Biomechanical impact of sagittal curvature radius in glenoid fossa on TMJ prosthesis performance: A finite element study of custom designs.

Abstract

Statement of problem: Although custom temporomandibular joint (TMJ) prostheses manufactured via computer-aided design and manufacturing (CAD-CAM) and produced through 3-dimensional (3D) printing or computer numerical control (CNC) allow for sagittal curvature adjustments in the glenoid fossa, their design remains unregulated by the Food and Drug Administration. Consequently, the geometry is determined largely by the engineer's discretion, with limited biomechanical evidence to guide these decisions. The lack of validation regarding how sagittal curvature influences joint stress distribution under various anatomical and functional conditions represents a gap in current knowledge that warrants investigation.

Purpose: The purpose of this finite element method (FEM) study was to evaluate how variations in the sagittal radius of curvature of the glenoid fossa affect stress distribution in custom TMJ prostheses for 2 patients.

Material and methods: A 3D reconstruction of the temporomandibular joint of 2 patients was carried out. Temporomandibular prostheses were designed with different sagittal radii of curvature at the level of the rotary hinge depending on the occlusal plane, the customized orientation of the muscles, the angle of the occlusal plane and Frankfort plane, and the direction of the load at the level of the second left molar, using FEM. Subsequently, mechanical stresses and kinematic translation were evaluated based on boundary conditions, joint constraints, bone mechanical properties, and soft tissue properties.

Results: The semicircular base curvature radius #1 restricted the sagittal displacements of the prosthetic condylar head and increased the stress state on the articular surface. In contrast, the curvature radii #3 and #4 reduced the von Mises stresses and minimum principal stresses by 50% and optimized the translation of the prosthetic condylar component by 45%, respectively.

Conclusions: The findings suggest that incorporating elliptical sagittal curvature radii in the design of TMJ prostheses may offer biomechanical advantages over traditional spherical models. These geometries appear to facilitate more natural joint kinematics and reduce stress, supporting their use in personalized prosthetic development to enhance joint function, longevity, and patient outcomes.