Experimental Radio-Osteonecrosis of the Jaws

¹ Department of Anatomy and Zoller Memorial Dental Clinic, University of Chicago

The maxilla and mandible of eighteen M. rhesus monkeys were subjected to external fractionated irradiation ranging from 4,500 to 11,000 r.

The time of onset of necrosis and the dosage of irradiation were in direct relationship to each other. The severity and extent of the necrosis were in direct relationship to the time of onset.

The gross necrotic lesion always began in the interdental papilla of the mandibular molar that was in the center of the field of irradiation. From this point the necrosis extended to involve the cervical gingiva, the attached gingiva, and the buccal mucosa. In the maxilla the necrosis was confined to the interdental papilla and cervical gingiva. The palate was involved only in case of extensive necrosis.

Microscopically, the interdental papilla was the first area that demonstrated inflammation. This condition was followed by ulceration of the epithelial attachment and necrosis of the underlying corium. The necrosis spread by two routes: via the periodontal ligament and via the gingival tissue. The most common route of extension was via the periodontal ligament, with the contiguous structures involved by direct extension.

Radio-osteonecrosis appears to result primarily from the direct effect of irradiation on the osteocyte. Changes in the blood vessels played a role in the aggravation and prolongation of the irradiation effects. Radiation produced marked thickening of the walls of arteries and arterioles. The veins and capillaries were not affected. There was no evidence of ischemic necrosis.

Radio-osteonecrosis can occur under an intact gingiva. A dormant or latent radio- osteonecrosis requires disruption of the gingival surface to become grossly evident.

With a sufficiently long period of time, a restoration of the radio-osteonecrotic damage is possible.

The difference between the irradiation effects on the mandible and maxilla is discussed.