The radula, a chitinous membrane with embedded teeth, is one important molluscan autapomorphy. In some taxa (Polyplacophora and Patellogastropoda) one tooth type (the dominant lateral tooth) was studied intensively in the last decades with regard to its mechanical properties, chemical and structural composition, and the relationship between these parameters. As the dominant lateral tooth is probably one of the best studied biological materials, it is surprising, that data on elements and mechanical properties of the other tooth types, present on a chiton radula, is lacking. We provide data on the elemental distribution and mechanical properties (hardness and elasticity, i.e. Young’s modulus) of all teeth from the Polyplacophora Lepidochitona cinerea (Linnaeus, 1767) [Chitonidae: Ischnochitonidae]. The ontogeny of elements, studied by energy-dispersive X-ray spectroscopy, and of the mechanical properties, determined by nanoindentation, was analysed in every individual tooth type. Additionally, we performed breaking stress experiments with teeth under dry and wet condition, highlighting the high influence of the water content on the mechanical behaviour of the radula. We thereby could determine the forces and stresses, teeth can resist, which were previously not studied in representatives of Polyplacophora. Overall, we were able to relate the mineral (iron, calcium) content with the mechanical parameters (hardness and Young’s modulus) and the breaking force and stress in every tooth type. This led to a better understanding of the relationship between structure, material, and function in radular teeth. Further, we aimed at determining the role of calcium for the mechanical behaviour of the teeth: we decalcified radulae by ethylene diamine tetra acetic acid and performed afterwards elemental analyses, breaking stress experiments, and nanoindentation. Among other things, we detected that wet and decalcified radular teeth could resist highest forces, since teeth have a higher range of bending motion leading to a higher capability of teeth to gain mechanical support from the adjacent tooth row. This indicates, that the tooth material is the result of a compromise between failure reduction and the ability to transfer forces onto the ingesta. We present novel data on the elemental composition, mechanical properties, and the mechanical behaviour of chiton teeth, which allows conclusions about tooth function. We could also relate the parameters mentioned, which contributes to our understanding on the origins of mechanical property gradients and the processes reducing structural failure in radular teeth. Additionally, we add more evidence, that the elemental composition of radular is probably species-specific and could be used as taxonomic character.

中文翻译：

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石鳖 Lepidochitona cinerea 齿的元素组成和生物力学的个体发育

齿舌是一种嵌有牙齿的几丁质膜，是一种重要的软体动物自体。在一些分类群（Polyplacophora 和 Patellogastropoda）中，在过去的几十年中，就其机械性能、化学和结构组成以及这些参数之间的关系，对一种牙齿类型（主要侧牙）进行了深入研究。由于主要的侧牙可能是研究得最好的生物材料之一，令人惊讶的是，缺乏关于存在于石鳖齿上的其他牙齿类型的元素和机械性能的数据。我们提供了Polyplacophora Lepidochitona cinerea (Linnaeus, 1767) [Chitonidae: Ischnochitonidae]所有牙齿的元素分布和机械性能（硬度和弹性，即杨氏模量）的数据。元素的个体发育，通过能量色散 X 射线光谱学研究，并分析了通过纳米压痕确定的机械性能，并对每种牙齿类型进行了分析。此外，我们在干燥和潮湿条件下对牙齿进行了断裂应力实验，突出了含水量对齿舌机械行为的高度影响。因此，我们可以确定牙齿可以抵抗的力和应力，这是以前没有在 Polyplacophora 的代表中研究过的。总体而言，我们能够将矿物质（铁、钙）含量与机械参数（硬度和杨氏模量）以及每种牙齿类型的断裂力和应力联系起来。这使我们更好地理解了齿形牙齿的结构、材料和功能之间的关系。更远，我们的目标是确定钙对牙齿机械行为的作用：我们用乙二胺四乙酸对牙根进行脱钙，然后进行元素分析、断裂应力实验和纳米压痕。除其他外，我们检测到潮湿和脱钙的齿状牙齿可以抵抗最高的力，因为牙齿具有更大范围的弯曲运动，从而导致牙齿从相邻牙齿排获得机械支撑的能力更高。这表明，牙齿材料是在减少故障和将力传递到摄取物上的能力之间折衷的结果。我们提供关于石鳖牙齿的元素组成、机械性能和机械行为的新数据，从而得出关于牙齿功能的结论。我们还可以关联提到的参数，这有助于我们理解机械性能梯度的起源和减少辐射状牙齿结构失效的过程。此外，我们添加了更多证据，表明 radular 的元素组成可能是物种特异性的，可以用作分类特征。