Relation between 3-D morphology of dental arch and jaw function.

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PurposeThe purpose of this study is to clarify the characteristics of three-dimensional morphology of dental arch and jaw function in humans from infancy to adulthood, and how the relation between them develops.Subjects and MethodsThe subjects selected in this study were divided into five developmental groups : group K at kindergarten ; group E at elementary school ; stage J at junior high school ; group H at high school ; group U at university. Each stage included 8 subjects. Jaw movement at incisal teeth, jaw muscles' activities, relation between both of them, and the three-dimensional measurements of dental arch were analyzed.Results1. The shape of jaw movement was vertical line at group K and like a tear drop in other groups.2. Jaw closing muscles' activities were significantly larger in group K.3. Jaw closing muscles were activated before the start of jaw closing in group K and after in other groups, and those onsets were significantly longer in group U.Jaw opening muscle as activated before the start of jaw opening at all groups, and its onset was significantly longer in groups K and P.4. Larger longer diameter of dental arch and smaller width of alveolar bone in group K, and larger palatal inclination in groups K and P were significantly shown. The palatal depth increased with age.5. In the subjects with unilateral chewing habit, the upper and lower dental arches less overlapped.DiscussionJaw function in group K seemed to be underdeveloped. At stage P, developed jaw movement was shown like as in groups J, H and U, however, relations between jaw movement and muscles' activities seemed to be underdeveloped. Especially in the subjects with unilateral chewing habit, it was suggested that jaw function closely related to the morphology of dental arch.