A Rat Model for Autotransplantation of Mature Molars: An Exploratory Histological Assessment of Root-End Resection

Autotransplantation of mature teeth is often complicated by pulp necrosis due to compromised blood supply. This study aimed to establish a reproducible rat model for mature molar autotransplantation and to explore, within this model, the histological effects of root-end resection (RER).

In rats, the maxillary third molar (M3) was autotransplanted into the socket of the extracted second molar (M2). Animals were randomly allocated to a control group (direct transplantation) or an RER group (transplantation following apical third root resection). Tooth positioning and structural integrity were assessed using micro-computed tomography (micro-CT). At 4 weeks postoperatively, pulp and periodontal tissues were evaluated by haematoxylin and eosin (H&E) staining, and vascular-associated markers were examined using CD31/α-SMA dual immunofluorescence.

The recipient M2 socket was significantly larger than the donor M3 (p < 0.05), allowing stable placement of the transplanted tooth. No significant differences were observed between groups in transplantation success rate (75.0% Control vs. 70.0% RER), operative time, or extra-oral time (p > 0.05). H&E staining demonstrated extensive pulp necrosis in the control group, whereas the RER group showed ingrowth of vascularized connective tissue and cementum-like tissue formation. Immunofluorescence revealed sparse CD31/α-SMA-positive signals in controls and limited apical signals in the RER group, with a significantly greater double-positive area in the latter (p < 0.001).

A stable and reproducible rat model for autotransplantation of mature molars was successfully established. Within the constraints of this model, RER was associated with early histological features suggestive of vascular ingrowth. Further studies are required to determine the biological significance and clinical relevance of these observations.