Application of 3D Models to Assess Natural Motion of Facial Muscles

The study presents a methodology for assessing the natural dynamics of facial soft tissues based on stereophotogrammetric 3D models, designed to differentiate physiological (natural) and pathological changes. In a 6-month study involving 6 subjects (20-25 years old), monthly synchronous facial survey was performed. We took pictures of the persons in two modes – static (neutral expression) and dynamic (8 facial expressions) using a 15-camera Canon EOS 550D (0.06 mm/pix resolution). Data processing included construction of triangulated 3D models at a density of 1 point/mm (RMSE = 1 mm), automatic detection of 468 key points via MediaPipe Face Mesh with asymmetry calculation, and profile analysis of orthophotos with Gaussian filtering. The results revealed an average variation of topography in the range of 0.55–0.7 mm for static models and peaks up to 5 mm for mimicry. The paper proposes a variant of automated angle measurement using orthophotos in full-face and profile, as well as a method for calculating the total angle of asymmetry as the average of the angles of eyebrows, eyes, nose and mouth.