The relationship between bone strength and bone quality in rats fed with a low-magnesium (low-Mg) diet was examined. Twenty four-week-old male Wistar rats were divided into a control group (n = 10) and a low-Mg group (n = 10). Each group was fed with a conventional diet or a low-Mg diet (Mg, 6 mg/100 g diet) for 8 weeks, respectively. After the rats were sacrificed, bone strength, bone mineral content (BMC) and three-dimensional (3D) trabecular structure of the lumbar vertebra were measured, respectively. The results showed that the values of the BMC were almost the same between the control and the low-Mg diet groups. On the other hand, the bone strength of the low-Mg diet group was significantly lower than that of the control group (p < 0.01). 3D trabecular structure analysis showed a significant decrease (p < 0.05 or 0.01) in the trabecular structure of the low-Mg diet group as compared to the control group. These findings suggest that the bone strength in this model is not affected by the BMC but is strongly affected by the trabecular structure. The low-Mg diet model is considered to be an excellent model for examining bone quality.

[Purpose] The effects of experimental osteoporosis on the trabecular bone structure of the mandible in cynomolgus monkeys were examined by radiological bone morphometric analysis. [Methods] Ovariectomy (OVX) was performed on twelve 10-year-old female cynomolgus monkeys, which were fed a controlled diet for 2 years. Twelve monkeys in a sham control group were fed under the same conditions. Using a microfocus tube and computed radiography, the removed mandibular bone samples were imaged by standardized magnification radiography, and two-dimensional digital imaging data were obtained. The structural parameters, such as skeletal area, perimeter, number, complexity, continuity and anisotropy, were measured using radiological bone morphometric analysis. The bone mineral density (BMD) was measured by dual energy X-ray absorptiometry. The width of the cortical bone was measured using magnified radiographic images. [Results] There were no significant differences between the OVX and the sham control groups in the skeletal structure indicated by the skeletal volume, number, width, perimeter, complexity, continuity, separation and spacing. However, there were significant differences between the two groups in the BMD of the mandibular body, cortical bone width, anisotropy and some parameters of the skeletal continuity. Among these parameters, the difference in the thinning of the cortical bone was most significant. [Conclusions] Using two-dimensional digital radiographic image data, this study suggests that the cortical bone width is more useful than the trabecular bone structure as the morphologic parameter for diagnosis of osteoporosis in the mandibular body.

To investigate the effects of experimental osteoporosis on the trabecular structure of the mandibular condyle in cynomolgus monkeys by radiological bone morphometry, ovariectomy (OVX) was performed on 10-year-old female cynomolgus monkeys, which were fed a controlled diet for 2 years. Ten sham control groups were fed under the same conditions. Using a microfocus tube and computed radiography, the removed mandibular condyle samples were imaged by standardized magnification radiography. The structural parameters were measured using radiological bone morphometric analysis. The bone mineral density (BMD) was measured by dual energy X-ray absorptiometry. The thickness of the cortical bone was measured using magnified radiographic images. The thickness of the cortical bone and the BMD in the OVX group were significantly lower than in the sham group. In the results of skeletal structure of the mandibular condyle, the trabecular structure of the mandibular condyle was markedly deteriorated in the OVX group. The trabecular structure of the mandibular condyle for the OVX group was significantly decreased, thus it was suggested that osteoporosis is a potential risk factor of osteoarthritis of the temporomandibular joint.