Periodontal Ligament Cells Are Involved in the Formation of Intracanal Cementum-Like Tissue After Regenerative Endodontic Procedures: A Mouse in situ Model

Abstract

Regenerative endodontic cell-homing procedures are frequently performed on injured immature teeth diagnosed with pulp necrosis and/or apical periodontitis. The representative histological finding after those procedures is cementum-like tissues filling in the root canal but details of the healing process remain unknown. We investigated that healing process histologically using a mouse in situ model. Regenerative endodontic procedures were experimentally performed on noninfected maxillary first molars of 6-week-old male C57BL/6 mice, after which the healing process was investigated using histology and immunohistochemistry. Immediately after the regenerative endodontic cell-homing procedures, blood clots were seen in the root canals that disappeared over time. On day 7, the blot clot in the root canal was replaced by granulation tissue. From day 14 onward, cementum-like tissues were filled in the root canals, while the amount of fibrous tissue was reduced. Immunohistochemically, positive reactions for periostin were seen in the fibrous tissue in the root canal, the apex, and periodontal ligament cells. On the other hand, positive reactions for nestin were not detected in the root canal. CD31-positive cells with a luminal structure were also observed in the fibrous tissue around the apex and around the newly formed cementum-like tissues in the root canal. Thus, in this study, we have established an in situ mouse model of regenerative endodontic procedures. The results of this study suggest that periodontal ligament cells and vascular endothelial cells grow into the root canals from the apex, replace the blood clots, and participate in the formation of cementum-like tissues with angiogenesis during the healing process of regenerative endodontic procedures.

Dental Pulp Cell Transplantation Combined with Regenerative Endodontic Procedures Promotes Dentin Matrix Formation in Mature Mouse Molars

“…Another research group recently presented their findings on experimentation with REPs in immature mouse teeth [59]. Their data also demonstrated the feasibility of REPs in immature teeth from mice with open apexes, and their histological findings through H&E staining were similar to those obtained in the present work.…”

“…In this study, we demonstrated that an REP was achievable in mature mouse molars and that the local transplantation of DPCs improved the outcomes of REPs by promoting the formation of odontoblast-like cells and enhancing vasculogenesis. In terms of methodology, the procedure itself could be regarded as successful since REP and/or REP + DPC treatment led to new tissue formation inside the canals of mature mouse molars, similar to the healing responses observed in previous preclinical studies using the mature molars of larger animals [57,58] and immature mouse molars [59]. Furthermore, the lack of periapical lesions or root resorption in almost all samples in the µCT data supports this hypothesis.…”

“…The direct effect of MTA in the formation of the regenerated tissue was not assessed in the current study, however the absence of nestin immunoreactivity, less OPN staining in the REP group, in addition to the instrumentation of canals which would void canals of remaining pulp tissue, suggests that MTA did not induce by itself the appearance of odontoblast-like cells. Furthermore, Komada et al showed that REPs performed with MTA as a sealing material in immature molars did not lead to the formation of nestin immunoreactive cells [59]. While we cannot rule out that MTA influenced the differentiation of the transplanted cells, future studies can be performed to distinguish the contribution of MTA and the DPCs, for example using another material such as calcium hydroxide.…”