Differentiation capacity and maintenance of dental pulp stem/progenitor cells in the process of pulpal healing following tooth injuries

Recently, we demonstrated that a pulse of 5-bromo-2’-deoxyuridine (BrdU) given to prenatal animals discloses the existence of slow-cycling long-term label-retaining cells (LRCs), or putative adult stem/progenitor cells, which reside in the dental pulp. Using several tooth injury models such as cavity preparation, tooth replantation, tooth or tooth crown transplantation, and tooth germ transplantation, we have clarified the dynamics and differentiation capacity of LRCs postoperatively. Our recent studies have demonstrated that allogenic tooth transplantation may influence the maintenance of dental pulp stem/progenitor cells. Dense LRCs are competent to proliferate and differentiate into odontoblast-like cells after tooth injuries. In the case of tooth replantation and autogenic tooth transplantation, dense LRCs remain in the perivascular environment in the center of the dental pulp for a long period. In contrast, allograft LRCs disappear from this niche during postoperative weeks 2–4. The loss of LRCs, even in cases without immunological rejection, is attributed to the extensive apoptosis taking place in these cells, with the exception of newly differentiated odontoblast-like cells. Host and recipient interactions that occur with allografts disturb the maintenance of putative stem/progenitor cells, resulting in the disappearance of these cell types.