A Biphasic Finite Element Model of In Vitro Plowing Tests of the Temporomandibular Joint Disc

Abstract

Disorders of the temporomandibular joint (TMJ) afflict 3-29% of people aged 19-40 years. Degenerative joint disease (DJD) of the TMJ generally occurs 15 years earlier than in other human joints and 1.5-2 times more often in women than men. The TMJ disc is the primary stress distribution mechanism within the joint. Mechanical failure of the TMJ disc precedes clinical signs of DJD. Unlike postcranial synovial joints, biomimetic replacements of the disc have not been successful, probably due to the paucity of knowledge about TMJ biomechanics. Translation of stress-fields mediolaterally across the TMJ disc may lead to fatigue failure because of the effect of traction forces on the tissue surface and because the disc is relatively weak in this aspect. Traction forces are composed of friction forces, which are known to be low in the TMJ, and plowing forces which are relatively much higher and result from movement and pressurization of fluids within the tissues due to translating surface loads. In the in vitro plowing experiment, a rigid curve-ended indenter is lowered into a TMJ disc that has been mounted on a stage with pressure gauges, and the indenter is then translated in a prescribed mediolateral motion that is intended to simulate the motion of the mandibular condyle on the TMJ disc in vivo. As a first step, these plowing experiments have quantified the variables thought to be important in tissue failure. A next step is to define the full role of these variables in the pathomechanics of TMJ disc tissue through a validated model. Therefore, the aim of this study was to develop and test a finite element model of the plowing experiments based on an orthotropic biphasic description of the soft tissue behavior of the TMJ disc. For this plowing model, the arbitrary Lagrange Eulerian method was used to approximate the moving load problem, where in vitro the indenter slid along the tissue's superior surface. Approximate validation of the plowing model was based on comparisons of model-predicted temporal and spatial distribution of indenter displacement and total normal stresses (+/-15%) and laboratory measurements during one complete cycle of plowing motion. Other useful predictions from the plowing model include spatial and temporal distributions of biomechanical variables of interest that cannot be measured experimentally, such as total stress, pressure, strain, and the relative significance of the orthotropic solid phase properties.

Biphasic Finite Element Modeling of Hydrated Soft Tissue Contact Using an Augmented Lagrangian Method

“…As with earlier biphasic implementations in COMSOL [18], solid mechanics in the Structural Mechanics Module and Darcy’s Law in the Earth Science Module were used and coupled to obtain the linear biphasic equations. The Contact Pair feature was used to enforce contact constraint for the solid phase and the Identity Pair feature was used to enforce fluid continuity constraint for the fluid phase.…”

An Augmented Lagrangian Method for Sliding Contact of Soft Tissue

“…In vitro experiments have been widely used to study the effect of sliding contact on biomechanical behavior of human diarthrodial joints [1–3]. However, not all of the mechanical components can be measured experimentally.…”

“…In order to analyze the contact mechanics in physiological joints, where geometry is far more complex, it is necessary to use numerical approximation methods such as the finite element method. Spilker et al [1, 2] used the arbitrary Lagrange Eulerian method along with a moving prescribed force to approximate the sliding contact problem and modeled plowing tests of the TMJ disc in 2D. Chen et al and Ateshian et al developed true sliding contact methods using a Lagrange multiplier method [4] and an augmented Lagrangian method [5], respectively.…”

Passive Strain-Induced Matrix Synthesis and Organization in Shape-Specific, Cartilaginous Neotissues

“…67,68 Similar strain levels have been predicted for both the meniscus and TMJ disc; FEA analysis has found tension-compression strain magnitudes in the range of ‡ 20-25% to correlate with normal physiologic loading. 69,70 Based on the present study's FEA analysis, it is predicted that the 10-g mass may be close to approaching an upper strain limit for passive axial compression, as maximum compressive strains in the ZZ-direction were found to be 21.8%. It is therefore important that future work determines whether higher passive axial loads are potentially more beneficial toward promoting enhanced functional properties in the biconcave neotissues and at which point the axial compression becomes detrimental.…”