A 12-year-old girl was referred to the Endodontic Department of the Taipei Medical University Dental Clinic because of a resorptive lesion in her lower right second premolar. The lesion was identified on a periapical radiograph, which was taken by the referring dentist for observation of a sinus tract in the buccal area. The tooth had been treated at a local dental clinic 2 weeks prior to this examination.