What is the expected change in the FMA angle in patients with vertical inocclusion?

What is the expected change in the FMA angle in patients with vertical inocclusion?

• A. increases
• B. decreases
• C. remains constant
• D. does not change

Answer: (A)

The main idea here is that FMA measures the angle between the Frankfort horizontal plane and the mandibular plane, which reflects how steep the lower jaw is relative to the cranial base. In vertical occlusion, the vertical dimension is increased and the mandible tends to rotate downward and backward to achieve contact, making the mandibular plane steeper. That rotation increases the angle between the mandibular plane and Frankfort horizontal, so the FMA rises. Therefore, the expected change is an increase in the FMA angle.

The main idea here is that FMA measures the angle between the Frankfort horizontal plane and the mandibular plane, which reflects how steep the lower jaw is relative to the cranial base. In vertical occlusion, the vertical dimension is increased and the mandible tends to rotate downward and backward to achieve contact, making the mandibular plane steeper. That rotation increases the angle between the mandibular plane and Frankfort horizontal, so the FMA rises. Therefore, the expected change is an increase in the FMA angle.