Langenbach G E, Hannam A G
Department of Oral Health Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, Canada.
Arch Oral Biol. 1999 Jul;44(7):557-73. doi: 10.1016/s0003-9969(99)00034-5.
The role of passive muscle tensions in human jaw function are largely unknown. It seems reasonable to assume that passive muscle-tension properties are optimized for the multiple physiological tasks the jaw performs in vivo. However, the inaccessibility of the jaw muscles is a major obstacle to measuring their passive tensions, and understanding their effects. Computer modelling offers an alternative method for doing this. Here, a three-dimensional, dynamic model was used to predict active and passive jaw-muscle tensions during simulated postural rest, jaw opening and chewing. The model included a rigid mandible, two temporomandibular joints, multiple dental bite points, and an artificial food bolus located between the right first molars. It was driven by 18 Hill-type actuators representing nine pairs of jaw muscles. All anatomical forms, positions and properties used in the model were based on previously published, average values. Two states were stimulated, one in which all optimal lengths for the length-tension curves in the closing muscles were defined as their fibre-component lengths when the incisor teeth were 2 mm apart (S2), and another in which the optimal lengths were set for a 12.0 mm interincisal separation (S12). At rest, the jaw attained 3.6 mm interincisal separation in S2, and 14.8 mm in S12. Activation of the inferior lateral pterygoid (ILP) and digastric (DG) muscles in various combinations always induced passive jaw-closer tensions, and compressive condylar loads. Maximum midline gape (from maximum bilateral co-activation of DG and ILP) was 16.2 mm in S2, and 32.0 mm in S12. When both model states were driven with muscle patterns typical for human mastication, recognizable unilateral and vertical "chopping" chewing cycles were produced. Both states revealed condylar loading in the opening and closing phases of mastication. During unilateral chewing, compressive force on the working-side condyle exceeded that on the balancing side. In contrast, during the "chopping" cycle, loading on the balancing side was greater than that on the working side. In S2, chewing was limited in both vertical and lateral directions. These results suggest that the assumptions used in S12 more closely approximated human behaviour than those in S2. Despite its limitations, modelling appears to provide a useful conceptual framework for developing hypotheses regarding the role of muscle tensions during human jaw function.
被动肌肉张力在人类下颌功能中的作用在很大程度上尚不明确。假定被动肌肉张力特性针对下颌在体内执行的多种生理任务进行了优化似乎是合理的。然而，下颌肌肉难以触及是测量其被动张力以及了解其作用的主要障碍。计算机建模提供了一种替代方法来实现这一点。在此，使用了一个三维动态模型来预测模拟姿势休息、张口和咀嚼过程中主动和被动的下颌肌肉张力。该模型包括一个刚性下颌骨、两个颞下颌关节、多个牙咬合点以及位于右侧第一磨牙之间的人工食团。它由代表九对下颌肌肉的18个希尔型驱动器驱动。模型中使用的所有解剖形态、位置和特性均基于先前发表的平均值。模拟了两种状态，一种状态下，当切牙间距为2毫米时，闭合肌肉长度 - 张力曲线的所有最佳长度被定义为其纤维成分长度（S2），另一种状态下，切牙间分离设定为12.0毫米时设定最佳长度（S12）。在休息时，下颌在S2状态下切牙间分离达到3.6毫米，在S12状态下达到14.8毫米。翼外肌下头（ILP）和二腹肌（DG）肌肉以各种组合激活时，总会诱发被动的下颌闭合肌张力以及髁突压缩负荷。最大中线开口度（来自DG和ILP的最大双侧共同激活）在S2状态下为16.2毫米，在S12状态下为32.0毫米。当两种模型状态都由典型的人类咀嚼肌肉模式驱动时，会产生可识别的单侧和垂直“切碎”咀嚼周期。两种状态在咀嚼的开口和闭合阶段均显示出髁突负荷。在单侧咀嚼时，工作侧髁突上的压缩力超过平衡侧。相反，在“切碎”周期中，平衡侧的负荷大于工作侧。在S2状态下，咀嚼在垂直和侧向方向上都受到限制。这些结果表明，S12中使用的假设比S2中的假设更接近人类行为。尽管存在局限性，但建模似乎为提出关于人类下颌功能中肌肉张力作用的假设提供了一个有用的概念框架。
