Objectives: To assess clinical and radiologic findings from targeted radiotherapy to the rat maxilla and to compare findings with a recently developed rat model of mandibular osteoradionecrosis (ORN). Design: A prospective, controlled animal study. Subjects: Ten male Sprague-Dawley rats were divided into an experimental group receiving catheter-assisted high-dose-rate brachytherapy (n=6) and a control group with catheter-assisted sham therapy (n = 4). Interventions: The second left maxillary

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... ar was extracted 1 week after radiation, and the maxilla was harvested 3 weeks after dental extraction. Main Outcome Measure: We used a standardized method with micro-computed tomography to determine the ratio of bone volume to total volume of the dental extraction socket. Results: On the gross clinical examination, all rats had mucosal coverage of the dental extraction site, whereas only the brachytherapy group demonstrated scarring of the mucosa. The median bone volume to total volume was 0.21 for the brachytherapy group and 0.49 for the control group (P =.01). Conclusions: Similar to the mandible, the maxilla is susceptible to radiogenic bone injury as demonstrated by the significant decrease in bone volume of the radiated dental extraction socket. Despite radiologic similarities to mandibular ORN in the rat model, the maxilla demonstrated a more benign clinical course with a complete absence of bone exposure. Differences in the maxillary bone and microenvironment of the maxilla compared with the mandible may explain the subclinical response to radiation and lower incidence of maxillary ORN seen in patients. This maxillary model can be combined with our high-dose-rate mandibular ORN model to investigate these differences and better understand ORN.