Effect of jaw opening on the stress pattern in a normal human articular disc: finite element analysis based on MRI images.

Introduction: Excessive compressive and shear stresses are likely related to condylar resorption and disc perforation. Few studies have reported the disc displacement and deformation during jaw opening. The aim of this study was to analyze stress distribution in a normal articular disc during the jaw opening movement.

Methods: Bilateral MRI images were obtained from the temporomandibular joint of a healthy subject for the jaw opening displacement from 6 to 24 mm with 1 mm increments. The disc contour for the jaw opening at 6 mm was defined as the reference state, and was used to establish a two dimensional finite element model of the disc. The contours of the disc at other degrees of jaw opening were used as the displacement loading. Hyperelastic material models were applied to the anterior, intermediate and posterior parts of the disc. Stress and strain trajectories were calculated to characterize the stress/strain patterns in the disc.

Results: Both the maximum and minimum principal stresses were negative in the intermediate zone, therefore, the intermediate zone withstood mainly compressive stress. On the contrary, the maximum and minimum principal stresses were most positive in the anterior and posterior zones, which meant that the anterior and posterior bands suffered higher tensile stresses. The different patterns of stress trajectories between the intermediate zone and the anterior and posterior bands might be attributed to the effect of fiber orientation. The compression of the intermediate zone and stretching of the anterior and posterior bands caused high shear deformation in the transition region, especially at the disc surfaces.

Conclusions: The stress and strain remained at a reasonable level during jaw opening, indicating that the disc experiences no injury during functional opening movements in a healthy temporomandibular joint.