Fig. 1: The possible kinematics of mandible in a free, vertical jaw-closure.
In the left panel, the condylar axis serves as a fulcrum (FUL3) for a class 3 lever for the clockwise rotation of mandible (arrows). The anterior part of mandible moves upward. Minimal amount of reaction force is subjected to the temporomandibular joints, and the synovial spaces of the joints are presented as inflated circles. The middle panel depicts the instant of the first tooth contact of an AF-bite. The unyielding ANT-contact stops the original movement. The point of contact instantaneously creates a novel fulcrum (FUL2) for a class 2 lever, to causes an acute counterclockwise tilt of the body of mandible. The synovial fluid spaces of both jaw joints are presented to be deflated and flattened by the reaction force. The right panel illustrates an alternative course of the kinematics of mandible, where a BAT-contact occurs first (the BF-bite). The first contact in the left BAT-area instantaneously transforms into a fulcrum (FUL1) for a class 1 lever. The reaction force tilts the tip of mandible upward, whereas distraction of the ipsilateral joint (inflated circle), concomitant with compression of the contralateral joint (deflated circle), may be expected.
