[Endodontic retreatment of a maxillary second molar with chronic apical periodontitis and separated instrument: A case report].

This case report describes the micro-endodontic retreatment and comprehensive management of a complex left maxillary second molar presenting with multiple complications. The patient, a 41-year-old female, presented with recurrent gingival swelling associated with the tooth for more than six months. The tooth had a history of root canal treatment, fiber post placement, and full crown restoration two years earlier. Cone-beam CT (CBCT) revealed a separated metallic instrument approximately 5 mm in length in the apical region of the mesiobuccal root, a fiber post in the palatal root, underfilled root canal obturation, and periapical radiolucency involving the mesiobuccal, distobuccal and palatal roots. A diagnosis of chronic periapical periodontitis (post-endodontic treatment) was established. The primary challenges included the limited access to the left maxillary second molar, the deeply embedded apical instrument segment, and the high risk for complications, such as root fracture or secondary perforation during retrieval attempts. The treatment strategy involved removal of the separated instrument and retreatment under a dental operating microscope. With ultrasonic assistance, the palatal fiber post and the coronal segment (2.5 mm) of the separated instrument from the mesiobuccal canal were successfully removed. An iatrogenic lateral perforation occurred in the mesiobuccal canal near the furcation area during the instrument retrieval procedure. Given the depth and high risk of further damage from retrieving the remaining apical segment (2 mm), a conservative and flexible approach was adopted using the bypass technique. After successful bypassing, thorough chemo-mechanical debridement was performed, followed by obturation using the warm vertical compaction technique. The iatrogenic perforation on the distal wall of the mesiobuccal canal was immediately repaired with a bioceramic material (iRoot BP) for its superior sealing and bioactivity. The tooth was then restored with a full crown. A 10-month follow-up showed that the patient was asymptomatic with complete fistula healing and radiographic examination revealed favorable healing of the periapical lesion. This case demonstrates that, in complex root canal retreatment cases involving retained instruments and iatrogenic perforations, the integration of advanced diagnostic tools (