Bone resorption effected by denture use and osteoporosis

骨矿物质含量（BMC）的调查有助于种植体治疗和骨质疏松症筛查的准确预后。BMC可以通过特殊设备测量，如定量计算机断层扫描。本研究对BMC测量系统进行了改进，采用全景x射线系统，一次获得牙弓及相关结构的全面覆盖。我们对该系统的测量性能进行了调查。本研究采用骨幻影作为参考和测试阶梯楔，X500CR（Morita Co.Ltd）作为全景x射线系统，Denoptix数字成像系统（Dentsply Co.Ltd.）作为图像输入设备。暴露条件为60kV， 10ma。将参考台阶楔固定在图像层的左侧，测试台阶楔的位置改变如下：1)层内或层外，2)前磨牙区或磨牙区。验证了该系统在各种条件下的测量精度和重现性。测定BMC的分辨率为0.01 ~ 0.04mg/cm^2 /像素，重现性为0.58 ~ 0.69%（CV）。层内与层外无显著差异（P < 0.05）。磨牙区测量值高于前磨牙区（P<0.05）。RMET值的变化是测量位置的函数（r=0.995 ~ 0.999）。调整后的RMET值精度为1.25%（相对误差）。本研究结果表明，在特定条件下，RMET值与BMC值的转换减小了被测BMC因设置位置变化而产生的变化，测量系统能够提供稳定的数据。该系统可用于种植体治疗和骨质疏松症筛查的准确预后。

The investigation of bone mineral content(BMC)is useful for an accurate prognosis for implant treatment and for osteoporosis screening. BMC can be measured by special devices, as quantitative computed tomography. In this study, BMC measuring system was improved by using panoramic X-ray system to obtain overall coverage of the dental arches and associated structures at a time. We surveyed the measuring performance of this system.We applied bone phantom to reference and test stepwedges, X500CR(Morita Co.Ltd.)to panoramic X-ray system and Denoptix digital imaging system(Dentsply Co.Ltd.)to image input device in this study. The exposure condition was 60kV, 10mAs. The reference stepwedge was fixed at left side on image layer, the position of test stepwedge was changed as followings 1)inside or outside of the layer, 2)premolar or molar region. We verified the measuring accuracy and reproducibility of this system at each condition.The resolution of BMC measuring was 0.01-0.04mg/cm^2 per pixel, the reproducibility was 0.58-0.69%(CV). The significant difference between inside and outside of the layer was not found(P>0.05). However, measured value in molar region was higher than that in premolar region(P<0.05). The change of RMET value was a function of the measurement position(r=0.995-0.999). The accuracy of adjusted RMET value was 1.25%(relative error).The results obtained in this study demonstrated that the conversion from RMET value to BMC value decreased the variation of measured BMC from change of setting position at a specific condition and that the measuring system was able to provide a stable data. This system may be useful for an accurate prognosis for implant treatment and for osteoporosis screening.