Tensile stress patterns predicted in the articular disc of the human temporomandibular joint

Abstract

The direction of the first principal stress in the articular disc of the temporomandibular joint was predicted with a biomechanical model of the human masticatory system. The results were compared with the orientation of its collagen fibers. Furthermore, the effect of an active pull of the superior lateral pterygoid muscle, which is directly attached to the articular disc, was studied. It was hypothesized that the markedly antero-posterior direction of the collagen fibers would be reflected in the direction of the tensile stresses in the disc and that active pull of the superior lateral pterygoid muscle would augment these tensions. It was found that the tensile patterns were extremely dependent on the stage of movement and on the mandibular position. They differed between the superior and inferior layers of the disc. The hypothesis could only be confirmed for the anterior and middle portions of the disc. The predicted tensile principal stresses in the posterior part of the disc alternated between antero-posterior and medio-lateral directions.

Fig. 2

Direction and magnitude of the first principal stress in the TMJ disc during an open–close–open cycle in a superior view. The disc is made transparent. Upper row: Stress in the superior layer, lower row: stress in the inferior layer. a, anterior; p, posterior; m, medial; l, lateral.

Fig. 1

Principal stress in the TMJ disc in a sagittal cross-section during an open–close–open cycle. Upper row: first principal stress in the upper and lower layer of the disc as situated relative to the temporal and condylar cartilage layers. Arrows: direction of first principal stress. Green – blue: tensile stress, yellow – red: compressive stress. The cartilaginous structures are made transparent. Lower row: concomitant position of the mandible with respect to the skull.

Fig. 3

Direction and magnitude of the first principal stress in the TMJ disc during an open–close–open cycle after detachment of the superior lateral pterygoid in a superior view. Upper row: Stress in the superior layer, lower row: stress in the inferior layer. a, anterior; p, posterior; m, medial; l, lateral.

Fig. 4

First principal stress in the TMJ disc during a loaded open–close–open cycle. (A) Superior lateral pterygoid is attached to the articular capsule and disc. (B) Superior lateral pterygoid detached from the articular capsule and disc. Orientations and legends as in Figs 2 and 3.