 Post radiation maxillary bone osteonecrosis is something that is found more in the lower jaw (mandible) rather than the maxilla (upper jaw) this is because there are many more blood vessels in the lower jaw.The symptoms of this are very similar to the symptoms of medication-related osteonecrosis of the jaw (MRONJ).Patients are in a lot of pain, the area may swell up, bone may be seen and fractures may take place.