After 25 mm when the mouth is excessively open, which movement predominates?

After 25 mm when the mouth is excessively open, which movement predominates?

• A. Hinge/Rotational Movement
• B. Depression
• C. Translational Movement
• D. Elevation

Answer: (A)

The opening of the jaw happens in two phases. At first, the mandible mainly rotates around the condyles—like a hinge—so you get hinge/rotational movement. Once the mouth opens beyond about 25 mm, the jaw begins to slide forward along the articular eminences, with the condyle and disc translating anteriorly and slightly downward. This translational movement becomes the dominant pattern in the later stage of opening. So when the mouth is opened excessively beyond 25 mm, translational movement is the primary motion.

The opening of the jaw happens in two phases. At first, the mandible mainly rotates around the condyles—like a hinge—so you get hinge/rotational movement. Once the mouth opens beyond about 25 mm, the jaw begins to slide forward along the articular eminences, with the condyle and disc translating anteriorly and slightly downward. This translational movement becomes the dominant pattern in the later stage of opening. So when the mouth is opened excessively beyond 25 mm, translational movement is the primary motion.