Changes in natural head position after orthognathic surgery in skeletal Class III patients

The purpose of this study was to evaluate the change in natural head position (NHP) after orthognathic surgery in skeletal Class III patients.

We used pretreatment (T1) and posttreatment (T2) cephalometric radiographs and T1 and T2 lateral facial photographs of 20 skeletal Class III patients (mean age, 21.6 years), with 20 skeletal Class I patients (mean age, 22.2 years) as the controls. The Class III patients had undergone mandibular setback surgery, and the patients in the control group had received conventional orthodontic treatment. All lateral facial photographs were recorded in NHP. The true vertical line (TVL) was transferred from the photograph to the cephalometric radiograph, and then the angle between the TVL and the Frankfort horizontal plane (TVL/FH) was measured. A t test and a paired t test were used to verify the differences between the 2 groups, and between the T1 and T2 measurements in each group.

The mean TVL/FH at T1 was significantly greater in the Class III group than in the Class I group; this indicated that the Class III group showed head flexion. However, the mean TVL/FH of the Class III group decreased by -3.1° at T2; this indicated head extension, and it did not significantly differ from that of the Class I group. Nineteen of the 20 Class I patients showed minimal or no change in their TVL/FH (-1.5° to 1.5°) at T2. On the other hand, 6 of the 20 Class III patients showed more than a 4.5° decrease in their TVL/FH at T2.

Most of the Class I patients showed minimal or no change in their NHP at T2, but some Class III patients had changes in their NHP that tended toward head extension after mandibular setback surgery. Thus, soft tissue analysis using the TVL in NHP may not be reliable for some skeletal Class III patients who undergo mandibular setback surgery.