Shimoda S, Aoba T, Moreno E C, Miake Y
Forsyth Dental Center, Boston, Massachusetts 02115.
J Dent Res. 1990 Nov;69(11):1731-40. doi: 10.1177/00220345900690110501.
The composition of enamel mineral corresponds to that of a calcium carbonato-apatite. For insight to be gained into the precipitation of carbonato-apatites having specific properties (crystal size, morphology, and carbonate incorporation into the crystal lattice), apatites were prepared at 80 degrees C in aqueous systems having various CO3 concentrations and pH values of around 7.5 or 10.5 (+/- 0.5). The various preparations had a wide range (0.005 to 0.19) of CO3/Ca molar ratios that bracket the ratios found in porcine enamel mineral at various developmental stages. Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction analyses showed that the calcium apatites precipitating at neutral pH incorporated the carbonate into both the hydroxyl and phosphate ion sites in their lattices (A,B-types), whereas the preparations made at the alkaline pH (high OH-(-)CO3(2-)-competition) or in the presence of fluoride (F-(-)CO3(2-) competition) yielded only the B-type carbonato-apatite. It was also ascertained that the size and morphology of the carbonato-apatites, assessed by specific surface area determination and high-resolution electron microscopy, were highly dependent on the driving force for precipitation and the presence of regulators (CO3(2-) and F-) in solution. In neutral media, early precipitates were thin-ribbon in appearance, but grew into crystals having flattened-hexagonal cross-sections. In the presence of fluoride or in alkaline media, acicular apatite crystals, precipitated initially, grew into large rod-like carbonato-apatites having a symmetric-hexagonal cross-section. In both neutral and alkaline solutions, carbonate inhibited the growth of apatite crystals along their c axis, leading to the formation of bulkier crystals. The formation of carbonato-apatites at the neutral pH and their properties are consistent with observations made on enamel minerals formed in the early developmental stages.
牙釉质矿物质的组成与碳酸钙磷灰石的组成相对应。为了深入了解具有特定性质（晶体尺寸、形态以及碳酸根掺入晶格）的碳酸磷灰石的沉淀过程，在80摄氏度下于具有不同碳酸根浓度且pH值约为7.5或10.5（±0.5）的水体系中制备了磷灰石。各种制备物的碳酸根/钙摩尔比范围很广（0.005至0.19），涵盖了猪牙釉质矿物质在不同发育阶段所发现的比例。傅里叶变换红外光谱（FTIR）和X射线衍射分析表明，在中性pH下沉淀的钙磷灰石将碳酸根掺入其晶格中的羟基和磷酸根离子位点（A、B型），而在碱性pH（高氢氧根-碳酸根竞争）或存在氟化物（氟-碳酸根竞争）的情况下制备的产物仅产生B型碳酸磷灰石。还确定了通过比表面积测定和高分辨率电子显微镜评估的碳酸磷灰石的尺寸和形态高度依赖于沉淀驱动力以及溶液中调节剂（碳酸根和氟）的存在。在中性介质中，早期沉淀物外观呈细带状，但会生长成具有扁平六边形横截面的晶体。在存在氟化物或碱性介质中，最初沉淀的针状磷灰石晶体会生长成具有对称六边形横截面的大棒状碳酸磷灰石。在中性和碱性溶液中，碳酸根均抑制磷灰石晶体沿其c轴生长，导致形成更粗大的晶体。在中性pH下碳酸磷灰石的形成及其性质与在发育早期形成的牙釉质矿物质的观察结果一致。
