The region-dependent biphasic viscoelastic properties of human temporomandibular joint discs under confined compression.

The objective of this study was to determine the biphasic viscoelastic properties of human temporomandibular joint (TMJ) discs, correlate these properties with disc biochemical composition, and examine the relationship between these properties and disc dynamic behavior in confined compression. The equilibrium aggregate modulus (H(A)), hydraulic permeability (k), and dynamic modulus were examined between five disc regions. Biochemical assays were conducted to quantify the amount of water, collagen, and glycosaminoglycan (GAG) content in each region. The creep tests showed that the average equilibrium moduli of the intermediate, lateral, and medial regions were significantly higher than for the anterior and posterior regions (69.75+/-11.47kPa compared to 22.0+/-5.15kPa). Permeability showed the inverse trend with the largest values in the anterior and posterior regions (8.51+/-1.36x10(-15)m(4)/Ns compared with 3.75+/-0.72x10(-15)m(4)/Ns). Discs were 74.5% water by wet weight, 62% collagen, and 3.2% GAG by dry weight. Regional variations were only observed for water content which likely results in the regional variation in biphasic mechanical properties. The dynamic modulus of samples during confined compression is related to the aggregate modulus and hydraulic permeability of the tissue. The anterior and posterior regions displayed lower complex moduli over all frequencies (0.01-3Hz) with average moduli of 171.8-609.3kPa compared with 454.6-1613.0kPa for the 3 central regions. The region of the TMJ disc with higher aggregate modulus and lower permeability had higher dynamic modulus. Our results suggested that fluid pressurization plays a significant role in the load support of the TMJ disc under dynamic loading conditions.