Prevalence of second molar external root resorption caused by mandibular third molars: a CBCT study

The aims of this study were to use cone beam computed tomographic (CBCT) scans to assess the prevalence of second molar external root resorption (ERR) caused by impacted mandibular third molars and to associate the location and severity of ERR with the third molar position using 2 classification systems-1 proposed by Pell and Gregory and the other proposed by Winter. In this cross-sectional study, 2 calibrated observers evaluated a total of 107 CBCT scans (71 female and 36 male patients). After the presence or absence of ERR was determined, ERR was classified according to its location (cervical, middle, apical third, or root apex) and severity (mild, moderate, or severe resorption). The data were assessed with the Pearson chi-square test, the chi-square test for linear trend, and Poisson regression analysis. The significance level was set at P < 0.05. The prevalence of second molar ERR in the sample as a whole was 47.7% (n = 51). The prevalence was significantly higher (69.4%) for male patients (P = 0.002; Pearson chi-square test). The probability that ERR would affect the second molar was 1.71 times greater when the third molar exhibited the Pell and Gregory class IC position (95% CI, 1.27-2.31) and 1.64 times greater when the third molar exhibited the Winter mesioangular position (95% CI, 1.38-1.95). There was a statistically significant association between ERR location and severity; the cervical third was the most affected by mild ERR and the middle third was the most affected by severe ERR. The prevalence of mandibular second molar ERR caused by impacted third molars is high, especially in male patients. Mandibular third molars in the Pell and Gregory class IC position or Winter mesioangular position demonstrated greater potential to result in ERR of the adjacent second molar.