Comparison of 3D surface and landmark-based analysis methods: The reliability and efficiency in determining asymmetry...

Our study sought answers on the reliability and sensitivity of landmark and 3D surface-based methods in detecting facial asymmetry.

Asymmetry analysis was performed using anatomical landmarks and surfaces from data obtained with a 3D scanner, and the amount of deviation was calculated according to the opposite half of the face. Resting, eyebrow-raising, eye closure, showing teeth, and whistling facial expressions were evaluated. The intraclass correlation coefficient (ICC) was used to calculate the method's reliability, and sensitivity in detecting asymmetry was tested by comparing healthy subjects and patients with the unpaired t-test. Seventeen patients and 20 healthy volunteers were analyzed.

Intraobserver and interobserver agreement of surface-based analysis ranged from high to excellent in healthy and facial paralysis individuals (ICC 0.77 to 0.99), while landmark-based analyses ranged from moderate to high agreement (ICC 0.60 to 0.91). Furthermore, for the sensitivity in detecting asymmetry, while the landmark-based system could detect statistically significant differences in 2 (eyebrow-raising and showing teeth) of 5 facial expressions (sensitivity = 0.4), the 3D system could detect differences in 5 of 5 (sensitivity = 1) (p < 0.05).

The 3D surface-based analysis method is more sensitive and reliable than the landmark-based method in determining facial asymmetry.