External root resorption of second molars caused by impacted third molars: CBCT characteristics.

Objectives: This study aims to describe the cone-beam computed tomography (CBCT) characteristics of external root resorption (ERR) in second molars associated with impacted third molars.

Methods: This study analyzed 69 s molars diagnosed with ERR caused by impacted third molars in 52 patients (age range: 22-59 years; mean age = 31.2 ± 7.1 years) to identify key factors influencing the severity and occurrence of ERR. CBCT was used to assess the relationship between impacted third molar characteristics (position, angulation, proximity) and the extent of root resorption in adjacent second molars.

Results: ERR most commonly affected mandibular second molars (37 teeth: 60.0%, 47 teeth: 40.6%). Resorption extended to the pulp chamber in 47.9% of cases, while 40.6% was limited to superficial/middle dentin. 24.6% of the ERR sites were in communication with the oral cavity. 87% of impacted third molars were low-level, and 38% were completely bone-impacted. 26% had an angulation > 90° relative to the affected tooth. Complete bone impaction significantly correlated with ERR extending to the pulp chamber (65%, p < 0.05). ERR communicating with the oral cavity significantly increased pain on percussion. Younger patients were more likely to have ERR extending to the pulp chamber.

Conclusions: Low-level and complete bone impactions of impacted third molars significantly contribute to the development of ERR in adjacent second molars. Communication between the ERR site and the oral cavity is associated with a high risk of infection.