Objectives: The purpose of this study was to investigate the relationship between habitual masticatory side and dental arch. Methods: The subjects were 20 healthy dentulous persons from 22 to 23 years of age. The subjects' habitual masticatory side was evaluated as the principal component score in principal component analysis of asymmetric index (AI), calculated with 14 items of functional laterality. These items were selected for analysis: (1) Coefficient of variation was calculated from the cycle time during 10 strokes unilateral chewing of gum, (2) the number of strokes on each side during 30 free strokes chewing of gum, (3-5) occlusal contact force, (6-8) occlusal contact area and (9-11) electromyogram of the masseter, when the subject clenched for 3 seconds at maximum, 50% and 10% clenching force, and then a questionnaire about (12) habitual mastication side, (13) dominant hand and (14) dominant foot. Three-dimensional tooth positions were measured to analyze dental arch width by a three-dimensional measurement device on plaster molds of each subject. Measuring points on the study model were the center of the incisor edge , apex of the canine, premolar buccal cusp and molar buccal cusp, and then the perpendicular linear distances between the median line on HIP plane and the measuring points were calculated. Multiple stepwise regression analysis was performed as the explanatory variable on the 20 subjects' principal component score to evaluate habitual masticatory side, and the independent variable was the three-dimensional linear distance to show dental arch width. Results: From the results of multiple regression analysis, 5 independent variables were selected, bilateral premolar cusp and left second molar distal cusp, and partial regression coefficients of the left first premolar cusp and right second premolar cusp were significant (P<0.05). Conclusions: These results suggested that the habitual masticatory side correlated with dental arch width.

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