Anderson Philip S L, Gill Pamela G, Rayfield Emily J
Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK.
J Morphol. 2011 Jan;272(1):50-65. doi: 10.1002/jmor.10896. Epub 2010 Oct 19.
The mammalian cingulum is a shelf of enamel, which rings the base of the molar crown (fully or partially). Certain nonmammalian cynodonts show precursors of this structure, indicating that it may be an important dental character in the origins of mammals. However, there is little consensus as to what drove the initial evolution of the cingulum. Recent work on physical modeling of fracture mechanics has shown that structures which approximate mammalian dentition (hard enamel shell surrounding a softer/tougher dentine interior) undergo specific fracture patterns dependent on the material properties of the food items. Soft materials result in fractures occurring at the base of the stiff shell away from the contact point due to heightened tensile strains. These tensile strains occur around the margin in the region where cingula develop. In this article, we test whether the presence of a cingulum structure will reduce the tensile strains seen in enamel using basic finite element models of bilayered cones. Finite element models of generic cone shaped "teeth" were created both with and without cingula of various shapes and sizes. Various forces were applied to the models to examine the relative magnitudes and directions of average maximum principal strain in the enamel. The addition of a cingulum greatly reduces tensile strains in the enamel caused by "soft-food" forces. The relative shape and size of the cingulum has a strong effect on strain magnitudes as well. Scaling issues between shapes are explored and show that the effectiveness of a given cingulum to reducing tensile strains is dependent on how the cingulum is created. Partial cingula, which only surround a portion of the tooth, are shown to be especially effective at reducing strain caused by asymmetrical loads, and shed new light on the potential early function and evolution of mammalian dentitions.
哺乳动物的齿带是一层釉质，它环绕着磨牙牙冠的基部（完全或部分环绕）。某些非哺乳动物的犬齿兽类显示出这种结构的前身，这表明它可能是哺乳动物起源中的一个重要牙齿特征。然而，关于是什么驱动了齿带的最初进化，几乎没有达成共识。最近关于断裂力学物理建模的研究表明，近似哺乳动物牙列的结构（坚硬的釉质外壳包围着较软/较坚韧的牙本质内部）会根据食物的材料特性经历特定的断裂模式。软质材料会由于拉伸应变增加而导致在坚硬外壳的基部远离接触点处发生断裂。这些拉伸应变发生在齿带发育区域的边缘周围。在本文中，我们使用双层锥体的基本有限元模型来测试齿带结构的存在是否会减少釉质中出现的拉伸应变。创建了具有各种形状和尺寸的带齿带和不带齿带的通用锥形“牙齿”的有限元模型。对模型施加各种力，以检查釉质中平均最大主应变的相对大小和方向。添加齿带极大地减少了由“软食物”力引起的釉质中的拉伸应变。齿带的相对形状和大小对应变大小也有很大影响。探索了不同形状之间的比例问题，结果表明给定齿带减少拉伸应变的有效性取决于齿带的创建方式。仅围绕牙齿一部分的部分齿带在减少不对称载荷引起的应变方面特别有效，这为哺乳动物牙列的潜在早期功能和进化提供了新的线索。
