Abstract: Objective　To study the relationship between the impacted third molar and external root resorption （ERR） of the second molar，and to provide basis for the prevention and treatment of such cases. Methods　The data of 85 patients with 105 impacted third molars and the ERR of second molars who were treated at our institution from 2013 to 2017 were retrospectively analyzed. The ERR in second molars was identified on CBCT multiplanar images. The asociations between detection rate as well as dgree of ERR and multiple clinical parameters were statistically analyzed by Chi-square test or Fisher′s exact probabilities. Results　The detection rate of ERR in second molars was 44.8%，and there was no significant difference between sex （P > 0.05）. The difference in the detection rate of ERR was statistically significant between group younger than 20 years old and the other three groups （＞20～30，＞30～40，and ＞40 years） （P < 0.05），while there was no significant difference among the latter three groups （P > 0.05）. The detection rate of ERR in the second molars increased with the increase of the angle of occlusion and the depth of position of the third molars. The difference in degree of ERR between the upper and the lower jaw was statistically significant （P < 0.05）. There was no significant difference in the degree of ERR between sex，age and impaction type （P > 0.05）. Conclusion　There is no gender difference in the detection rate of ERR in second molars，which is related to the age of patients and the position，angle and depth of impacted third molars. The ERR that occurs in the mandible is more serious than in the upper jaw. The impacted third molars that cause ERR should be actively extracted，especially those in the lower jaw.

Key words: external root resorption, ERR；cone beam CT, CBCT；impaction of the third molar；second molar；impacted tooth classification

摘要： 目的　研究第三磨牙阻生与相邻第二磨牙牙根外吸收（external root resorption，ERR）的关系，并为此类病例的防治处理提供依据。方法　回顾性分析南方医科大学深圳口腔医院2013—2017年收治的85例第三磨牙阻生患者的105颗阻生牙及相邻第二磨牙ERR情况。利用CBCT对第二磨牙ERR进行检测。采用χ2检验或Fisher确切概率法分析第二磨牙ERR检出率及其严重程度与临床特征的关系。结果　第二磨牙ERR的检出率为44.8%，男、女差异无统计学意义（P＞0.05）；各年龄组比较发现，≤20岁组与＞20～30岁、＞30～40岁和＞40岁三组之间的差异有统计学意义（P＜0.05），而后三组间差异无统计学意义（P＞0.05）。第二磨牙ERR的检出率随第三磨牙阻生角度的变大和位置的变深逐渐增加。第二磨牙ERR的严重程度在上、下颌之间的差异有统计学意义（P＜0.05）；在性别、年龄、阻生第三磨牙类型的差异无统计学意义（P＞0.05）。结论　第二磨牙ERR检出率无性别差异，与年龄及阻生第三磨牙位置、角度、深度相关。发生于下颌的第二磨牙ERR要比上颌的严重。对于造成第二磨牙ERR的阻生第三磨牙要积极拔除，特别是发生于下颌者。

关键词: 牙根外吸收, 锥形束CT, 第三磨牙阻生, 第二磨牙, 阻生牙分类