Three-dimensional motion analysis of facial movement during verbal and nonverbal expressions in healthy subjects

Functional impairments of facial expressions alter the quality of life and their quantitative analysis is key to describing and grading facial function and dysfunction. The aim of this investigation was to quantify 3D lip movements in a group of healthy young subjects. Lip movements during five repetitions of common and random sequences of vowels and nonverbal expressions were recorded using an optoelectronic 3D motion analyzer. The mean maximum displacement of facial landmarks was used to compute 3D unilateral mobility and the symmetry indices (SI) separately for each sex. Facial mobility was significantly greater during open-mouth than closed-mouth smiles. Facial movement among the subjects was largest during articulation of the vowel /a/and smallest for /i/. Lips were pursed with a SI very close to 95%, while smiles were slightly more asymmetric. The vowel /a/was articulated with significantly greater symmetry than /e/, /i/and /u/. The outcomes suggest that the proposed method characterized normal facial animations satisfactorily, so it could be a useful tool for assessing patients with facial lesions and dentofacial deformities. Patient assessment would profit from this quantitative approach, which would reduce discrepancies among several clinical examinations.