Materials and methods: Patients come for dental health examination or diseases related to the maxillofacial region at the Department of Odonto-Stomatology, Hanoi Medical University Hospital and the Center for High-Tech Dental Examination and Treatment, Institute of Odonto-Stomatology, Hanoi Medical University, was assigned to take CT Conbeam film, on the film appeared the image of extrinsic resorption of the roots of the mandibular second molars because the lower wisdom teeth were included in the study sample. Research method: Cross-sectional, prospective, convenient sample selection, patients with CT Conbeam films satisfying the selection criteria were included in the study sample.