[Osteoradionecrosis. I. Etiology, pathogenesis, clinical aspects and risk factors].

In curative therapy of mouth-cavity and oropharyngeal carcinomas the osteoradionecrosis has to be accepted as a calculated risk with an incidence of 4-35%. It is the question of a radio-caused bone death that comes about by progressive and irreversible morphological alterations at bones and at vessels: Loss of osteocytes, active osteoblasts and osteoclasts (hypocellularity), injury of normal bone metabolism, slackening of regeneration process, extreme susceptibility to infections of the devitalized bone, radio-induced obliterating endarteritis with hyalinization, thrombosis and fibrosing of vessels, obliteration of the lumen and gradual reduction of blood-supply at the level of tissue (hypovascularity and hypoxemia: Aseptic osteoradionecrosis, radio-osteonecrosis). If there is a secondary infection of dental, periodontal or traumatic origin additionally, the condition explodes as septic osteoradionecrosis with the symptoms and findings of radio-osteomyelitis. The osteoradionecrosis begins more frequently in the mandibula than in the maxilla. The cumulative incidence is 30% after 6, 60% after 12, and more than 80% after 24 months. The duration of osteoradionecrosis follows an exponential curve with constant probability of necrosis termination at any moment after necrosis event in which the monthly probability of necrosis healing is nearly 0.06. Risk factors for formation of an osteoradionecrosis are tumor neighbourhood to bones and teeth, tumor and mandibula dosis, tumor stage, irradiation technique, status of teeth as well as moment and carrying out of tooth extractions. Tumors in neighbourhood of mandibula have a fivefold higher risk, with 80 Gy irradiated patients a 2.9-fold and toothed patients a 2.6-fold, altogether high-risk patients have a 17.7-fold higher necrosis risk than low-risk patients. Promoting factors are caries, parodontosis, a periapical pathology, a trauma, irritation by artificial teeth, elective tooth extraction before irradiation, tooth extraction after irradiation as well as jaw operations because of remains or recurrence of the tumor.