The presence of pericytes and transitional cells in the vasculature of thehuman dental pulp: An ultrastructural study

The aim of this study was to determine the ultrastructural characteristics of the microvasculature of healthy human dental pulp, with particular refer ence to pericytes. Pulp tissue was taken from healthy impacted third molars following extraction. Eight teeth were obtained from 17- to 25-year-old pa tients and pulp tissue was processed for examination using standard techniq ues for transmission electron microscopy. The pulp was rich in capillaries composed of endothelial and peri-endothelial cells in a 4 : 1 ratio. Endoth elial cells contained typical and abundant Weibel-Palade bodies. Three type s of peri-endothelial cells were identified: pericytes, transitional cells and fibroblasts. Pericytes were embedded within the capillary basement memb rane. Transitional cells were partly surrounded by basement membrane, but s eparated from the endothelium by collagen fibrils; fibroblasts were outside , but adjacent to the basement membrane and closely associated with collage n fibrils. Pericytes and transitional cells, but not peri-endothelial fibro blasts, contained low numbers of dense bodies similar to the endothelial We ibel-Palade bodies. Our observations are consistent with the hypothesis tha t, during normal tissue turnover, some pericytes may originate from endothe lium and migrate away from the vessel wall to undergo transition to a fibro blastic phenotype.