Ichim I, Swain M V, Kieser J A
Department of Oral Sciences, Faculty of Dentistry, University of Otago, New Zealand.
J Biomech. 2006;39(10):1903-13. doi: 10.1016/j.jbiomech.2005.05.022. Epub 2005 Aug 8.
The chin is a feature unique to humans. This study evaluates the effect of mandibular symphyseal design on biomechanical masticatory effectiveness as determined by structural stiffness and stress developed under flexural and torsional loading. A simple model of three symphyseal shapes (chin, flat symphysis and lingual buttress), was built to represent human, Neanderthal and higher primate symphyses and these were subjected to wishboning and torsional forces. Additionally, an anatomically detailed reconstruction was made of the CT scan of an actual human mandible, which was then also morphed into a chinless model. The results of a 3-D finite element analysis show firstly, that none of the three different symphyseal shapes is biomechanically more advantageous than the others for the given loading condition. Secondly, we show in a CT-derived model, that the presence of a chin does not confer significantly improved stiffness to torsional or flexural loading. These results indicate that the acquisition of a chin in modern humans is not related to the functional demands placed upon the mandible during mastication, but suggest that it may have developed in response to other biomechanical demands.
下巴是人类独有的特征。本研究评估了下颌联合设计对生物力学咀嚼效能的影响，该效能由弯曲和扭转载荷下产生的结构刚度和应力决定。构建了三种联合形状（下巴、扁平联合和舌侧支柱）的简单模型，以代表人类、尼安德特人和高等灵长类动物的联合，对其施加叉状张开和扭转载荷。此外，对实际人类下颌骨的CT扫描进行了详细的解剖学重建，然后将其变形为无下巴模型。三维有限元分析结果首先表明，对于给定的加载条件，三种不同的联合形状在生物力学上都不比其他形状更具优势。其次，我们在CT衍生模型中表明，下巴的存在并不会显著提高对扭转载荷或弯曲载荷的刚度。这些结果表明，现代人类下巴的形成与咀嚼过程中下颌骨所承受的功能需求无关，但表明它可能是为响应其他生物力学需求而发展形成的。
