Study on Masticatory System Development, by Observing Growth, Function and Eating Behavior as Indicators.

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It was attempted in this study to establish a quantitative developmental scale of masticatory system approaching from morphological, functional and behavioral aspects. In 1995, the previous studies were reviewed and several indices were selected to evaluate morphological, functional and behavioral development of the masticatory system in infanthood and childhood. There were few indices to scale eating behavior or ability for children. Thus, a standard scale for evaluating the progress of eating behavior, 'Eating food index' was established. In 1996, the crosssectional data was analyzed to consider characters of index and test correlation among indices. In 1997, morphological data (dental examination and measurement), functional data (EMG of masseter muscle activity, chewing efficiency, and bite force), behavioral data (eating food index and observing eating behavior) was analyzed longitudinally. Dental arch size became bigger, developmental space become prominent, amplitude of masseter muscle activity increased, chewing rhythm became stable, chewing efficiency, bite force and Eating food index increased with ages. These indices were related each other significantly. Developmental variable was composed from these indices by principal component analysis. During two years after birth, large variance within individuals were observed. Specially, during eighteen months after birth, functional indices were not reliable. However, it was suggested that this variable (developmental variable) in two or three years old could predict further development in five or six years old.