External root resorption of second molars caused by impacted third molars: an observational study in panoramic radiographs

Abstract Objective This research investigate the presence of external root resorption (ERR) in second molars caused by impacted third molars in panoramic radiographs, relating to the position of third molars according to classification of Winter, Pell and Gregory. Material and method A cross-sectional, retrospective study using panoramic radiographs obtained from January 2014 to December 2015. The inclusion criterion was the presence of a second molar adjacent to an impacted third molar. Data were analyzed using descriptive and inferential statistics. Pearson's Chi-Square Test and Fisher's Exact Test (p≤0.05) were performed. Result The sample consisted of 584 panoramic radiographs, 356 (60.95%) of women, and 228 (39.05%) of men, the mean age was 25.31 years. The prevalence of ERR was 12.5%, and the group of 14-24 year olds was the most affected (p = 0.46). The presence of ERR was statistically higher in the mandible (42.1%) with p=0.01. The ERR located in the cervical (57.1%) and medium (58.8%) thirds was proportionally higher in the teeth with B2 (p=0.02) and mesio-angular positions (p=0.26). Conclusion The prevalence of ERR in second molars, caused by impacted third molars, was shown to be similar to results found in the literature, with no gender preference, this affects young patients, occurring frequently in mandible teeth, and presents greater severity in the cervical and middle thirds. The B2 and mesio-angular positions were more prone to ERR.摘要 目的：本研究旨在通过全景X线片（panoramic radiographs），探究阻生第三磨牙（impacted third molars）导致的第二磨牙外牙根吸收（external root resorption, ERR）发生情况，并结合Winter、Pell和Gregory分类标准分析第三磨牙位置与该病变的关联。 材料与方法：本研究为回顾性横断面研究，使用2014年1月至2015年12月期间获取的全景X线片。纳入标准为存在与阻生第三磨牙相邻的第二磨牙。采用描述性统计与推断性统计对数据进行分析，执行Pearson卡方检验与Fisher确切概率法（检验水准p≤0.05）。 结果：本研究样本共纳入584张全景X线片，其中女性356例（60.95%），男性228例（39.05%），平均年龄25.31岁。外牙根吸收的患病率为12.5%，14~24岁年龄段的受累病例最多，但组间差异无统计学意义（p=0.46）。下颌骨区域的外牙根吸收发生率显著更高（42.1%，p=0.01）。当阻生第三磨牙为B2位时，病变累及牙颈三分之一（57.1%）与牙中三分之一（58.8%）的比例更高（p=0.02）；近中阻生位的相关比例也相对更高（p=0.26）。 结论：阻生第三磨牙所致第二磨牙外牙根吸收的患病率与现有文献报道结果相近，无性别偏好；该病变好发于青年患者，常见于下颌牙齿，且多累及牙颈与牙中三分之一，病变程度更为严重。B2位与近中阻生位的第三磨牙更易引发外牙根吸收。