E3 Mechanical-Occlusal System

Topic

The masticatory system is a biomechanical mechanism composed of four elements functioning as a lever system: the mandible, acting as the system's bony lever; the masticatory muscles, acting as the actuators that move that bony lever; the temporomandibular joint, acting as the fulcrum and guide around which the bony lever pivots; and the teeth, acting as the contact points where the bony lever ultimately applies its force.

The mandible operates specifically as a third-class lever: the lever's fulcrum is located at the temporomandibular joint, and the muscular force applied by the masticatory muscles—primarily the masseter and temporalis—is exerted at a point between that fulcrum and the load (the dental contact where the biting force is ultimately applied).

The maximum biting force generated at the molars—the dental contact point furthest from the temporomandibular joint fulcrum—can reach between 800 and 1,200 newtons in an adult.

As a result of this lever-like arrangement, the temporomandibular joint, acting as the fulcrum, bears reaction forces that can exceed twice the biting force; the magnitude of these reaction forces depends on the position along the mandible where dental contact occurs: the closer the dental contact is to the temporomandibular joint fulcrum, the greater the reaction force the joint must withstand relative to the applied biting force.

In addition to generating biting force, the masticatory muscles—in coordination with the neuromuscular system—orchestrate the complete masticatory cycle: a three-dimensional mandibular movement combining mouth opening and closing with lateral movements (laterotrusion) and forward movements (protrusion). Within the temporomandibular joint, the contact pressure exerted by the mandibular condyle against the opposing articular surface is not distributed uniformly; instead, it concentrates according to the actual contact area between the two curved surfaces: the smaller the contact area for a given applied force, the greater the contact pressure concentrated on the mandibular condyle.

The temporomandibular ligament passively limits the extent of this masticatory cycle, acting as a mechanical constraint that prevents the mandible—as it moves within the temporomandibular joint—from exceeding its normal range of motion. Thus, the mandible, the masticatory muscles, the temporomandibular joint, and the teeth—initially identified as the four elements of the masticatory system—become coupled into a single lever mechanism; the temporomandibular ligament permits the movement of this mechanism, while the temporomandibular joint itself concentrates the forces involved during each masticatory cycle.

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