Viscoelastic properties of the human temporomandibular joint disc in patients with internal derangement.

PURPOSE: This study investigated the viscoelastic properties of human temporomandibular joint (TMJ) discs in patients with severe internal derangement (ID). PATIENTS AND METHODS: TMJ discs obtained from 5 patients with severe TMJ internal derangement were analyzed. Normal discs derived from 2 fresh cadavers and 4 patients without ID served as the controls. The viscoelastic responses of the discs to tensile forces were evaluated by means of stress-strain analyses. RESULTS: The discs in both groups exhibited a nonlinear stress-strain relationship that was represented by a power function of the strain. However, after stress relaxation, the ID discs were likely to exhibit a linear stress-strain relationship. The instantaneous elastic moduli were almost the same in both discs, but the relaxed elastic modulus of the ID discs was significantly greater than that of the controls in lower strain range of less than 2%. CONCLUSIONS: ID discs are more rigid than normal discs. These findings suggest that the changes in viscoelastic property of the discs in patients with ID are somewhat different from those that occur with aging.