The effect of head posture on facial soft tissue changes captured by white-light facial scanning

Objective: To investigate whether changes in head posture have significant effects on facial soft tissues during white-light scanning. Materials and methods: Thirty-four adult patients participated in the study in which 22 soft tissue landmarks were marked on the face of each subject using an oil-based pen. The subjects wore digital inclinometers on top of their heads, and sat relaxed with their heads orientated in natural head position (NHP), while a facial scan was captured. The subjects underwent a second facial scan in an upward 5 degrees(U5), upward 10 degrees(U10), downward 5 degrees(D5), or a downward 10 degrees(D10) direction with respect to the NHP. The NHP image was superimposed on the images taken at the different head postures and a single co-ordinate system was obtained. The axial reference plane (x-axis), the sagittal reference plane (y-axis) and the coronal plane (z-axis) were set with N' as the zero point (0, 0, 0). The changes in position of each landmark caused by the change of head posture were measured. Results: When the subject's head was in the U5 and D5 posture, changes in landmark identification were not statistically significantly different. When the subject's head was in the U10 posture, soft tissue Stmi and Li moved downward significantly. Soft tissue pogonion moved forward significantly in the D10 posture. Conclusions: Soft tissue changes within 5 degrees of the natural head posture were clinically negligible. If efforts to reproduce natural head position are carried out, reliable facial scanning images can be obtained without the support of any special head positioning tools.