Lee D D
Harvard School of Dental Medicine, Department of Oral Biology and Ultrastructure, Boston, MA 02115.
J Microsc. 1989 Jun;154(Pt 3):209-14. doi: 10.1111/j.1365-2818.1989.tb00583.x.
Lattice imperfections in the structure of shark (Nataprion brevirostrais) enamel crystallites have been studied by means of lattice-imaging in a high-resolution transmission electron microscope. Line defects exhibiting various lengths (100-2500 A) and widths (10-30 A) and demonstrating phase behaviour different from that of the host crystal were observed along the fringes representing (100) lattice planes. When defect sites were subjected to an electron beam, an annealing process was observed in which the difference in phase contrast eventually disappeared and the defect itself became an intricate part of the (100)-type lattice planes. A through-focal series of the defects show a reversal in phase contrast. By examining the contrast behaviour under certain focal conditions and by adopting the Fresnel diffraction mode, the refractive index of the defect regions was determined to be lower than that of the apatite crystal. Present findings suggest that the interlayering structure along the (100) planes is responsible for the line defects observed in enamel apatites.
通过高分辨率透射电子显微镜中的晶格成像技术，对鲨鱼（窄头双髻鲨）牙釉质微晶结构中的晶格缺陷进行了研究。沿着代表（100）晶格平面的条纹观察到了线缺陷，这些线缺陷呈现出不同的长度（100 - 2500 Å）和宽度（10 - 30 Å），并且表现出与主体晶体不同的相行为。当缺陷部位受到电子束照射时，观察到了一个退火过程，在此过程中，相衬度的差异最终消失，缺陷本身成为了（100）型晶格平面的一个复杂部分。对缺陷进行的一系列聚焦观察显示相衬度发生了反转。通过在特定聚焦条件下检查相衬行为并采用菲涅耳衍射模式，确定缺陷区域的折射率低于磷灰石晶体的折射率。目前的研究结果表明，沿（100）平面的层间结构是牙釉质磷灰石中观察到的线缺陷的原因。
