Clinically, ORN presents as not healed, exposed bone in a previously irradiated area for at least 2 months unrelated to tumor recurrence . The common signs and symptoms are pain, foul odor, pus drainage, and fistula formation to the mucosa or skin. There have been many studies and classification of ORN. Marx  suggested staging system, but the system had a problem that it related to the response to HBO therapy. The staging system of Epstein et al.  is an amendment, but also had a problem that was focused on the presence of a pathologic fracture only. Schwartz and Kagan  developed a new clinical staging system for ORN of the mandible which is based on clinical experience for 25 years. Stage I is superficial involvement of the mandible and stage II is related to medullary bone necrosis. Stage III is diffuse involvement of the mandible. Division A and B of stage II and III is related to soft tissue ulceration including orocutaneous fistulation. According to the Schwartz and Kagan classification, our patients were all included in stage III division B.
In a series of 80 patients, Thorn et al.  found radiation therapy to the floor or mouth or oropharynx placed patients at the greatest risk for development of ORN. By contrast, Notani et al.  found in 87 patients with ORN that the most frequent primary tumor site was the tongue. Regardless of the sites, it is certain that the extent of the mandible included in the primary radiation field is a critical factor in determining the potential development of ORN. Tooth extraction in irradiated regions has been recognized as a major risk factor in the development of ORN [14–16]. Beumer et al.  noted that ORN associated with post-irradiation extraction required radical mandibular resection in 45 % of patients, as compared with 12 % in ORN associated with pre-irradiation extraction. Meanwhile, ORN can occur in patients who have never taken surgery. In our patients, no. 1 and 2 patients received radiotherapy for their NPC without operation. The other six patients received both surgery and postoperative radiotherapy.
The treatment of ORN is a combination of conservative management and surgical resection. Conservative managements are antibiotics injection, debridement, irrigation, and HBO therapy. HBO has been used widely to ORN patients since 1960s . According to Marx’s theory, HBO can be a good therapy because it can increase oxygen supply in the tissue, stimulating fibroblast proliferation, and angiogenesis . In early stage of ORN, HBO has been used with conservative management to avoid surgical resection of mandible [19, 20]. In a randomized trial by Marx et al. , HBO group had a 5.4 % incidence of ORN, as compared with 29.9 % in the penicillin group. However, Annane et al.  have reported a less than 5 % incidence of ORN following tooth extraction without HBO therapy. In our patients, four patients received HBO at an initial stage; however, there was no positive effect on ORN. In an advanced ORN (with fistula, pathologic fracture, involvement of inferior border of mandible), the patients require surgical resection with free vascularized bone graft. HBO therapy could not resolve these situations. All the necrotic bone must be removed by surgical resection, and bone margin must be a fresh bone. Gal et al.  showed that patients who underwent resection and free osteocutaneous flap reconstruction without HBO had fewer complications than those in whom HBO therapy had been used. In our practice, HBO therapy does not affect surgical result.
The treatment goals of ORN are the alleviation of symptoms and the recovery of aesthetic and function. Especially for patient with mandibular ORN, bone reconstruction is important because of mastication, swallowing, speech, and the harmony of the lower face. In order to achieve optimal surgical result, radical resection and immediate free flap reconstruction have been recommended in the surgical management of mandibular ORN [23, 24]. Placement of a non-viable graft in a radiated area is contraindicated as it is associated with significant complications . Many free-flap donor sites currently exist for mandible reconstruction, but FFF is the first choice option, because the fibula has ample bone length, consistent cross-sectional dimensions, no major variations of bone shape [24, 26]. Most patients required a large bony reconstruction (on average, 6.0 cm), and the complexity of the 3-dimensional bony defect can be restored by the number of osteotomies made to contour the flap adequately.
The surgical treatment of ORN patients is challenging. Several factors contribute to this difficulty. Patients who have received radiation therapy have impaired wound-healing capacity, and some have had previous neck dissection, resulting in the destruction of tissue planes. In a study of carotid-artery images in orthopantograms of 122 patients, Friedlander et al.  concluded that patients with total radiation doses sufficient to cause ORN are at a higher risk of developing carotid-artery atherosclerotic lesions than age-matched non-irradiated controls. Careful and delicate dissection and the use of contralateral side vessels for anastomosis can overcome some of these difficulties . Selection of the FFF is important when available vessels are present in the contralateral side. Interposition of vein graft is possible; however, it takes longer time than end-to-end anastomosis at the contralateral side. Our selection criteria are useful, and flaps were all successful when contralateral side anastomosis was performed. Our study involved eight patients with mandibulectomy and fibular reconstruction. Further studies with large number of patients or multicenter study are need.