Impacted third molars (M3s) may lead to external root resorption (ERR) and dental caries (DC) in the adjacent second molars (M2s). The aim of this study was to identify the risk factors for ERR and DC in M2s associated with impacted M3s.
We implemented a cross-sectional study and enrolled a sample composed of patients with M3s and M2s present and cone-beam computed tomography (CBCT) scans available for review. If there was contact between the M2 and the adjacent M3 and the border of radiolucency was more distinct, the case was considered ERR. Apart from that, the case was considered DC. Potential predictor variables were defined as age, gender, tooth number, M2-M3 contact, root development in M3, M3 inclination, M3 impaction type, and M3 follicular diameter. Outcomes of the study were DC and ERR in M2s. CBCT was used to detect the presence of DC and ERR in M2s.
A total of 250 eligible images of M3s in the upper and lower jaws of 167 patients were included. The mean age of the patients with CBCT images available was 26.08 ± 4 years (range, 18 to 40), and 43.6% of the patients were men. Factors associated with a significantly increased frequency of ERR in M2s included maxillary location, presence of M2-M3 contact, and mesioangular inclination (P < .005). DC in M2s was significantly more likely to occur in those with absence of contact between M2 and M3 (P < .005).
The results of this study showed an increased risk of ERR to be associated with maxillary molars, mesioangular inclination, and presence of M2-M3 contact. The variable associated with an increased risk of DC was the absence of M2-M3 contact.

Copyright © 2020. Published by Elsevier Inc.