Influence of Tooth Maturity on Healing Outcomes in Regenerative Endodontics

Regenerative endodontic procedures using blood clots (BC-REP) for immature teeth typically exhibit a periodontal ligament–like healing pattern. However, a pulp-like healing pattern is observed in the presence of residual pulp. This study aimed to clarify the healing phenotype according to tooth maturity when performing BC-REP in the presence of residual pulp, focusing on migrated mesenchymal stem/stromal cells (MSCs). BC-REP rat molar models were created in the presence of residual pulp at ages corresponding to tooth developmental stages, from immature to mature (5 wk: immature, root is still growing; 8 wk: near mature, root has finished growing in length but the apex is not formed; 11 wk: mature, the apex is formed). The healing pattern and histological MSC markers (α–smooth muscle actin [α-SMA], CD73, CD90, and CD146) were investigated. The frequency of periodontal ligament–like healing was higher in mature teeth than in immature teeth. In addition, more healing macrophages were observed at the apical site 28 d after BC-REP, which is the final stage of healing. In immature teeth, double-immunopositive cells for proliferation markers (ki67 and proliferating cell nuclear antigen [PCNA]) and α-SMA were frequently observed in the vicinity of the root canal orifice 7 d after treatment, which is the early stage of healing. By contrast, in mature teeth, the number of CD73-, CD90-, and CD146-immunopositive cells increased at the apical site after 7 and 28 d. CD90- and CD146-immunopositive cells expressed cell proliferation markers (ki67 or PCNA) after 7 d. MSC migration after BC-REP likely varies based on tooth maturity, resulting in different healing phenotypes.