Relationship between anteroposterior maxillomandibular morphology and masticatory jaw movement patterns

The causal relationships between oral function and craniomandibular morphol ogy are poorly understood. The aim of this study was to determine whether q uantifiable features of masticatory jaw movements and associated EMG activi ty correlated with variation in morphology as defined by the ANB angle. Thi rty-six healthy subjects with no previous orthodontic treatment, asymptomat ic masticatory muscles, and asymptomatic temporomandibular joints participa ted. While subjects chewed gum, jaw movement data and surface EMG data were digitized and then quantified into a 300 variable vector for each subject. ANB angle measurements were calculated from digitized tracings of lateral cephalographs. Step-wise linear regression and discriminant analyses were u sed to determine the relationship between the ANB angle and a subset of the variables defining jaw movement patterns and EMG patterns. A linear combin ation of seven jaw movements and EMG variables accounted for over 75% of th e variation in the ANB angle (adjusted R-2 = 0.78, P < .001). A jackknifed cross-validation of the discriminant analysis, which was forced to use the same seven variables as the regression analysis, resulted in correct classi fication of 14 of 20 skeletal Class I, 7 of 9 skeletal Class II, and 7 of 7 skeletal Class III subjects. These results suggest that there is an associ ation between anteroposterior skeletal morphology, as quantified by the ANB angle, and masticatory jaw movement patterns, as quantified in this study.