Regional Stress Relaxation Characteristics in the Porcine Temporomandibular Joint Disc

Objective: Limited evidence exists demonstrating the temporomandibular joint (TMJ) is differentially loaded during in vivo function. This study's objective was to investigate regional variation of stress relaxation response in the TMJ disc.

Methods: Twelve TMJ discs were excised from six slaughterhouse porcine specimens. Four discs were designated to finalize testing protocols. All discs were divided into nine regions on both superior and inferior surfaces. Discs were tested by applying a 0.5mm compression strain to each region for 180s using an indention testing technique with a 2mm indentation tip (Elf 3200;Bose). Data was collected at 1000 Hz, and analyzed with ANOVAs and t-tests for regional differences of total stress relaxation response (TSRR) and viscoelastic time constants (VTC).

Results: No significant differences (p>0.05) between test order, surface, and side were noted for TSRR or VTC.

The anterior band TSRR (563.57+201.93g) was significantly different from the intermediate (291.44+174.46g: p=0.05) band at all time periods. No significant differences were noted between the medial, central and lateral slices (p>0.05), or between the nine individual regions (p>0.05).

The VTC were obtained by F(t) = K0 + K1 exp[(X1)t] + K2 exp[(X2)t]. Significant differences of K0 occurred between anterior (6.73+2.12) and intermediate bands (3.39+2.79: p=0.039) and of X2 between intermediate (-73.05+42.16) and posterior bands (-174.34+74.29: p=0.024). Significant regional differences of K0 occurred in posterior-lateral regions (9.59+4.99) compared to intermediate-lateral (2.40+3.11: p=0.035), and intermediate-central regions (2.56+3.10: p=0.042).

Conclusion: Regional variations of stress relaxation exist in the porcine TMJ disk. Since the intermediate band demonstrates the smallest viscoelastic response, this area, because of its stiffness, has the potential to absorb the greatest amount of compression.