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Objective: Osteonecrosis of the jaw (ONJ) in association with use of bisphosphonate (BP) has been described primarily in cancer patients receiving high-dose intravenous BP. The frequency of the condition in patients with osteoporosis appears to be low. We evaluated the frequency of BP-associated ONJ in Ontario in the cancer population and in those receiving BP for osteoporosis and metabolic bone disease., Methods: A survey developed by representatives of the Ontario Society of Oral and Maxillofacial Surgeons was mailed to Ontario oral and maxillofacial surgeons (OMFS) in December 2006, asking oral surgeons to provide information on cases of ONJ seen in the previous 3 calendar years (2004 to 2006). OMFS were subsequently contacted by telephone if they had not responded or if they had reported cases of ONJ. The frequency of ONJ in association with BP use was estimated from the number of patients with filled prescriptions for BP in Ontario between 2004 and 2006. The cumulative incidence of ONJ was calculated separately for patients using intravenous (IV) BP for cancer treatment and for patients using oral or IV BP for osteoporosis or other metabolic bone disease., Results: Between 2004 and 2006, 32 ONJ cases were identified. Nineteen patients received IV BP for cancer treatment and 13 patients received oral or IV BP for osteoporosis or metabolic bone disease. Over a 3-year period the cumulative incidence of BP-associated ONJ was 0.442% of cancer patient observations (442 per 100,000) and 0.001% of osteoporosis or other metabolic bone disease observations (1.04 per 100,000). The relative risk of low dose IV/oral BP-associated ONJ was 0.002 (95% CI 0.001, 0.005) compared to high-dose IV BP. Other risk factors for ONJ were present in all cases in whom detailed assessment was available. The median duration of exposure to BP was 42 months (range 36 to 120 mo) and 42 months (range 11 to 79 mo) in osteoporosis patients and cancer patients, respectively., Conclusion: Over a 3-year period, the cumulative incidence for BP-associated ONJ was 0.442% of cancer patient observations (442 per 100,000) and 0.001% of osteoporosis or metabolic bone disease observations (1.04 per 100,000). This study provides an approximate frequency of BP-associated ONJ in Canada. These data need to be quantified prospectively with accurate assessment of coexisting risk factors.