[Purpose] To develop a digital radiographic bone trabecular structure analyzing system and to applied it to mandible. [Methods] Structural change was simulated by removing spongy bone in human dried mandible. Using a morphological filter processing, the skeletal features were extracted from digital radiographic image data obtained by computed radiography before and after the removal of spongy bone. The skeletal volume, surface, thickness, number, separation, complexity, spacing continuity and connectivity on the skeletal binary images were determined by morphometric indices calculation, star volume analysis and node-strut analysis. Using these quantified skeletal feature parameters, a mapping sheet for the structural evaluation was produced. The correlation between the fluctuation rate of each parameter after the removal of spongy bone with respect to the value before the removal of spongy bone and simulated structural change was examined. [Results] The skeletal binary image data quantified sixteen skeletal feature parameters using morphometric indices calculation, star volume analysis and node-strut analysis. These parameters agreed with the theoretical fluctuation pattern in the simulated skeletal structure deterioration of the mandibular bone trabeculae. [Conclusion] Using a morphological filter and bone histomorphometry, the radiological bone-morphometric analyzing system is useful for the evaluation of the mandibular trabecular structure.

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.

To develop an osseointegration analyzing system for dental implants, a new analyzing system which can assess the level of osseointegration between an implant and trabecular bone was constructed using digital radiography with morphological filter and node-strut analysis. For assessment of this system, a grayscale test chart that simulates six levels of an osseointegration was created. In addition, digital implant images were made in which the trabecular pattern around the implant was varied over a total of five levels. Implant osseointegration was evaluated on the basis of seven parameters related to the number of nodes (Nd) and terminuses (Tm) of the skeleton bound to the implant (Im) and the skeletal length. The seven parameters were as follows: the number of struts connecting the Im with the Nd and Tm (N.ImNd, N.ImTm), the total number of N.ImNd and N.ImTm (N.Im), the strut length connecting the Im with the Nd and Tm (ImNd, ImTm), and the ratios of the struts connecting the Im with the Nd and Tm (ImNd/TSL, ImTm/TSL), where TSL is the total strut length.Strong correlations (R² = 0.971-1.0) between the theoretical values from the test charts and the measured values were demonstrated. N.ImNd showed the strongest correlation, R² = 0.948, from the digital implant images, followed by N.Im and ImNd, with correlations of R² = 0.86 and R² = 0.84, respectively. This new system for evaluating implant osseointegration by applying morphological processing and node-strut analysis could be useful for computer-assisted diagnosis of digital dental implant images.