Method: In our previous study, 32 root canals in four mature dogs were treated with pulp regeneration procedure after pulpectomy using either blood clot, transplantation of dental pulp stem cells, platelet-rich plasma, or a combination of cells and plasma. In the present study, the tissues were examined for the expression of periostin and nestin that serve as markers for periodontal ligament tissues and odontoblasts, respectively. Samples were also stained for tartrate-resistant acid phosphatase (TRAP) as a marker for osteoclastic lineages.
Result: Continuous periostin-positive tissue was observed extending from the periodontal ligament into the inner canal surface. Mineral islands in the canal space were surrounded by weakly positive periostin staining and there were strongly stained TRAP positive cells, suggesting the presence of bone tissue. A layer of mineralized tissue along the inner surface of the root canal was TRAP-negative, which was likely to be cementum tissue. In all samples, no nestin-positive reaction was found. There was no difference between any of the four groups.
Conclusion: The tissues formed in the mature root canals after regenerative endodontic procedures are not pulp tissues but mainly periodontal tissues.