Osteonecrosis of the jaw (ONJ) is a severe bone disease (osteonecrosis) that affects the jaws (the maxilla and the mandible). Various forms of ONJ have been described since 1861, and a number of causes have been suggested in the literature. Osteonecrosis of the jaw associated with bisphosphonate therapy, which is required by some cancer treatment regimens, has been identified and defined as a pathological entity (bisphosphonate-associated osteonecrosis of the jaw) since 2003. The possible risk from lower oral doses of bisphosphonates, taken by patients to prevent or treat osteoporosis, remains uncertain. Treatment options have been explored; however, severe cases of ONJ still require surgical removal of the affected bone. A thorough history and assessment of pre-existing systemic problems and possible sites of dental infection are required to help prevent the condition, especially if bisphosphonate therapy is considered. The definitive symptom of ONJ is the exposure of mandibular or maxillary bone through lesions in the gingiva that do not heal. Pain, inflammation of the surrounding soft tissue, secondary infection or drainage may or may not be present. The development of lesions is most frequent after invasive dental procedures, such as extractions, and is also known to occur spontaneously. There may be no symptoms for weeks or months, until lesions with exposed bone appear. Lesions are more common on the mandible than the maxilla. Pain and neuropathy Erythema and suppuration Bad breath Post radiation maxillary bone osteonecrosis is something that is found more in the lower jaw (mandible) rather than the maxilla (upper jaw) this is because there are many more blood vessels in the upper jaw. The symptoms of this are very similar to the symptoms of medication-related osteonecrosis of the jaw (MRONJ). Patients are in a lot of pain, the area may swell up, bone may be seen and fractures may take place. The patients may also have a dry mouth and find it difficult to keep their mouth clean.