Osteoradionecrosis (ORN) is a major complication of surgery or trauma in previously irradiated bone. This condition is often painful, debilitating and may result in significant bone loss. ORN of the mandible is the commonest site in patients who receive radiotherapy for head and neck cancer because of the relatively poor vascularization in this area. Risk factors include the total radiation dose, modality of treatment, fraction size and dose rate, oral hygiene, timing of tooth extractions as well as the continued use of tobacco and alcohol. Conversely, steroid use before or after radiation may have a protective effect related to the inhibition of the initial inflammatory phase of ORN. The management of this side effect is difficult and can result in bone or soft tissue loss, affecting the quality of life. The recommended treatment guidelines are irrigation, antibiotics, hyperbaric oxygen therapy and surgical techniques, including hemimandibulectomy and graft placements.

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The human genome contains approximately 3 billion base pairs (bp) of DNA coding for an estimated 50,000 to 100000 genes.

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