A case of a mandibular fracture with an unusual complication is reported. A 13-year-old boy was admitted four years after conservative treatment of a symphyseal fracture. He complained of recurrent swelling. A radiographic evaluation showed a horizontally laid permanent mandibular left lateral incisor (PMLLI) that had probably slid into the fracture line and provoked repetitive infection episodes. After a surgery, a clinical and radiological analysis showed satisfactory healing.