Abstract: PURPOSE: To evaluate the impact of impacted lower third molar(ILTM) extraction by root dislocation first method on bone formation in the distal middle of the second molar(M2M), pulp status and external root resorption (ERR). METHODS: A total of 64 patients who underwent ILTM extraction in the First Affiliated Hospital of Xinjiang Medical University from January 2023 to October 2023 were selected. Among them, 32 patients underwent root first removal of ILTM (experimental group), and 32 patients underwent crown first removal of ILTM (control group). Preoperative and postoperative M2M mobility, pulp status, ERR situation, and postoperative visual analog scale for pain were recorded. Cone-beam CT was performed at 3 and 6 months after operation to measure bone defect depth of M2M, bone height of M2M, percentage of bone height, and bone ash degree. SPSS 26.0 software package was used for data analysis. RESULTS: The VAS pain score of the experimental group on the third postoperative day was significantly lower than that of the control group (P<0.05), while there was no significant difference in surgical time, M2M pulp vitality, and mobility between the two groups(P>0.05); the amount of bone resection in the experimental group was significantly less than that in the control group (P<0.05). The immediate postoperative near-midfacial and distal tongue-side probing depth (PD) in the experimental group was significantly lower than that in the control group(P<0.05). At 3 and 6 months postoperatively, the experimental group exhibited significantly lower bone defect depth, bone height, bone height percentage, and bone gray level compared to the control group across different degrees of external root resorption (ERR) (P<0.05). There were statistically significant differences in bone defect depth, bone height, bone height percentage, and bone gray level between the two groups with different types of impaction(P<0.05), while no statistically significant difference was found in impaction depth and ERR severity comparison (P>0.05). None of the patients experienced complications such as infection or nerve injury postoperatively. CONCLUSIONS: The root dislocation method for ILTM extraction has certain guiding effects on the distal bone formation of M2M, and it has an effect on the improvement of periodontal health and postoperative reaction of M2M.

Key words: Mandibular complete bone embedded impacted teeth, Root dislocation first method, Mandibular second molar, Bone healing, Extraradicular absorption, Periodontal pocket