Variation in human gape cycle kinematics and occlusal topography

ObjectivesThis study tested hypotheses relating intraspecific variation in occlusal morphology and intraspecific variation in jaw movements during feeding. Gape cycle kinematic variation was hypothesized to correlate with gape cycle number within a chewing sequence as well as with food toughness and stiffness. Gape cycle kinematic variation was also hypothesized to correlate with variation in occlusal area, slope, and volume. Methods and MaterialsTwenty-six adult human subjects chewed four foods with varying material properties while their jaw movements were recorded using three-dimensional coordinates of facial markers captured with a Vicon camera system. Post-canine occlusal morphology of each subject was quantified in ArcGIS using dental topographic analysis of dental casts. ResultsGape cycle duration did not vary with gape cycle number, food toughness, or food stiffness. Gape cycle vertical and lateral displacement correlated negatively with gape cycle number, while foods with higher toughness and Young's modulus had greater jaw vertical and lateral displacement. Subjects with steeper occlusal slopes had longer gape cycle durations and greater amounts of vertical displacement during the slow closing phase of the gape cycle. DiscussionThe results suggest that gape cycle durations are relatively consistent despite changes in food properties and gape cycle number, while occlusal slope affects gape cycle duration and vertical displacement during inferred occlusal contact. However, gape cycle number and bolus properties explain greater amounts of kinematic variation than does occlusal morphology.