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

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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