Dynamic evaluation of facial muscles: 3D skin displacement vector analysis using a facial painting model

Abstract

Background: Botulinum toxin A can be used to eliminate dynamic wrinkles by relaxing the muscles involved in facial expressions. Therefore, it is essential to know the location, origin, insertion, function, and changes of the facial expression muscles according to their contraction. Methods: After drawing the muscles on the face of a model, pictures were taken at rest. The model was then asked to make facial expressions that cause facial wrinkles. All images were taken with the Vectra H1 camera system (Canfield Scientific, Inc., Fairfield, New Jersey). Each expression image was aligned to its respective static image to compute the differences in skin position, so as to calculate the skin displacement vectors. The values for local changes in skin displacement were calculated by applying the automated algorithms of the Vectra Software Mirror Suite and visualized using the color and size of the arrow. Results: Face painting and 3D skin vector displacement analyses enabled visualization of all the facial muscles involved in facial expressions working dynamically, allowing us to visualize the effect of each muscle in the creation of hyperkinetic wrinkles. Face painting and 3D skin vector displacement analyses can be combined to determine the location of the wrinkles, extent of the muscle, part of the muscle that contracts, presence of asymmetry, direction in which the muscle contracts, and correlation between the antagonists and synergistic muscles. Conclusion: The botulinum toxin A injection educational model using body painting and 3D skin vector displacement analyses can provide a deeper understanding of actual moving muscle anatomy. Level of Evidence: 4.