DEVELOPMENT OF METHOD FOR DETERMINING MANDIBULAR POSITION IN EDENTULOUS PATIENTS WITH DIFFICULTIES.

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Of the various methods in the assessment of correct vertical jaw relations, the comfortable zone (CZ) and the most comfortable position (MCP) are noteworthy because it utilizes proprioceptive sensations inherent to the subject. It is unknown whether or not the vertical dimension determined by this method is acceptable from a physiological point of view.For evaluation of the MCP in edentulous subjects, the MCP was recorded in ten edentulous subjects and compared with the intercuspal position (ICP) of normal dentulous people by cephalometric analysis. It was found that the MCP was at a lower mandibular position than the ICP because the facial height was markedly reduced with a front-upward rotation of the mandible centering around the condyles. Thus, it has been suggested that the occlusal vertical dimension (OVD) of the MCP in the restored dentition is less than that of the original ICP.Furthermore we evaluated the CZ and MCP from a physiological or functional point of view using bite force and EMG recording measurements. Analysis of the relationship between vertical dimension and bite force or EMG activities of jaw-closing muscles is one of the most important and basic evaluation techniques of stomatognathic function. The MCP does not exist at any specific point, but in the range where the bite force markedly changed with an increase in vertical dimension, compared to the ICP of healthy dentulous subjects. These results suggested that the MCP of edentulous subjects corresponded with the ICP of dentulous subjects from a functional point of view. The condition of healthy dentulous subjects is considered a universal standard. Therefore, the MCP is physiologically acceptable.The OVD of the MCP may be established at a lower vertical dimension after teeth loss, and positioned in a similar functional position as the ICP of healthy subjects.