Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 18 0 2021 12 08 3997 3997 Behnam Bolhari Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran Faranak Noori Department of Endodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Hadi Assadian Department of Endodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran 2021 03 15 2021 08 10 Dens invagination (DI) is a dental anomaly that can cause pulpal and periapical pathoses of the affected tooth. We describe the treatment of a healthy 18-year-old female with a chief complaint of recurrent facial swelling pertaining to a peg-shaped maxillary lateral incisor with DI. Examinations showed necrosis of the involved tooth with symptomatic apical periodontitis. Cone-beam computed tomography corresponded to Oehlers type II DI. Orthograde endodontic treatment was performed. To completely debride the canal and resolve the persistent purulent discharge, various methods and medicaments were used in separate sessions including passive ultrasonic activation of 5.25% sodium hypochlorite solution, calcium hydroxide mixed with 2% chlorhexidine, and double antibiotic paste as intracanal medicament. After resolution of the symptoms, the root canal and the invaginated space were filled by a mineral trioxide aggregate plug and backfilled with thermoplasticized gutta-percha. At the one-year follow-up, complete bone healing was noted in the affected periradicular area. https://fid.tums.ac.ir/index.php/fid/article/view/3997