Fig. 5.

Dental stem cell heterogeneity in adult mouse incisors. (A) The current model posits that stem cells (red) in the outer enamel epithelium (OEE) give rise to transit-amplifying (TA) cells (green) and stratum intermedium (SI) cells (pink) in the inner enamel epithelium (IEE), which then differentiate into ameloblasts (AMB; blue). (B) However, we now know that, during homeostasis, actively cycling IEE cells (green) contribute to the formation of both the enamel-producing ameloblasts (blue) and the adjacent non-ameloblast epithelial cells (red). During injury repair, additional progenitors enter the cell cycle (green), and SI cells (pink) can also convert to differentiate into ameloblasts (blue). (A and B adapted from Sharir et al., 2019.) (C) Different types of cells have also been shown to function as stem cells in the dental mesenchyme. These include glial cells (yellow) and pericytes (blue). They reside in the neurovascular bundle (NVB) niche, giving rise to cells in the fast-cycling regions at both the labial and lingual sides to support the rapid turnover of incisor mesenchymal cells (red arrows). laCL, labial cervical loop; liCL, lingual cervical loop; ODB, odontoblasts; SR, stellate reticulum.