The Attachment of the Masseter Muscle Influences of the Craniofacial Morphology and Bite Force Distribution

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This research is divided into three sections as follows ;1. The relationship between masseter muscle and craniofacial morphologyThis section describes the attachment, the area and orientation of the superficial masseter muscle and its relationship with craniofacial morphology in dentate and edentulous subjects. A principal component analysis provided evidence that the lower masseter muscle width was associated with the size of ramus and was related to the position of the anterior margin of the muscle. The result of a linear discriminant function suggested that the ramus width, coronoid height and the distance between the anterior margin of masseter muscle and the mandibular notch contributed most to the observed difference between dentate and edentulous subjects. The results of this study indicated that a reduction of masticatory function was associated with the position of the anterior border of the insertion of the masseter muscle and also with differences in ramus dimension, the mos … More t significant of which were differences in the coronoid process and gonial angle.2. The relationship between bite force and craniofacial morphologyThe purposes of this section were to understand their specific jaw apparatus by comparing the dental arch morphology, craniofacial morphology and bite force and also to estimate the relationship between craniofacial morphology and bite in Fijians and Japanese. The measurements were taken on dental casts, cephalograms and dental prescale (bite force analysis ; occlusal area, average occlusal force and bite force). In every direction, the size of the dental arch in Fijians was larger than Japanese. And also Fijians had the large palatal length, mandibular length and mandibular body length and showed the bimaxillary protrusion. The inclination of the lower incisor in Fijians was more lingual than Japanese. There were significant differences in the lever armlength between Fijians and Japanese.3. The morpnhological characteristics of vertical sections of mandibles by CT scanningThe aims of this section were to compare the internal morphologies of vertical sections of the mandibular body and to evaluate the relationship between these morphologies and the gonial angle. As the result of the principal component analysis, each value of the sections was grouped into the same factor, except for the buccal cortical bone thickness. Especially the symphysis buccal cortical bone was opposite to the premolar buccal cortical bone. The gonial angle was associated with the buccal and lingual cortical bone thickness of the second molar section, and related to the height of the symphysis and the second molar section. These results confirmed the relationship between the gonial angle and the size of the mandibular body at the second molar region. This region was located near the ramus which had the attachment of masticatory muscles. Less