Distribution of capillaries in relation to the life cycle of odontoblasts in the rat incisor. The fate of the pulp at the incisal end.

Although the rat incisor is used widely in the study of dentinogenesis there is little information on the pulp capillaries and the fate of the pulp contents incisally. The capillaries have now been described in relation to the life cycle of the odontoblasts using light microscopy on perfusion fixed teeth and SEM on pulp vascular casts. Odontoblast precursors differentiated to preodontoblasts in the absence of local vessels. Capillaries entered the zone subjacent to preodontoblasts prior to their transformation to odontoblasts. They invaded the odontoblast layer after formation of odontoblast processes and during lengthening of their cell bodies. These capillaries formed a dense plexus which was separated from the predentine by about 10 micron thickness of odontoblast cytoplasm. Electron microscopy near the incisal end showed that the odontoblasts lost their processes and their polarity to form postodontoblasts. This coincided with the deposition of atubular collagenous tissue at the periphery of the pulp. Loss of fenestrations in the capillaries seemed to coincide with the diminution of odontoblast function. Odontoblastic capillaries were lost before the postodontoblasts became separated from one another. There was evidence of degenerating vessels, cells and extracellular debris near the incisal end. Light and transmission electron microscopical evidence from demineralised teeth was correlated with SEM evidence from anorganically prepared specimens and considered in relation to dynamic events at the incisal surface. Thus the pulp closure region was found to include a central zone of mineralised, moribund pulp cells and debris surrounded by atubular tissue.