Validity of measurements for cycle-by-cycle variability of jaw movements: variability of chewing cycles in cases of prognathism

Abstract

Objective assessments of masticatory jaw movements for patients with a high degree of occlusal abnormalities are critical to elucidate the relationship between occlusal function and morphology. This study aimed to test the reliability and validity of measuring specific cycle-by-cycle variability of chewing jaw movements of patients with mandibular prognathism. The lower incisor-point movements were monitored using a 3D tracking device. Analyses consist of evaluations for the planarity of each cycle, cycle-by-cycle variances in orientations of the best-fit planes and instantaneous curvature of the trajectories. These spatio-temporal variabilities of chewing cycles for 12 adult females with good occlusion were compared with those for 12 female adult patients with mandibular prognathism. Five of the control subjects performed chewing on two separate occasions. Measurement outcomes were repeatable within each subject. For both groups, each single chewing cycle was characterized as reasonably planar. Orientations of the best-fit planes and curvatures of the trajectories during closing were more variable for patients than those for the control subjects. These findings suggest certain effectiveness of the present measurements of orientations of the best-fit planes and movement curvatures for scaling the variable nature of patients' masticatory jaw movements.