American Board of Orthodontics (ABO) Practice Exam 2025 - Free Orthodontics Practice Questions and Study Guide

Question: 1 / 660

Which of the following best describes the nature of hinge motion in the TMJ?

Occurs in the upper compartment

Primarily involves lateral movement

Represent pure rotation

The correct description of hinge motion in the temporomandibular joint (TMJ) is that it primarily represents pure rotation. In the context of TMJ movements, first movements within the joint occur in the lower compartment where the condyle rotates around a fixed axis, resulting in this pure rotational motion. This occurs during the initial stages of opening the mouth, where the mandible pivots around the axes of the joint without any translational sliding of the condyle along the articular surface.

As the mouth opens wider, the motion transitions to a component of translation, but during the initial phase of mouth opening, hinge motion is characterized by this pure rotational movement. Understanding the mechanics of the TMJ is crucial as it highlights the intricacies of both normal and pathological movements of the jaw.

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Involves a combination of translation and rotation

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