Porro Laura B, Holliday Casey M, Anapol Fred, Ontiveros Lupita C, Ontiveros Lolita T, Ross Callum F
Department of Organismal Biology and Anatomy, University of Chicago, Illinois 60637, USA.
J Morphol. 2011 Aug;272(8):910-37. doi: 10.1002/jmor.10957. Epub 2011 May 12.
The mechanical behavior of mammalian mandibles is well-studied, but a comprehensive biomechanical analysis (incorporating detailed muscle architecture, accurate material properties, and three-dimensional mechanical behavior) of an extant archosaur mandible has never been carried out. This makes it unclear how closely models of extant and extinct archosaur mandibles reflect reality and prevents comparisons of structure-function relationships in mammalian and archosaur mandibles. We tested hypotheses regarding the mechanical behavior of the mandible of Alligator mississippiensis by analyzing reaction forces and bending, shear, and torsional stress regimes in six models of varying complexity. Models included free body analysis using basic lever arm mechanics, 2D and 3D beam models, and three high-resolution finite element models of the Alligator mandible, incorporating, respectively, isotropic bone without sutures, anisotropic bone with sutures, and anisotropic bone with sutures and contact between the mandible and the pterygoid flange. Compared with the beam models, the Alligator finite element models exhibited less spatial variability in dorsoventral bending and sagittal shear stress, as well as lower peak values for these stresses, suggesting that Alligator mandibular morphology is in part designed to reduce these stresses during biting. However, the Alligator models exhibited greater variability in the distribution of mediolateral and torsional stresses than the beam models. Incorporating anisotropic bone material properties and sutures into the model reduced dorsoventral and torsional stresses within the mandible, but led to elevated mediolateral stresses. These mediolateral stresses were mitigated by the addition of a pterygoid-mandibular contact, suggesting important contributions from, and trade-offs between, material properties and external constraints in Alligator mandible design. Our results suggest that beam modeling does not accurately represent the mechanical behavior of the Alligator mandible, including important performance metrics such as magnitude and orientation of reaction forces, and mediolateral bending and torsional stress distributions. J.Morphol. 2011. © 2011 Wiley-Liss, Inc.
哺乳动物下颌骨的力学行为已得到充分研究，但对于现存主龙类下颌骨的全面生物力学分析（包括详细的肌肉结构、准确的材料特性和三维力学行为）却从未进行过。这使得现存和已灭绝主龙类下颌骨模型与现实的贴合程度尚不清楚，并阻碍了对哺乳动物和主龙类下颌骨结构 - 功能关系的比较。我们通过分析六种不同复杂程度模型中的反作用力以及弯曲、剪切和扭转应力状态，对密西西比鳄下颌骨的力学行为假设进行了测试。模型包括使用基本杠杆臂力学的自由体分析、二维和三维梁模型，以及三个密西西比鳄下颌骨的高分辨率有限元模型，分别纳入了无缝合线的各向同性骨、有缝合线的各向异性骨，以及有缝合线且下颌骨与翼状突缘之间有接触的各向异性骨。与梁模型相比，密西西比鳄有限元模型在背腹向弯曲和矢状面剪切应力方面表现出较小的空间变异性，并且这些应力的峰值也较低，这表明密西西比鳄下颌骨形态在一定程度上是为了在咬合过程中降低这些应力而设计的。然而，密西西比鳄模型在内外侧和扭转应力分布上比梁模型表现出更大的变异性。将各向异性骨材料特性和缝合线纳入模型可降低下颌骨内的背腹向和扭转应力，但会导致内外侧应力升高。通过增加翼状突 - 下颌接触可减轻这些内外侧应力，这表明材料特性和外部约束在密西西比鳄下颌骨设计中具有重要作用且存在权衡。我们的结果表明，梁模型不能准确代表密西西比鳄下颌骨的力学行为，包括反作用力的大小和方向以及内外侧弯曲和扭转应力分布等重要性能指标。《形态学杂志》。2011年。©2011威利 - 利斯公司。
