Geerinckx Tom, Huysseune Ann, Boone Matthieu, Claeys Myriam, Couvreur Marjolein, De Kegel Barbara, Mast Peter, Van Hoorebeke Luc, Verbeken Kim, Adriaens Dominique
Evolutionary Morphology of Vertebrates, Ghent University, K. L. Ledeganckstraat 35, 9000 Ghent, Belgium.
Physiol Biochem Zool. 2012 Sep-Oct;85(5):481-90. doi: 10.1086/667532. Epub 2012 Aug 3.
Teeth are generally used for actions in which they experience mainly compressive forces acting toward the base. The ordered tooth enamel(oid) and dentin structures contribute to the high compressive strength but also to the minor shear and tensile strengths. Some vertebrates, however, use their teeth for scraping, with teeth experiencing forces directed mostly normal to their long axis. Some scraping suckermouth catfishes (Loricariidae) even appear to have flexible teeth, which have not been found in any other vertebrate taxon. Considering the mineralized nature of tooth tissues, the notion of flexible teeth seems paradoxical. We studied teeth of five species, testing and measuring tooth flexibility, and investigating tooth (micro)structure using transmission electron microscopy, staining, computed tomography scanning, and scanning electron microscopy-energy-dispersive spectrometry. We quantified the extreme bending capacity of single teeth (up to 180°) and show that reorganizations of the tooth (micro)structure and extreme hypomineralization of the dentin are adaptations preventing breaking by allowing flexibility. Tooth shape and internal structure appear to be optimized for bending in one direction, which is expected to occur frequently when feeding (scraping) under natural conditions. Not all loricariid catfishes possess flexible teeth, with the trait potentially having evolved more than once. Flexible teeth surely rank among the most extreme evolutionary novelties in known mineralized biological materials and might yield a better understanding of the processes of dentin formation and (hypo)mineralization in vertebrates, including humans.
牙齿通常用于主要承受朝向牙根的压缩力的动作。有序排列的牙釉质（类）和牙本质结构不仅有助于高抗压强度，也有助于较小的抗剪切和抗拉伸强度。然而，一些脊椎动物用它们的牙齿进行刮擦，牙齿承受的力大多垂直于其长轴。一些刮食的吸口鲶鱼（甲鲶科）甚至似乎有灵活的牙齿，这在其他任何脊椎动物分类群中都未发现。考虑到牙齿组织的矿化性质，灵活牙齿的概念似乎自相矛盾。我们研究了五个物种的牙齿，测试和测量了牙齿的柔韧性，并使用透射电子显微镜、染色、计算机断层扫描和扫描电子显微镜 - 能量色散光谱法研究了牙齿（微观）结构。我们量化了单个牙齿的极端弯曲能力（高达180°），并表明牙齿（微观）结构的重组和牙本质的极端低矿化是通过允许柔韧性来防止断裂的适应性变化。牙齿的形状和内部结构似乎是为了在一个方向上弯曲而优化的，在自然条件下进食（刮擦）时预计会经常出现这种情况。并非所有甲鲶科鲶鱼都有灵活的牙齿，这种特征可能已经进化了不止一次。灵活的牙齿肯定是已知矿化生物材料中最极端的进化新奇事物之一，可能会让我们更好地理解包括人类在内的脊椎动物牙本质形成和（低）矿化的过程。
