Immunohistochemical and Histochemical Analysis of Newly Formed Tissues in Root Canal Space Transplanted with Dental Pulp Stem Cells Plus Platelet-rich Plasma

Introduction: Tissue regeneration in root canals after pulpectomy can be achieved by transplantation of autologous dental pulp stem cells and/or platelet-rich plasma. However, the identity of the newly formed tissue in the pulp; space has been only examined by histologic analysis. This study aimed to apply immunohistochemistry and histochemistry to detect specific markers in the newly generated tissues after root canal regenerative treatment. Methods: In our previous study, 32 root canals in 4 mature dogs were treated with a 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 to detect periodontal ligament tissue, nestin and dentin sialoprotein for odontoblasts, and bone sialoprotein and osteocalcin for bone tissues. Samples were also stained for tartrate-resistant acid phosphatase (TRAP) as a marker for osteoclastic lineages. Results: Continuous periostin-positive tissue was observed extending from the periodontal ligament into the inner canal surface in which the mineral islands were surrounded by weak periostin staining. There was also positive staining for TRAP, bone sialoprotein, and osteocalcin in the canal space, suggesting the presence of bone tissue. A layer of mineralized tissue along the inner surface of the root canal was negative for TRAP, suggesting the tissue likely to be cementum. In all samples, no nestin-positive reaction was observed, whereas dentin sialoprotein was detected in PDL, dentinal tubules, and intracanal fibrous tissues. There was no difference between any of the 4 groups. Conclusions: The tissues formed in the dog mature root canals after regenerative endodontic procedures are not pulp tissues but mainly periodontal tissues.