EMG-assisted forward dynamics simulation of subject-specific mandible musculoskeletal system.

Assessment of mandibular dynamics is essential for examining stomatognathic functions, and many kinds of stomatognathic diseases, such as temporomandibular joint (TMJ) disorder and jaw tumors, require individual diagnosis and rehabilitation treatments. Musculoskeletal models of the mandible system provide an efficient tool for fulfilling these tasks, but most existing models are generic, without direct correlation to subject-specific data. For this reason, the objective of this study was to establish a subject-specific mandible modeling framework based on clinical measurements, including medical imaging, jaw kinematics, and electromyographic (EMG) acquisition. First, a non-rigid iterative closest point method was performed to register muscle insertion sites. A flexible multibody approach was introduced to describe the large deformation behavior of jaw muscles. The EMG signals of the temporalis and masseter muscles were then utilized to determine their active forces. Meanwhile, a feedback loop for tracking desired mandibular kinematics was presented to calculate the activations of jaw opening and pterygoid muscles. The subject-specific muscle forces and TMJ joint loading during jaw opening-closing movements were then calculated based on forward-inverse coupling dynamics procedure. As a validation of the proposed framework, the mandible trajectories of seven healthy subjects were predicted and compared with experimental data. The results demonstrated unintentional movement of the head-neck complex together with the activation patterns of jaw opening and lateral pterygoid muscles for different people. The proposed framework combines musculoskeletal modeling with dental biomechanical testing, providing an efficient method of predicting and understanding the dynamics of subject-specific mandible systems.