What is the functional difference between the superior and inferior compartments of the temporomandibular joint?

What is the functional difference between the superior and inferior compartments of the temporomandibular joint?

• A. Lower compartment rotates (hinge); upper compartment glides (translation).
• B. Upper compartment glides (translation); lower compartment rotates (hinge).
• C. Upper compartment glides (translation); lower compartment rotates (hinge).
• D. Both compartments perform translation.

Answer: (C)

The joints in the jaw function with two spaces created by the articular disc, and each space moves differently to generate the overall mouth opening. In the lower compartment, the movement is hinge-like rotation of the condyle on the disc around a horizontal axis, giving a pure rotational opening at first. In the upper compartment, the condyle–disc unit slides forward under the articular eminence, producing gliding or translation rather than rotation as you open wider or protrude the jaw. This combination—rotation in the lower compartment and translation in the upper compartment—lets the mouth begin to open with a hinge motion and then extend the movement through forward gliding.

The joints in the jaw function with two spaces created by the articular disc, and each space moves differently to generate the overall mouth opening. In the lower compartment, the movement is hinge-like rotation of the condyle on the disc around a horizontal axis, giving a pure rotational opening at first. In the upper compartment, the condyle–disc unit slides forward under the articular eminence, producing gliding or translation rather than rotation as you open wider or protrude the jaw. This combination—rotation in the lower compartment and translation in the upper compartment—lets the mouth begin to open with a hinge motion and then extend the movement through forward gliding.