is the Notani classification.3 Patients who have ORN con- fined to the dentoalveolar bone are considered Class 1. When ORN involves the bone superior to the inferior alveolar canal (IAN), it is considered Class II. And when ORN progresses inferior to the IAN and there is a patho- logic fracture or an orocutaneous fistula, it is considered Class III. Serving as a guide for treatment, the various classification systems also provide a way for clinicians to discuss cases. PATHOPHYSIOLOGY Bones are resistant to ORN as long as there is healthy, intact soft tissue. Scarborough4 described three factors in the pathogenesis of ORN: exposure of radiotherapy above a critical dose, local injury, and the development of infec- tion. Studies in rhesus monkeys by Gowgiel5 showed vas- cular changes in the field of radiation that were seen as early as 1.5 weeks into radiation treatment. He suggested the difference in incidence of ORN in the maxilla and mandible was due to the vascular supply to these bones; the mandible, with its centrally located inferior alveolar vessels, compared to the maxilla, with its rich vascular plexus. In 1970, Meyer6 postulated a triad of radiation, proposed that, rather, it was the hypovascular, hypoxic and hypocellular environment that resulted in poor healing and the development of ORN. This was the accepted theory of the pathogenesis of ORN for decades, and led to hyperbaric oxygenation (HBO) as the treat- ment for prevention and management of ORN. key takeaways • Osteoradionecrosis (ORN) is defined as exposed necrotic bone for greater than three months in an area previously subjected to radiation therapy. • These patients typically present with exposed bone and inflamed, friable tissue — with or without purulent drainage. • Patients with ORN also have fibrosis of the muscles, leading to trismus — which makes oral hygiene and dental care difficult. • Computed tomogram scans and, in some cases, magnetic resonance imaging help clinicians evaluate the full extent of the jaw affected by ORN. • Though hyperbaric oxygenation (HBO) was long accepted as the standard of care in managing ORN, a Cochrane review concluded there is no evidence for or against the effectiveness of HBO in improving dental implant outcomes in radiated patients.12 • Caring for this patient population is challenging because there are no universally accepted guidelines for managing ORN today — and protocols for HBO that were once accepted as the standard of care are no longer recommended. 18 Decisions IN DENTISTRY • December 2017 FIGURE 3. Panorex radiograph of a patient who was treated with radiation in the head and neck region 10 years previously for management of tonsillar cancer. Note the sclerotic bone in the body of the mandible bilaterally. The mandible has a pathologic fracture, as seen by the disruption of the continuity of the inferior border of the mandible on the left side. Intraorally, both sites have exposed bone with purulent discharge. DecisionsInDentistry.com trauma and infection as the pathogenesis of ORN. Later, Marx7 FIGURE 2. Patient with an orocutaneous fistula secondary to progression of osteoradionecrosis to Stage III. Note the scar, which is evidence of a neck dissection for cancer treatment. Today, Marx’s theory on the genesis of ORN has been challenged by the fibroat- rophic theory,8 FIGURE 1. This is an intraoral image of a patient who has been treated with radiation therapy for an oral cavity cancer. Notice the exposed bone and inflamed tissue along the body of the mandible. cytes are damaged by free radicals from the radiation therapy, and this leads to inflammation and, thus, chronic activation of fibroblasts. Essentially, this chronic inflammatory state — the prefibrotic phase — leads to the organized fibrosis phase (areas of fibrosis in a poorly organized matrix). In the late fibroatrophic phase, this area is acellular and fibrotic — and with a dense matrix, the site’s ability to heal is compromised. HYPERBARIC OXYGENATION The use of HBO for patients with ORN undergoing dental extractions and implant placement has been accepted for decades. It was the protocol that patients receive 20 dives prior to surgery, followed by 10 dives after. Does this therapy pro- vide additional benefits for patients? Mul- tiple studies have been conducted to test the validity of hyperbaric oxygenation. In a multicenter study called the ORN 96 trial, patients were randomized into two arms: one arm received HBO and the other a placebo. Patients with ORN were subjected to 30 dives at 2.4 atmospheres for 90 minutes, followed by 10 dives. It was found that after one year, 19% of the subjects who received HBO experienced improved outcomes, whereas 32% of the placebo group showed improvement. The study was subsequently closed early due to these preliminary results.9 While there are numerous papers in the literature, there is only one randomized trial of HBO use in ORN treat- ment, and other articles are Level 2 (retrospective chart review and which suggests the osteo-
