Mechanical characterization and viscoelastic model of the ovine temporomandibular joint Disc in indentation, uniaxial tension, and biaxial tension

There have been recent investigations into developing disc replacements and regenerative medicine to treat internal derangements of the temporomandibular joint (TMJ) disc. Previous attempts at disc replacements have faced challenges related in part to a limited understanding of the TMJ's complex mechanical environment. The purpose of this study was to characterize the mechanical behavior of the ovine TMJ disc and to derive viscoelastic constitutive models from the experimental data. Fresh ovine TMJ discs were tested in indentation stress-relaxation tests on the inferior surface, uniaxial tension tests to failure, and dynamic biaxial tensile tests. Results showed an order of magnitude stiffer behavior in tension in the anteroposterior (primary fiber) direction compared to the mediolateral direction. The stiffness in tension was much greater than in compression. Regional comparisons showed greater elastic moduli in indentation in the posterior and anterior bands compared to the central region. A hyper-viscoelastic constitutive model captured the dynamic stress-stretch behavior in both indentation and biaxial tension with good agreement. These data will support ongoing and future computational modeling of local TMJ mechanics, aid in biomaterials identification, and ultimately enhance development of implant designs for TMJ disc replacement.