An Animal Model to Study Bisphosphonates Associated Osteonecrosis of the Jaw

The pathogenesis of osteonecrosis of the jaws (ONJ) in patients treated with intravenous bisphosphonates is still not completely understood, and likely involves both reduction in blood supply and the activity of oral bacteria. We present an animal model of ONJ, which will significant contribute to the understanding of the aetiopathogenesis of this condition. Five skeletally-mature female Wistar rats (weight 450 g) were given intravenous zoledronic acid 0.04 mg in saline solution (0.2 mg/ml) once a week for 5 weeks. After 2 weeks, the animals underwent the extraction of the upper right first molar, followed by the creation of a 4 mm-diameter bone defect on the same site under general anaesthesia. After 7 weeks from the extraction, the animals were clinically examined and a static bone-scintigraphy using 99mTc-MDP methylene diphosphonate was performed with a gamma camera equipped with pinhole collimator (Siemens-Ecam). After an additional week, the rats were sacrificed and a Computed Tomography (CT) was carried out. Samples obtained from the bone defect were decalcified and prepared for histological assessment. Five rats, not treated with zoledronic acid and exposed to the same surgical treatment, were used as controls. Histological and imaging features were assessed blindly. At 7 weeks after the extraction, all the rats treated with zoledronic acid showed impair healing, expansion of the defect and bone exposure. These features were confirmed by the scintigraphy, which showed abnormal localized activity in comparison with the surrounding tissues. On clinical examination, the rats of the control group demonstrated epithelialization of the bone defect and a normal uptake of the contrast medium during the scan. The CT scan disclosed irregularity of the cortical margin and destruction of the cortical bone, which were not evident in the control group. The histology showed sheets of necrotic bone, with loss of osteocytes from their lacunae and peripheral resorption. No inflammatory infiltrate was observed. The control group instead demonstrated normal bone healing. All animals were treated according with the guiding principles for experimental procedures found in the Declaration of Helsinki of the World Medical Association. Based on this study, the rat treated with zoledronic acid can be considered a novel, reliable and reproducible model to better understand the pathophysiology of ONJ and to develop a therapeutic approach.