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

Abstract

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±11.47 kPa compared to 22.0±5.15 kPa). Permeability showed the inverse trend with the largest values in the anterior and posterior regions (8.51±1.36×10 −15 m 4 /N compared with 3.75±0.72×10 −15 m 4 /N). 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 (0.01-3 Hz) with average moduli of 171.8-609.3 kPa compared with 454.6-1613.0 kPa 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.

A Comparison of the Mechanical Properties of the Goat Temporomandibular Joint Disc to the Mandibular Condylar Cartilage in Unconfined Compression

“…Journal of Dental Biomechanics The collagen content of the goat TMJ disc is less than that of the previously reported porcine (68.2 ± 14.5%) and human TMJ disc (62.0 ± 11.4) [17,34]. We did validate our collagen assay with porcine samples and obtained results comparable to literature [35].…”

Effect of Mechanical Loading on Electrical Conductivity in Porcine TMJ Discs

“…The TMJ disc was considered as uncharged in this study, since biochemical studies have shown that the GAG content of human and porcine TMJ discs is very low (< 4% dry weight) compared with that of hyaline cartilage and IVD (Almarza et al, 2006;Kuo et al, 2010). For uncharged tissues in NaCl, the relative diffusivity (D/D 0 ) of NaCl is simply related to the relative conductivity by (Gu et al, 2004): where D is the mean ion diffusivity of Na + and Cl -in tissue, D 0 is the mean ion diffusivity in the bathing solution, χ is the electrical conductivity of the tissue, and χ 0 is the conductivity of the bathing solution.…”

Electrical Conductivity Method to Determine Sexual Dimorphisms in Human Temporomandibular Disc Fixed Charge Density

“…Based on the Donnan equation, electroneutrality condition and van’t Hoff’s equation for tissue osmotic swelling pressure 8 , cross-region FCD generates 11 kPa of osmotic pressure in males and 6.8 kPa of osmotic pressure in females. With the reported compressive modulus of the human TMJ disc in the range of 22–70 kPa with an average of 51 kPa 15 , osmotic pressure is approximately 20% of the overall compressive modulus of the TMJ disc. In comparison, the average FCD in healthy human knee articular cartilage (0.2 mEg/g wet tissue) can generate 155 kPa osmotic pressure, which has an average compressive modulus of 700 kPa 25 .…”