Hylander W L
Am J Phys Anthropol. 1975 Sep;43(2):227-42. doi: 10.1002/ajpa.1330430209.
The mammalian mandible, and in particular the human mandible, is generally thought to function as a lever during biting. This notion, however, has not gone unchallenged. Various workers have suggested that the mandible does not function as a lever, and they base this proposition on essentially two assertions: (1) the resultant of the forces produced by the masticatory muscles always passes through the bite point; (2) the condylar neck and/or the temporomandibular joint is unsuited to withstand reaction forces during biting. A review of the electromyographic data and of the properties of the tissues of the temporomandibular joint do not support the non-lever hypothesis of mandibular function. In addition, an analysis of the strength of the condylar neck demonstrates that this structure is strong enough to withstand the expected reaction force during lever action. Ordinarily the human mandible and the forces that act upon it are analyzed solely in the lateral projection. Moments are then usually analyzed about the mandibular condyle; however, some workers have advocated taking moments about other points, e.g., the instantaneous center of rotation. Obviously it makes no difference as to what point is chosen since the moments about any point during equilibrium conditions are equal to zero. It is also useful to analyze the forces acting on the mandible in the frontal projection, particularly during unilateral biting. The electromyographic data suggest that during powerful unilateral molar biting the resultant adductor muscle force is passing between the bite point and the balancing (non-biting side) condyle. Therefore, in order for this system to be in equilibrium there must be a reaction force acting on the balancing condyle. This suggests that reaction forces are larger on the balancing side than on the working side, and possibly explains why individuals with a painful temporomandibular joint usually prefer to bite on the side of the diseased joint.
哺乳动物的下颌骨，尤其是人类的下颌骨，通常被认为在咬合过程中起到杠杆的作用。然而，这一观点并非没有受到质疑。许多研究人员认为下颌骨并非起到杠杆的作用，他们提出这一观点主要基于两个论断：（1）咀嚼肌产生的合力总是通过咬合点；（2）髁突颈部和/或颞下颌关节不适合承受咬合时的反作用力。对肌电图数据以及颞下颌关节组织特性的回顾并不支持下颌骨功能的非杠杆假说。此外，对髁突颈部强度的分析表明，该结构足够坚固，能够承受杠杆作用期间预期的反作用力。通常，人类下颌骨及其所受的力仅在侧位投影中进行分析。然后通常围绕下颌髁突分析力矩；然而，一些研究人员主张围绕其他点分析力矩，例如瞬时旋转中心。显然，选择哪个点并无差异，因为在平衡状态下围绕任何点的力矩都等于零。在额状位投影中分析作用于下颌骨的力也很有用，尤其是在单侧咬合时。肌电图数据表明，在强力单侧磨牙咬合过程中，内收肌合力通过咬合点和平衡（非咬合侧）髁突之间。因此，为了使该系统处于平衡状态，必须有一个反作用力作用于平衡髁突。这表明平衡侧的反作用力比工作侧的更大，这可能解释了为什么颞下颌关节疼痛的个体通常更喜欢在患病关节一侧咬合。
