Sequentially coupled musculoskeletal multibody and finite element simulation for biomechanical modeling of the human masticatory system.

INTRODUCTION: Finite element (FE) models of the mandible are widely used for biomechanical analysis and preoperative planning in craniomaxillofacial surgery. However, their predictive reliability depends on a realistic representation of geometry, material properties, boundary conditions, and muscular loading, for which no clear consensus currently exists. Therefore, we developed a sequentially coupled computational framework that integrates boundary conditions from a validated inverse-dynamic, scaled-generic musculoskeletal multibody simulation (MMBS) of the human masticatory system under unilateral clenching into a subject-specific, quasi-static FE model of the mandible.

METHODS: The MMBS model was scaled to a mandibular geometry reconstructed from computed tomography (CT) images. Time-dependent muscle forces and mandibular landmark displacements were transformed from the MMBS to the FE coordinate system and implemented as loading and boundary conditions, respectively. Heterogeneous bone material properties were assigned from CT data. Additionally, a baseline FE model, using common literature assumptions, including static generic muscle forces, fixed boundary conditions, and homogeneous bone material properties, was defined. Starting from this baseline model, sensitivity analyses of the calculated strain and stress distributions in clinically relevant regions of interest were conducted to quantify the influence of bone material properties, applied muscle forces, and the muscle attachment area, thereby isolating the effect of each modeling advancement and demonstrating the value of the proposed MMBS-FE framework.

RESULTS: The sequentially coupled MMBS-FE framework predicted realistic mandibular biomechanics with the highest von Mises stresses and logarithmic strains occurring in the balancing-side condyle and the working-side molar region. Bone material properties were the dominant source of variation, causing changes of peak stress up to 161% and peak strain up to 723%, followed by more modest effects from applied muscle forces (up to 31%) and a negligible influence of muscle attachment area definition.

DISCUSSION: These findings highlight the critical importance of realistic modeling of heterogeneous bone material properties and personalized, time-dependent coordinated muscle forces that serve as loading in subject-specific mandibular FE models. This proposed MMBS-FE model serves as a proof-of-concept framework and offers recommendations for biomechanical modeling of the human masticatory system under unilateral clenching conditions. By incorporating these recommendations, researchers can improve pre-clinical evaluation of craniomaxillofacial implants and surgical strategies.