The extent of the human odontoblast process as determined by transmission electron microscopy: the hypothesis of a retractable suspensor system.

Abstract

After fixation of fully formed human permanent teeth in liquid nitrogen the extent of the odontoblast process has been studied in transmission electron microscopy. The odontoblast process, limited by a trilaminar plasma membrane, was found just under the dentine-enamel junction. In cross section, the cytoplasm contained a granular mass with light and/or dense core granules. Bare unmyelinated nerve-like fibrils were seen in close connection with the odontoblast process. In the periodontoblastic space non calcified collagen fibrils were occasionally present. Cytoplasmic globules and granules limited by a trilaminar membrane, with occasional myelinic figures were also noted in the peripheral tubular lumens. The hypothesis of a retractable suspensor system is advanced to explain why in normal fixation conditions the odontoblast processes associated with nerve fibrils have not been observed in the outer layers of dentine.