OBJECTIVE: Oral health status is a risk factor for postradiation bone complications (also known as osteoradionecrosis [ORN]), and oral health care is an important element in the prevention of this condition. Some authors recommend extracting teeth with a questionable prognosis and either gross mobility or periodontal disease. However, the criteria for making such decisions remain to be elucidated. In addition, the specific details of the association between oral health status and ORN have not yet been clearly demonstrated. The purpose of this study was to clarify the relationship between oral health status and the development of ORN. STUDY DESIGN: Thirty-nine head and neck cancer patients whose radiation fields included both the teeth and the mandible were followed for > or = 3 years after radiotherapy. Among these patients, 6 suffered from ORN (ORN group), and the other 33 did not experience the condition (non-ORN group). We analyzed the patient factors, radiation factors, and oral health factors related to the complication. RESULTS: The onset of ORN occurred from 18 months to 51 months after radiotherapy. The radiation dose in the oral cavity and the oral health status before radiotherapy were not significant risk factors for ORN. However, the oral health status at 1 year or 2 years after radiotherapy was significantly associated with the development of ORN. The oral health conditions that increased the risk of ORN were > 5 mm periodontal pocket depth, > 40% dental plaque score, > 60% alveolar bone loss level, and a grade 3 radiographic periodontal status. CONCLUSION: This is the first report to show the changes in the oral health status before and after radiotherapy regarding the development of ORN. The results support the periodontal status that almost all clinicians agree on as indications for preradiation teeth extraction (namely, periodontal pockets of > 5 mm) to prevent ORN. Good oral health status, especially after radiotherapy, is very important in the prevention of ORN, and we recommend periodical dental management and care by well trained dentists and dental hygienists to avoid the condition.