INTRODUCTION: The aim of this presentation is to demonstrate retreatment and apexification treatment with MTA in a patient who has previously undergone unsuccessful apical resection. CASE REPORT: A 38-year-old systemically healthy female patient presented to our clinic with a complaint of pain in tooth #21. The patient’s history revealed that she had undergone root canal treatment and apical resection procedure 10 years ago. Clinical and radiographic examination revealed a periapical radiolucent lesion associated with tooth #21, and a positive response obtained palpation sensitivity. The presence of a sinus tract at the apical level of the tooth was detected. Retreatment procedure was initiated, and the previous root canal filling was removed with irrigation using 2.5% sodium hypochlorite and 17% EDTA. In the first appointment, calcium hydroxide was placed in the canal, and it was renewed after one week. In the final appointment, the patient, whose symptoms had resolved, underwent apical MTA plug placement and thermoplastic gutta-percha root canal filling. A 6-month follow-up was performed, and the patient is currently under continued observation. CONCLUSION: It can be observed that retreatment, MTA plug application, and thermoplastic gutta-percha filling can be successful in preserving a tooth with an open apex and disrupted apical constriction resulting from apical resection without retrograde filling.