Orthodontic treatment of a mandibular incisor fenestration resulting from a broken retainer

•A 36-year-old man experienced orthodontic relapse with incisor fenestration.•A mandibular bonded retainer had partially debonded and broken 4 years earlier.•The left lateral incisor received the entire load and was avulsed.•Treatment included root repositioning, endodontics, apicoectomy, leveling, and aligning.•Treatment outcomes were excellent, and the tooth remained stable 1 year later.

This article describes the orthodontic relapse with mandibular incisor fenestration in a 36-year-old man who had undergone orthodontic treatment 21 years previously. The patient reported that his mandibular 3 × 3 bonded retainer had been partially debonded and broken 4 years earlier. The mandibular left lateral incisor remained bonded to the retainer and received the entire load of the incisors; consequently, there was extreme labial movement of the root, resulting in dental avulsion. As part of the treatment, the root was repositioned lingually using a titanium-molybdenum segmented archwire for 8 months, followed by endodontic treatment, an apicoectomy, and 4 months of alignment and leveling of both arches. The treatment outcomes were excellent, and the tooth remained stable, with good integrity of the mesial, distal, and lingual alveolar bones and periodontal ligament. The 1-year follow-up showed good stability of the results.