Regional Creep Response in the TMJ Disc

Research has focused primarily on the temporomandibular joint (TMJ) disc as a whole, overlooking regional differences. Objective: Examine and characterize viscoelastic property of creep for differences within and across regions of the TMJ disc. Methods: 14 TMJ discs, obtained from seven slaughterhouse pigs, were analyzed using an indentation testing technique on an ELF 3200 (Bose). Four discs were used to finalize testing protocol. Disc surfaces were divided into grids representing 9 regions (three anterior/posterior bands and three medial/lateral sections). Randomly ordered indentation tests were performed at each region on both the superior and inferior surfaces totaling 18 tests per disc. Each test consisted of a 50-gr compressive load sustained for 180 seconds with a 2-mm indentation tip. Data was collected at 1000-Hz. Tissue samples were soaked with physiologic saline throughout the experiment. Spring and dampening constants were obtained from E_R=1-(1-(τ_ε/τ_σ))e^-x where x=t/τ_σ. Paired t-tests and ANOVAs were used for data analyses. Results: Since testing surface (superior vs. inferior) and test order were not significant (p>0.05), subsequent analyses grouped regions. Differences in creep response were noted between anterior and intermediate bands at all time points (p<0.002), with the intermediate band demonstrating lesser response. Total creep response in the anterior band (42.1%±13.8%) varied compared with both the intermediate (26.0%±11.0%; p=0.001) and posterior bands (33.8%±12.6%; p=0.05). Only the posterior band showed medial/lateral differences with the central section undergoing less of a creep response than the lateral section during the final minute of the test (p<0.04). Spring and dampening constants for the intermediate band were different from other bands (p<0.02). Conclusion: Regional differences in creep response exist but are moderate. Overall, the intermediate band exhibited the smallest spring and dampening constants as well as the least change in strain response, indicating the greatest stiffness in these portions of the disc.