A 66-year-old man was referred to our hospital for further treatment of ORN of the mandible. He had undergone dental implant treatments on both sides of the mandible (#35, #36, #45, and #47) 7 years previously. All of the implants were osseointegrated and charged. The patient had been followed up regularly by his dentist, and the clinical course had remained uneventful. He experienced left oropharyngeal carcinoma and was treated with external radiotherapy of total dose 70 Gy 2 years after the implant treatment. Medical records revealed that his left mandible was included in the radiation field. He began to experience spontaneous pain and gingival swelling around the left mandibular implants 4 years after the oncologic radiotherapy. Under a clinical diagnosis of peri-implantitis, conservative treatment consisting of local irrigation and intermittent use of antibiotics had been carried out for 6 months. However, the symptoms became more serious and bone exposure around the dental implants appeared. He was then referred to our hospital for further treatment. Clinical examination revealed painful left cheek swelling with hypoesthesia of the left lower lip. The mouth opening range was restricted (1.5 fingerbreadth). Intraorally, exposed necrotic alveolar bone surrounding the left mandibular dental implants associated with mucosal inflammation and purulent discharge was observed (Fig. 1). On a panoramic X-ray image, poorly demarcated bone destruction around the left mandibular dental implants (fixtures at #35 and #36) was revealed, and the lesion reached the inferior border of the mandible and caused pathological fracture. No remarkable findings were observed around the right mandibular dental implant (Fig. 2). On CT examination, the mandibular bone was destroyed entirely in the left molar region and a fracture line across the mandible was evident (Fig. 3).

Initially, at our hospital, 30 sessions of hyperbaric oxygen therapy were carried out, but this resulted in only a slight improvement of symptoms. Thereafter, as the imaging studies proved no further progression of ORN, segmental mandibular resection and simultaneous reconstruction with a fibula free microvascular flap was performed. The affected tissue was determined and harvested based on the radiological changes in addition to the intraoperative macroscopic appearance of the bone. A vascularized fibula bone graft was fixed with a titanium reconstruction plate (Fig. 4). Histopathological assessment of the resected mandible showed loss of osteocytes and osteoblasts and filling of the bony cavities with fungus mass and inflammatory cell infiltration with fibrosis (Fig. 5). A final diagnosis of osteoradionecrosis of the mandible was confirmed. The postsurgical course was uneventful, and long-term follow-up has been successful. There have been signs of neither implantitis nor ORN around the right dental implants (Fig. 6).