Development and biomechanical evaluation of subject-specific, anatomically complete 3D finite element models of the temporomandibular joint using the four-finger mouth-opening test.

BACKGROUND: Accurate biomechanical characterization of asymptomatic TMJ function requires anatomically complete, subject-specific models, yet such validated finite element (FE) frameworks remain limited.

OBJECTIVE: To introduce and technically evaluate a novel MRI-validated, kinematically -driven, anatomically complete, subject-specific 3D nonlinear FE TMJ framework, and to demonstrate its biomechanical responses in one asymptomatic subject and two Class II cases with mild and moderate anterior disc displacement during the four-finger mouth-opening test.

METHODS: Three subject-specific TMJ models were constructed using CBCT for hard tissues and high-resolution MRI for soft tissues. A hybrid anatomical workflow integrating 3D Slicer, Blender, and ANSYS SpaceClaim enabled complete maxillofacial reconstruction. Nonlinear FE simulations (ANSYS Workbench) quantified stresses in the disc, condylar head, condylar neck, articular eminence, and glenoid fossa using validated material properties, frictional contacts, and physiological kinematic loading derived from motion-capture trajectories.

RESULTS: MRI-based geometric and kinematic validation showed <5% error in disc rotational angle and condylar translation. In the asymptomatic subject, compressive stresses occurred in intermediate disc regions, with tensile stresses near anterior and posterior attachments. The mild displacement case showed elevated posterior disc and anterior condylar stresses, while the moderate case exhibited the highest disc, condylar head, and neck stresses 0.637 MPa and 1.40 MPa, respectively. Across all three individuals, maximum stresses occurred as the condyle advanced over the articular eminence.

CONCLUSION: This feasibility study introduces a validated, anatomically complete subject-specific FE TMJ model that captures rotation-translation in the asymptomatic case and restricted translation with elevated stresses in mild and moderate displacement, supporting future expansion.