关键词: 下颌第三磨牙, 锥形束CT, 邻接关系, 食物嵌塞

Abstract: Objective    To investigate the long-term effects of mandibular third molar extraction on the proximal contact relationship between the adjacent first and second molars and to analyze the related influencing factors. Methods A retrospective analysis was conducted on the clinical and imaging data of 145 patients who underwent cone beam CT（CBCT）examination at School of Stomatology，the Fourth Military Medical University from 2018 to 2024. According to the time of the last CBCT examination，all patients were divided into four groups：6 - 12 months after extraction（n = 15），> 12 - 24 months（n = 40），> 24 - 36 months（n = 40），and > 36 months（n = 50）. Three‑dimension measurement software was used to quantitatively evaluate the differences in contact line length，buccal embrasure angle，lingual embrasure angle，occlusal embrasure angle，and second molar axial inclination before and after mandibular third molar extraction. The influence of gender，age，impaction type，and follow-up time on the amount of change（difference between postoperative and preoperative measurements）was analyzed. Results    After mandibular third molar extraction，the overall contact line length ［preoperative vs. postoperative：（2.42 ± 0.52）mm vs.（2.23 ± 0.61）mm］and lingual embrasure angle［preoperative vs. postoperative：（47.79 ± 9.88）° vs.（45.84 ± 9.71）°］between the adjacent first and second molars decreased significantly in all patients. The contact line length in the > 12 - 24 months group and the > 36 months group［（2.15 ± 0.54）mm and（2.24 ± 0.72）mm，respectively］was significantly smaller than the preoperative value［（2.36 ± 0.55）mm and（2.48 ± 0.61）mm，respectively］（all P < 0.05）. No significant differences were found in the other indicators either in the overall analysis or among groups（all P > 0.05）. Regarding gender，the occlusal embrasure angle and M2 axial inclination of the first and second molars increased postoperatively in male patients［amount of change：（1.29 ± 9.59）° and（0.47 ± 4.09）°，respectively］but decreased in female patients［amount of change：（-2.01 ± 10.17）° and（-2.05 ± 6.71）°，respectively］，with significant differences（t = -1.993 and -2.639，P = 0.048 and 0.009，respectively）. No significant differences were found in the amount of change in the other indicators between genders（all P > 0.05）. Regarding Winter classification，the lingual embrasure angle increased postoperatively in patients with mesioangular impaction［amount of change：（0.57 ± 10.13）°］but decreased in patients with vertical and horizontal impactions［amount of change：（-1.24 ± 10.85）° and（-5.28 ± 11.38）°，respectively］，and the difference among the three was statistically significant（F = 3.452，P = 0.034）. Further pairwise comparison showed that the amount of change in lingual embrasure angle in patients with mesioangular impaction was significantly greater than that in patients with horizontal impaction（t = 2.540，P = 0.012）. No significant differences were found in the amount of change in the other indicators among different Winter classifications（all P > 0.05）. There were no significant differences in the amount of change in any indicator among groups of different age，Pell-Gregory classification，or follow-up time（all P > 0.05）. Conclusion    Mandibular third molar extraction can alter the proximal contact relationship between the adjacent first and second molars，and these changes are influenced by gender and Winter impaction type. When making decisions about mandibular third molar extraction，clinicians should fully consider the above factors，strengthen long-term postoperative follow-up for high-risk patients，focus on evaluating the proximal contact relationship and the morphology of the food escape way，and provide timely oral maintenance guidance to reduce the risk of postoperative periodontal and dental diseases.

Key words: mandibular third molar, cone beam CT, proximal contact relationship, food impaction