True Strain Characterization for Tmj Disc Tensile Testing

INTRODUCTION The temporomandibular joint (TMJ) is a bilateral synovial joint that is formed by the condyle of the mandible and the glenoid fossa of the temporal bone. In between these two bones is a fibrocartilagenous structure called the TMJ disc. Deterioration or displacement of the TMJ disc can lead to temporomandibular joint disorders (TMDs), which can cause symptoms such as pain, discomfort, joint dysfunction, and malocclusion. It is estimated that over 10 million Americans are affected by TMDs [1]. In addition, research estimates that 25% of the population will experience symptoms relating to TMDs at some point in their lives. [2]. Attempts to relieve pain associated with TMDs include medications, injection therapies, and/or surgical intervention. The current clinical treatment for patients with irreparable TMJ disc damage is to perform a discectomy. This can be done without graft replacements, which will lead to joint surfaces remodeling over time, or it can be done with autogenous tissue sources, which tend to resorb over time, making them ineffective for long-term treatment. Extracellular matrix (ECM) derived scaffolds have shown significant potential for local regeneration of damaged tissues in multiple biological applications. These scaffolds are derived from the matrix of natural tissues and are currently studied as an alternative to TMJ disc replacements. The ultimate goal is that these ECM scaffolds will remodel into a tissue that closely resembles the mechanical and biochemical properties of the TMJ disc. The hope is for these ECM scaffolds to become a long-term solution for TMDs and disc replacement therapies. Currently, our lab is investigating the use of ECM as a template for constructive remodeling in a porcine model. In order to determine the efficacy of the remodeled ECM, it must be characterized mechanically and compared to native discs. Current published tensile testing protocols, however, produce failure strain that is higher than those found in other cartilages. This suggests that the samples might be slipping during testing. For this reason, a novel method of assessing true strain needs to be established. Strain values are obtained by subjecting the native discs to elongation and forces, using a tensile testing machine. This testing apparatus records the maximum strain value immediately before the breaking point for the disc. We have developed a novel protocol for assessing true strain, in an attempt to determine if the samples are slipping and to also determine their true failure strain value.