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.