Effect of Hyperactivity of the Lateral Pterygoid Muscle on the Temporomandibular Joint Disk

Abstract

In this study, the effect of hyperactivity of the lateral pterygoid muscle (LPM) on the temporomandibular joint (TMJ) disk during prolonged clenching was examined with a mathematical model. Finite element models of the TMJ were constructed based on magnetic resonance images from two subjects with or without internal derangement of the TMJ. For each model, muscle forces were used as a loading condition for stress analysis for 10 min clenching. Furthermore, an intermittent increase of the LPM force with intervals of 1 min was applied. In the asymptomatic model, large stresses were found in the central and lateral part of the disk at the onset of clenching. In the retrodiscal tissue, stress relaxation occurred during the first 2 min of clenching. When the force of the LPM increased temporarily, the disk moved anteriorly and returned to its original position afterward. In the symptomatic model, large stresses were observed in both the posterior region of the disk and the retrodiscal tissue throughout clenching. Upon temporary increase of the LPM force, the disk was elongated anteriorly, which appeared to be irreversible. These results indicate that hyperactivity of the LPM may be involved in the progression of disk displacement.

Evaluating the correlation between the lateral pterygoid muscle attachment type and internal derangement of the temporomandibular joint with an emphasis on MR imaging findings

“…The inferior head of the LPM is active during jaw opening, jaw protrusion, and contralateral jaw movements and the superior head of the LPM during jaw closing, jaw retrusion, and ipsilateral jaw movements. Both heads have a reciprocal pattern of activity; however, intermingling of muscle bundles between the different heads has been observed anatomically (Tanaka et al, 2007;Fujita et al, 2001). It attaches to the capsule and the pterygoid fovea of the mandibular condyle, and may also insert directly into the disc (Bertilsson and Strom 1995;Naidoo, 1996).…”

Stress analysis in the mandibular condyle during prolonged clenching: A theoretical approach with the finite element method

“…Since the superior head of LPM attaches partly to the articular capsule of the TMJ and directly or indirectly to its articular disc [18,19], it has been hypothesized that dysfunction of this muscle can lead to degenerative changes [15,16]. Tanaka et al [20] recently investigated the effect of hyperactivity of LPM on the disc during prolonged clenching using a finite element (FE) model of the TMJ. The findings suggested that the hyperactivity of the LPM might be involved in the progression of abnormal anterior disc displacement.…”

Superior Head of the Lateral Pterygoid Muscle Inserting in Asymptomatic Temporomandibular Joints

“…To Tanaka et al (2007), LPM hyperactivity can cause progression of anterior disc displacement, while Taskaya-Yilmaz et al indicate that this disc condition causes morphological changes in the SHLP associated with lower muscular activity. The assumption that anterior disc displacement is caused by the overactivity of the SHLP has justified the development of therapies that aim to block the activity of the muscle fibers (Bakke et al, 2005); however, the existing literature offers insufficient evidence to support this hypothesis.…”