Institute of Inorganic Chemistry and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen, Universitaetsstr. 5-7, 45117 Essen, Germany.
J Struct Biol. 2012 Jun;178(3):290-9. doi: 10.1016/j.jsb.2012.03.012. Epub 2012 Apr 5.
The teeth of two different shark species (Isurus oxyrinchus and Galeocerdo cuvier) and a geological fluoroapatite single crystal were structurally and chemically characterized. In contrast to dentin, enameloid showed sharp diffraction peaks which indicated a high crystallinity of the enameloid. The lattice parameters of enameloid were close to those of the geological fluoroapatite single crystal. The inorganic part of shark teeth consisted of fluoroapatite with a fluoride content in the enameloid of 3.1 wt.%, i.e., close to the fluoride content of the geological fluoroapatite single crystal (3.64 wt.%). Scanning electron micrographs showed that the crystals in enameloid were highly ordered with a special topological orientation (perpendicular towards the outside surface and parallel towards the center). By thermogravimetry, water, organic matrix, and biomineral in dentin and enameloid of both shark species were determined. Dentin had a higher content of water, organic matrix, and carbonate than enameloid but contained less fluoride. Nanoindentation and Vicker's microhardness tests showed that the enameloid of the shark teeth was approximately six times harder than the dentin. The hardness of shark teeth and human teeth was comparable, both for dentin and enamel/enameloid. In contrast, the geological fluoroapatite single crystal was much harder than both kinds of teeth due to the absence of an organic matrix. In summary, the different biological functions of the shark teeth ("tearing" for Isurus and "cutting" for Galeocerdo) are controlled by the different geometry and not by the chemical or crystallographic composition.
对两种不同鲨鱼物种（长尾鲨和灰鲭鲨）的牙齿和一个地质氟磷灰石单晶进行了结构和化学特性分析。与牙本质相比，釉质表现出尖锐的衍射峰，表明釉质具有较高的结晶度。釉质的晶格参数接近地质氟磷灰石单晶的晶格参数。鲨鱼牙齿的无机部分由氟磷灰石组成，其中釉质中的氟含量为 3.1wt.%，即接近地质氟磷灰石单晶的氟含量（3.64wt.%）。扫描电子显微镜图像显示，釉质中的晶体具有高度有序的特殊拓扑取向（垂直于外表面，平行于中心）。通过热重分析，确定了两种鲨鱼牙齿的牙本质和釉质中的水、有机基质和生物矿物。牙本质中的水、有机基质和碳酸盐含量高于釉质，但氟含量较低。纳米压痕和维氏硬度测试表明，鲨鱼牙齿的釉质硬度约为牙本质的六倍。鲨鱼牙齿和人类牙齿的硬度相当，无论是牙本质还是牙釉质/釉质。相比之下，由于缺乏有机基质，地质氟磷灰石单晶比两种牙齿都要硬得多。总之，鲨鱼牙齿的不同生物学功能（“撕裂”用长尾鲨和“切割”用灰鲭鲨）是由不同的几何形状控制的，而不是由化学成分或结晶度控制的。
