Department of Child Dental Health, The London Hospital Medical College, Turner St, London El 2AD, United Kingdom.
J Xray Sci Technol. 1994 Jan 1;4(2):102-17. doi: 10.3233/XST-1994-4204.
In scanning microradiography (SMR), a thin section is stepped across a 15-μm diameter X-ray beam and the transmitted intensity measured at each point. This technique has permitted more accurate measurements of the spatial variation of the mineral concentration in sections of dentin and enamel than conventional photographic microradiography. Moreover, because the section is not in close contact with an emulsion, SMR allows continuous study while the specimen is bathed in a reaction solution. The present studies have been particularly directed to gaining an understanding of the formation and repair of carious lesions in teeth: one particular puzzle is subsurface demineralization, in which the initial loss of mineral appears to take place some 20 to 50 μm below the tooth surface. SMR studies are reported here on the demineralization in dilute acids and the subsequent partial remineralization in supersaturated calcium phosphate solutions in model systems for dental caries. In order to develop a theoretical model for de- and remineralization of carious lesions, it is necessary to quantify transport processes within the tooth. To this end, we are developing a method of measuring effective diffusion coefficients of strongly X-ray-absorbing ions in water within permeable solids in which the diffusion coefficient varies with position. The method uses sequential concentration/distance profiles determined by SMR. As a test, diffusion coefficients of potassium iodide in water within a permeable glass frit have been measured. X-ray microtomography (XMT) can be carried out by adding an axis of rotation to the SMR apparatus. Using this method, linear absorption coefficients, and hence mineral concentrations, can be measured in 15 X 15 X 15-μm3 voxels. This has advantages over SMR in that superposition within the depth of the section and errors in determining its thickness are avoided. XMT studies of de- and remineralization similar to those described above for SMR, and also XMT studies of the variation in mineral concentration in the cortical bone of a rat femur along its length, are reported.
在扫描显微放射摄影术（SMR）中，薄切片在 15μm 直径的 X 射线束上逐点移动，并测量每个点的透射强度。与传统的摄影显微放射摄影术相比，这种技术允许更准确地测量牙本质和牙釉质切片中矿物质浓度的空间变化。此外，由于切片与乳剂没有紧密接触，SMR 允许在反应溶液中浸泡标本的同时进行连续研究。目前的研究特别针对获得对牙齿龋病形成和修复的理解：一个特别的难题是表面下脱矿，其中初始矿物质损失似乎发生在牙齿表面以下 20 至 50μm 处。本研究报告了在稀酸中的脱矿作用以及随后在过饱和磷酸钙溶液中的部分再矿化作用，这些都是牙齿龋病的模型系统。为了为龋病病变的脱矿和再矿化建立理论模型，有必要量化牙齿内的传输过程。为此，我们正在开发一种在可渗透固体中测量水强烈吸收离子的有效扩散系数的方法，其中扩散系数随位置而变化。该方法使用 SMR 确定的顺序浓度/距离分布。作为测试，已经测量了在可渗透玻璃 frit 中的水中碘化钾的扩散系数。X 射线微断层摄影术（XMT）可以通过向 SMR 仪器添加旋转轴来进行。使用该方法，可以在 15×15×15μm3 体素中测量线性吸收系数，从而测量矿物质浓度。与 SMR 相比，这具有优势，因为避免了在切片深度内的叠加和确定其厚度的误差。报告了类似于 SMR 所述的脱矿和再矿化的 XMT 研究，以及大鼠股骨皮质骨沿其长度的矿物质浓度变化的 XMT 研究。
