Characterization of progenitor cells in pulps of murine incisors.

The continuous growth of rodent incisors requires the presence of stem cells capable of generating ameloblasts and odontoblasts. While epithelial stem cells giving rise to ameloblasts have been well-characterized, cells giving rise to the odontoblasts in incisors have not been fully characterized. The goal of this study was to gain insight into the potential population in dental pulps of unerupted and erupted incisors that give rise to odontoblasts. We show that pulps from unerupted incisors contain a significant mesenchymal-stem-cell (MSC)-like population (cells expressing CD90+/CD45-, CD117+/CD45-, Sca-1+/CD45-) and few CD45+ cells. Our in vitro studies showed that these cells displayed extensive osteo-dentinogenic potential, but were unable to differentiate into chondrocytes and adipocytes. Dental pulps from erupted incisors displayed increased percentages of CD45+ and decreased percentages of cells expressing markers of an MSC-like population. Despite these differences, pulps from erupted incisors also displayed extensive osteo-dentinogenic potential and inability to differentiate into chondrocytes and adipocytes. These results provide evidence that continuous generation of odontoblasts and dentin on the labial and lingual sides of unerupted and erupted incisors is supported by a progenitor population and not multipotent MSCs in the dental pulp.