Identification of Stable Anatomical Landmarks During Facial Expressions

Background: Identifying stable anatomical landmarks during facial expressions is necessary to register and align three-dimensional (3D) data, determine the common origin and motion axis, and calculate displacement, velocity, and acceleration of relative motion. Objective: Our study aimed to determine the stable anatomical landmarks during facial expressions. Methods: We included 30 volunteers in our study and asked them to perform resting, mouth opening, showing teeth, clenching teeth, eye closure, smiling, whistling, eyebrow raising, and disgusted facial expressions. We recorded the 3D movements of passive reflective markers with optoelectronic cameras, which we attached to 10 bilateral and 8 midline landmarks. Results: We determined that the inner corner of the eye while mouth opening, the hairline superior while showing teeth, the infraorbital rim while clenching teeth, the alare while eye closure, the inner corner of the eye while smiling, the mideyebrow while whistling, corners of the mouth while eyebrow raising, and hairline superior while disgust are the most stable anatomical landmarks. Conclusions: Our study identified immobile soft tissue landmarks specific to facial expression.