Fig. 4.  The mean deviation of the Frankfort plane angle (A ) and the mandible plane angle (B ) from neutral position (0 cm head elevation) in the fixed-jaw and free-jaw groups. *P < 0.05 versus  neutral position (0 cm head elevation). The condition main effect (# P < 0.05 fixed-jaw vs.  free-jaw). Diagram of head elevation associated with increase in Frankfort plane angle and mandible plane angle from neutral position (0 cm head elevation) (C ).