Daegling David J, Hotzman Jennifer L
Department of Anthropology, University of Florida, Gainesville, Florida 32611-7305, USA.
Am J Phys Anthropol. 2003 Sep;122(1):38-50. doi: 10.1002/ajpa.10225.
Local variation in cortical bone thickness in the postcanine mandibular corpus appears to be stereotypical among anthropoids. Specifically, at sections under the molars, lingually situated cortical bone is typically thinner than that along the lateral aspect. This pattern applies despite phylogenetic, dietary, and allometric differences among the anthropoids sampled to date. Demes et al. (Food Acquisition and Processing in Primates [1984] New York: Plenum Press, p. 369-390) employed a theoretical analysis of mastication in Gorilla and Homo to argue that this pattern could be explained with reference to biomechanical stresses. Specifically, they proposed that the combined effects of torsion and direct shear on the working-side corpus create a condition in which net stresses and strains are reduced along the lingual cortical plate. Demonstration of this effect would suggest a functional linkage between localized differences in bone mass and strain gradients in the facial skeleton. We conducted an empirical evaluation of the effects of the combined loads of torsion and direct shear in vitro on a sample of formalin-fixed human mandibles. Rosette strain gages were affixed to the lateral and medial aspects of the corpus in each specimen, and surface strains were recorded separately under controlled torsional and occlusal loads, and under simultaneous application of these loads. The hypothesis that lingual strains are reduced under combined twisting and occlusal loads was generally supported; however, we observed reduction in surface strains at some sites along the lateral aspect of the corpus under these combined loads as well. These unexpected findings are attributable to unanticipated loading conditions imposed by occlusal forces, which result from sources of stress in addition to direct shear. These experiments provide provisional support for the hypothesis that superposed sources of bone strain produce large strain gradients between buccal and lingual aspects of the mandibular corpus, and that local variation in bone mass may be associated with these gradients.
犬齿后下颌体皮质骨厚度的局部差异在类人猿中似乎是固定不变的。具体而言，在磨牙下方的切片中，舌侧的皮质骨通常比外侧的薄。尽管迄今为止所采样的类人猿在系统发育、饮食和异速生长方面存在差异，但这种模式依然适用。德姆斯等人（《灵长类动物的食物获取与加工》[1984年]，纽约：普伦蒂斯出版社，第369 - 390页）对大猩猩和人类的咀嚼进行了理论分析，认为这种模式可以用生物力学应力来解释。具体来说，他们提出工作侧下颌体上扭转和直接剪切的联合作用产生了一种情况，即舌侧皮质板上的净应力和应变会减小。这种效应的证明将表明骨量的局部差异与面部骨骼应变梯度之间存在功能联系。我们对福尔马林固定的人类下颌骨样本进行了体外扭转和直接剪切联合载荷效应的实证评估。在每个标本的下颌体外侧和内侧粘贴应变片，分别在受控的扭转和咬合载荷下以及同时施加这些载荷时记录表面应变。舌侧应变在扭转和咬合联合载荷下会减小这一假设总体上得到了支持；然而，我们也观察到在这些联合载荷下，下颌体外侧某些部位的表面应变也有所减小。这些意外发现归因于咬合力施加的意外载荷条件，咬合力除了直接剪切外还源于其他应力源。这些实验为以下假设提供了初步支持：叠加的骨应变源在下颌体颊侧和舌侧之间产生大的应变梯度，并且骨量的局部差异可能与这些梯度有关。
