fibers regularly formed morphological contacts (gap junctions) with the odontoblasts. Fibrillar structures of the so-called von Korff type between odontoblasts were not observed. The odontoblasts were also seen to be in close contact with the subodontoblastic fibroblasts via gap junctions and desmosomes.