FORMATION OF DIFFERENTIATED TISSUES IN-VIVO BY PERIODONTAL CELL-POPULATIONS CULTURED IN-VITRO

The periodontium contains heterogeneous mesenchymal cell populations w ith various differentiation potentials. The capacity of these cells fo r tissue formation as well as the origin of their precursors are still not entirely defined. In this study, cells originating from different periodontal tissues were cultured in vitro, and tissue formation in v ivo following orthotopic re-implantation was investigated. Cells were recovered from the alveolar bone and periodontal ligament tissue of si x minipigs, and cultured cells were then grown on extracted dental roo ts from the homologous animals by means of co-culture in vitro. Each m inipig received 2 roots covered with alveolar bone cells, 2 roots cove red with periodontal ligament cells, and 2 control roots (without cell s) implanted into palatal bone defects. Intravital fluorochrome labeli ng was performed, and two minipigs were histologically examined after 2, 4, and 12 weeks in each case. Controls showed widespread resorption and ankylosis, whereas roots covered with cultured periodontal cells exhibited tissue formation in vivo. Alveolar bone cells synthesized a calcified cellular tissue resembling cellular cementum, suggesting tha t cells within this population might differentiate into cementoblasts when reimplanted with a dental substrate in vivo. Periodontal ligament cells exhibited no calcified tissue formation in vivo, but cells synt hesized a connective tissue with orientated fiber bundles attached to both host bone and root, resembling periodontal ligament. Results indi cate that cultured cells retain the capacity to form differentiated pe riodontal tissues after re-implantation, depending on the cells' origi n. Our findings also suggest that the alveolar bone contains cementoge nic precursors with the potential to differentiate into active cemento blasts in the presence of a dental substrate.