Introduction Osteoradionecrosis (ORN) of the mandible is a debilitating complication of radiotherapy treatment for head and neck cancer. It may progress to orocutaneous fistula and pathological fracture. When conservative management fails, surgical resection with composite free flap reconstruction can improve symptoms and quality of life, though healing in irradiated fields remains challenging. This study assessed bony union and dental rehabilitation following reconstruction for ORN. Methods A retrospective cohort study was conducted of patients with ORN of the mandible or maxilla who underwent resection and composite free flap reconstruction between 2009 and 2024 at the Royal Brisbane and Women’s Hospital, with minimum one-year follow-up. Data collected included demographics, Brown defect classification, flap type, osteotomies, and radiation dose. Imaging (orthopantomogram and CT) was used to assess bony union at anterior and posterior junctions. Dental rehabilitation with osseointegrated implants was recorded. Results Ninety-four patients were included (mean age 69.1 years; 80% male). The mandible was affected in 90 cases. Mean radiation dose was 52.3 Gy. The most common defect was lateral mandibulectomy involving the ipsilateral canine region. Fibula free flaps were most common (62.8%), followed by scapula flaps (26.6%). Bony union occurred in 98.9% of anterior sites and 92.3% of posterior sites, with no intraflap non-unions. The difference between anterior and posterior union rates was significant (p=0.03). Dental implants were placed in 28.7% of patients. Conclusion Composite free flap reconstruction achieves high rates of bony union in ORN despite prior radiation. Lower posterior union rates suggest the importance of resection at lower-dose margins, which may require condylectomy to optimise outcomes.