Dentinogenic potential of human adult dental pulp cells during the extended primary culture

Despite the frequent use of primary dental pulp cells in dental regenerative research, few systematic studies of stemness for osteogenic and dentinogenic differentiation of human adult pulp cells have been reported. To investigate the stemness of human adult dental pulp cells, pulp tissues were obtained from extracted third molars and used as a source of pulp cells. In FACS analysis and immunophenotyping, the general mesenchymal stem cell markers CD44, CD90, and CD146 were highly expressed in early passages of the pulp cell culture. The stem cell population was dramatically decreased in an expansion culture of human dental pulp cells. When pulp cells were treated with additives such as beta-glycerophosphate, ascorbic acid, and dexamethasone, nodule formation was facilitated and mineralization occurred within 2 weeks. Expression of osteogenic markers such as alkaline phosphatase, osteocalcin, and osteonectin was relatively low in undifferentiated cells, but increased significantly under differentiation conditions in whole passages. Dentinogenic markers such as dentin sialophosphoprotein and dentin matrix protein-1 appeared to decrease in their expression with increasing passage number; however, peak levels of expression occurred at around passage 5. These data suggested that stem cells with differentiation potential might exist in the dental pulp primary culture, and that their phenotypes were changed during expansion culture over 8-9 passages. Under these conditions, a dentinogenic population of pulp cells occurred in limited early passages, whereas osteogenic cells occurred throughout the whole passage range.