Strain rate dependent orthotropic properties of pristine and impulsively loaded porcine temporomandibular joint disk

Abstract

The purpose of this study was to characterize the tensile stress-strain behavior of the porcine temporomandibular joint (TMJ) disk with respect to collagen orientation and strain rate dependency. The apparent elastic modulus, ultimate tensile strength, and strain at maximum stress were measured at three elongation rates (0.5, 50, and 500 mm/min) for dumbbell-shaped samples oriented along either anteroposterior or mediolateral axes of the disks. In order to study the effects of impact-induced fissuring on the mechanical behavior, the same properties were measured along each orientation at an elongation rate of 500 mm/min for disks subjected to impulsive loads of 0.5 N. s. The results suggested a strongly orthotropic nature to the healthy pristine disk. The values for the apparent modulus and ultimate strength were 10-fold higher along the anteroposterior axis (p < or = 0.01), which represented the primary orientation of the collagen fibers. Strain rate dependency was evident for loading along the anteroposterior axis but not along the mediolateral axis. No significant differences in any property were noted between pristine and impulsively loaded disks for either orientation (p > 0.05). The results demonstrated the importance of choosing an orthotropic model for the TMJ disk to conduct finite element modeling, to develop failure criteria, and to construct tissue-engineered replacements. Impact-induced fissuring requires further study to determine if the TMJ disk is orthotropic with respect to fatigue.

Evaluating Anisotropic Properties in the Porcine Temporomandibular Joint Disc Using Nanoindentation

“…[36][37][38]45,46 The disc continuously undertakes tensile, compressive, and shear mechanical loads from different directions during various functions, such as chewing and talking. 4,54 The articular disc of the TMJ is a fibrocartilagenous component that acts as a load absorber and makes the relative motion between the mandible and the surface of the temporal bone of the cranium possible. 11,[36][37][38][39][40]47 By distributing load and absorbing shock, the TMJ disc prevents stress concentrations between the articulating surfaces of the TMJ.…”

“…The collagen fibers are predominantly oriented in the anteroposterior direction with numerous branches in other directions. 4 The properties of the TMJ disc should be stiffer when indented in the direction of the collagen fibers; therefore, the disc should be stiffer in the anteroposterior direction. The results from nanoindentation tests correlate well with what is expected based upon the orientation of the collagen fibers.…”

“…2,14 Mechanical properties of the disc tissue can also be used in finite element models simulations 15 to understand the biomechanical response of the tissue under complex loading condition. There have been studies examining the shear, 32,49,52,53 compressive, 1,5,31,33 or tensile 4,13 properties of the TMJ disc. Most of these studies are done at the macroscale level, are destructive and require the tissue to be punched for gripping purposes, which can result in alteration of the collagen network structure.…”

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

“…Further, the importance of the pressure phase may have clinical relevance in that a normal TMJ disc would carry a significant portion of the applied load in vivo through the fluid phase, whereas a degenerated disc is likely to have properties that shift the load carrying to the solid phase, potentially contributing to mechanical fatigue. Hypotheses regarding changes to the tissue properties (e.g., fluid content, solid phase modulus and Poisson ration, and permeability 1,3,5,16,20,32,38,39 ) and their relation to disc function will be the subject of future studies.…”

“…As described shortly, the modulus values were determined to match indenter displacement, and the remaining constants were taken from the literature. 1,3,5,16,20,32,38,39 In future studies, these parameters will be adjusted automatically through optimization analysis coupled with biphasic finite element analysis.…”