Describe the two phases of mandibular movement during early mouth opening.

• A. Initial hinge rotation of the condyles, followed by translation (gliding) of the condyles and discs along the articular eminence
• B. Translation then rotation
• C. Hinge rotation only
• D. Translation only

Answer: (D)

During early mouth opening, the movement happens in two distinct phases. First, the condyles rotate like a hinge about the axis of the lower jaw joint, mainly in the inferior (lower) joint space. This hinge motion lets the mandible drop without significant forward glide. As opening progresses, the condyles and the interposed discs shift into a gliding phase, translating forward (and downward) along the slope of the articular eminence in the superior joint space. This translational, or gliding, movement allows a greater degree of opening and is driven by the coordinated action of the muscles, especially the lateral pterygoids, with the disc moving with the condyle. In short, you start with hinge rotation, then you move into translation along the eminence to achieve additional opening.