Functional movements of the mandible

Abstract

Starting from the closed position, a typical motion of the mandible can be summarized as follows: Both condyles begin the opening immediately downward and forward. Early in the closing stroke, the entire mandible moves laterally. The working side (lateral) condyle moves upward and rearward and reaches its terminal position at the most vertical rearward position of its path before the teeth approach each other far enough to intercuspate. This working side condyle appears to be nearly stationary in the sagittal view for the remaining part of the closing stroke, which is termed the Working Functional Movement (WFM). During the WFM, the working side condyle moves medially to its closed position, while the nonworking side condyle goes upward and laterally to its closed position. The food is usually on the same side as the working side condyle. The paths of motion of the condyles are quite similar for subjects with “normal” occlusions and malocclusions. The closed position repeatability is similar, ranging from 0.01 to 0.06 inch. This is in contrast to the paths of motion of the central incisor where differences among subjects with “normal” and malocclusion are easily detected. Of particular interest is the fact that for a higher percentage of chews, the central incisor remains motionless at closure for more subjects with “normal” occlusion than for subjects with malocclusions.