Periapical lesions are found associated with the apex of a tooth without vitality, after contamination of the root canals, characterized radiographically by the presence of a radiolucent image at the apex of the affected element. The objective of this work is to report the regression of a periapical lesion, with a diagnosis of periapical abscess without fistula, after conventional endodontic treatment, confirmed through radiographic examinations and clinical images. A 24-year-old female patient complained of pain in the right anterior region and, days before the initial consultation, reported drainage of purulent secretion through the gums. In the intraoral physical examination, edema was observed at the bottom of the vestibule close to the incisors, pain on horizontal and vertical percussion and on the periapical radiograph the presence of a radiolucent image was observed close to the apex of tooth 36. A cold pulp sensitivity test was performed, obtaining a negative result. . With the purpose of decontaminating the root canals, endodontic treatment was carried out, using a preparation technique associated with the activation of chemical irrigants and intracanal medication between sessions. After a few weeks, the remission of clinical signs of inflammation and infection was observed and, after 3 months, radiographically, the beginning of repair of the lesion with bone formation was evident. The reported case highlights the importance of effective decontamination of the root canal as a determining factor for the regression process of periapical lesions. A longer period of clinical and radiographic follow-up of the case is necessary to verify complete repair.