Experimental and coupled quasi-linear viscoelastic biphasic modeling of regional and strain-rate dependent tensile behavior in the temporomandibular joint disc

The temporomandibular joint (TMJ) is a load-bearing fibrocartilaginous articulation that sustains combined tension, compression, and shear. Although the TMJ disc exhibits strong regional and directional heterogeneity, its tensile properties and strain-rate dependence remain insufficiently characterized. Ovine TMJ discs were tested in the anterior, central, and posterior regions along the anteroposterior (AP) and mediolateral (ML) directions at strain rates of 0.1, 0.5, and 1%/s. Stress–strain curves were quantified, and the time-dependent response was modeled using a coupled quasi-linear viscoelastic (QLV) and biphasic framework. All specimens exhibited a nonlinear toe region followed by a linear tensile response. The AP direction showed substantially higher stiffness (up to 70 MPa), with the central region demonstrating the greatest modulus and ultimate tensile stress. Strain rate significantly influenced stiffness, with rate sensitivity more pronounced in the AP direction than in the ML direction (p < 0.05). The coupled QLV-biphasic model accurately reproduced the nonlinear elastic response (R² = 0.90–0.95). Fluid-phase parameters were adopted from the literature, while solid-phase parameters were identified by fitting to the experimental tensile data. These findings provide region- and direction-specific viscoelastic parameters to improve finite element modeling and support the design of mechanically appropriate disc replacements.