The Study of Craniomandibular Disorder Using MRI, Three-Dimensional Bite Force and EMG.

颅下颌关节紊乱（CMD）是一种发生在咀嚼肌和颞下颌关节（TMJ）上的功能障碍，因此需要对口腔系统的正常功能进行详细的研究。肌肉的取向和附着等形态学参数影响肌肉的活动和TMJ的内应力。因此，结合面部形态学分析咀嚼肌的功能就显得尤为重要。首先，在三维调节咬合力的条件下，对正常被试咬合时的咬肌和颞肌的肌表电图进行编码和分析，找出咀嚼肌的协调模式。因此，当咬合力在前、后、侧方向发生变化时，两块肌肉的活动会发生相反的变化。也就是说，这些肌肉在咬合力方向的变化中明显表现出相互激活的模式。由于咬肌具有复杂的层状结构和组织化学异质性肌纤维，因此对其各部位的功能进行了研究。基于三维咬合力和运动单元同时记录的研究表明，每个运动单元都有特定的最佳射击方向范围，咬肌的每个部分在其功能中发挥不同的作用。这可能反映了咬肌的分层结构，因为咬肌前后部的功能差异比内外部和外部的差异更明显。此外，我们还使用侧位颅面造影进行形态学分析，以探讨咀嚼肌协调模式与面部形态之间的关系。虽然咬肌和颞肌的协调模式在受试者中几乎相同，但它们的活动似乎受到下颌平面倾角等形态学因素的影响。目前的研究揭示了咬肌和颞肌的协调模式以及咬肌各部分的作用，但面部形态与它们的关系没有得到充分的解释。对口颌系统进行生物力学分析是研究口颌系统的必要条件，其中形态和功能研究尤为重要。少

Detailcd study normal function of stomatognathic system is needcd to investigate the nature of craniomandibular disorder (CMD) because it is the dysfunction found in masticatoty muscles and temporomandibular joint (TMJ). Morphological parameters such as orientation and attachment of muscles affect the activities of muscles and internal stress of TMJ. Then it is much important to analyze the function of masticatory muscles with refercnce to facial morphology.At first, to find the coordination pattern of masticatory muscles, surface electromyograms (EMGs) of masseter and temporal muscles were recoded and analyzed when normal subjects were asked to clench on condition that their bite force were regulated three-dimensionally. As s result, when bite force changed anteriorly, posteriorly and laterally, the activities of two muscles changed in reverse manners each other. Namely it became apparent that these muscles showed reciprocal activation pattern in the changes of bite force direction.Co … More ntinuously different functions of each part of masseler muscle were investigated since it had complex layering structure histochemically heterogeneous muscle fibers. The study based on simultaneous recording of three-dimensional bite force and motor units made clear that each motor unit had a specific optimal directional range for its firing and each part of masseter muscle played a different role for its function. It was suggested that this reflected the layering structure of masseter muscle because the difference of function was more markedly between anterior and posterior parts than between internal and external and external parts.In addition, a morphological analysis using lateral rentogenographic cephalograms were performed to investigate the relationships between the coordination pattern of masticatory muscles and facial morphology. Though the coordination patter of masseter and lemporal museles were almost same among subjects, activities of each were seemed to be affected by some morphological factors such as an inclination of mandibular plane.The present study revealed the coordination pattern of masseter and temporal muscles and the role of each part of masseter muscle but the relations of facial morphology to them were not sufficiently explained. Biomechanical analyses of stomatognathic system are necessary for studying the CMD, and it is evident that morphological and functional investigations are important. Less