Osteonecrosis is a condition of bone necrosis caused by infection, radiation, drugs or other causes. Osteomyelitis is an infection of odontogenic origin. Necrosis occurs due to reduced blood supply to the bone, which is a consequence of obstruction of blood vessels because of the increased intramedullary pressure. Osteoradionecrosis occurs due to damaged bone cells and decreased blood supply caused by radiation in the head and neck area. Hypocellularity and hypoxia hinder bone healing after an injury. Drug-induced osteonecrosis occurs due to the effect of antiresorptive drugs on osteoclasts or due to the effect of antiangiogenic drugs on the formation of new blood vessels, which makes healing after extraction difficult. Such conditions are best prevented by remediation prior to radiation or drug therapy. Infections are treated with antibiotics, while progressive conditions should be treated surgically. Surgery removes a devitalized bone, thereby promoting healing. Clinically, osteonecrosis manifests as an exposed necrotic bone that does not heal. The conditions differ according to etiology, while clinically there are no major differences. Information about the cause of the disease is obtained from a detailed medical history