Application of digital image correlation to study the activity and functional heterogeneity of the human temporalis muscle in vivo during unilateral chewing: a preliminary study

Introduction: This study aimed to demonstrate the usefulness of digital image correlation (DIC) for analysing the activity and heterogeneity of the temporalis muscle based on its displacements. While the standard measure for superficial muscles traditionally relies on muscle force determined via electrical biopotentials and numerical simulations, this paper presents results indicating that a kinematic parameter (muscle displacement) can effectively assess muscle function. Methods: ). A Dantec Q400 non-contact measurement system based on DIC was utilised. Reference images were captured at the mandible's physiological resting position. The technique enabled continuous full-field mapping across the skin surface, while the final analysis was precisely confined to the area corresponding to the muscle fibres. Results and Discussion: The study demonstrated that the temporalis muscle's functioning is complex and structurally heterogeneous. Specifically, the analysis revealed two distinct kinematic patterns: an asymmetric cycle (AC) in the anterior and middle parts responsible for force generation, and a fluctuating cycle (FC) in the posterior part serving as a dynamic stabiliser for the temporomandibular joint (TMJ). Furthermore, muscle kinematics were significantly modulated by both the chewing side and food texture. Spatial activation patterns suggest a task-specific biomechanical strategy, where the working side presses the mandible, while the non-working side stabilises it against excessive rotation. Ultimately, the results confirm that skin surface displacement can serve as a reliable, high-resolution measure of temporalis muscle activity.