Mechanical and micro-structural changes of inflamed temporomandibular joint disc

Degeneration of temporomandibular joint (TMJ) plays an important role in the Temporomandibular disorders. TMJ disc has great function in stress distribution during jaw movements and play important role in the progression of TMD. In our previous study, deformity, thickened, and changes of content of collagen and proteoglycan of the disc was found to be characteristic in the induced chronic inflammation of TMJ. This study was to evaluate the effect of chronic synovial inflammation on mechanical and micro-structural properties of TMJ disc.

Method: Chronic synovial inflammation was induced by double intra-articular injection of Complete Freund’s Adjuvant as previously described. The micro-structural and biomechanical (tensile and compressive) properties of the TMJ disc with or without inducing inflammation were examined by mechanical testing, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analysis.

Result: The instantaneous compressive modulus of inflamed anterior and posterior band was significantly decreased (P<0.01) in contrast to relevant bands of control discs. The instantaneous tensile modulus of inflamed discs showed significantly decrease both in the anterior-posterior direction and the mesial-distal direction (P<0.05). Relaxation modulus of inflamed discs presented the same tendency in both compressive and tensile tests in compared with the control group. The SEM analysis showed the surface of inflamed discs became rough and porous with the outer gel-like stratum of the three bands destroyed, resulting the plenty of collagen fibers exposed on the surface. The TEM analysis demonstrated the distribution of diameter of collagen fibers in the inflamed discs manifested in large range, and oversize collagen fibers (d>100nm) were increased.

Conclusion: Chronic inflammation resulted in derangement of collagen fibers, disruption of the surface morphology and decrease in the viscoelasticity of rat TMJ disc.