Biphasic Viscoelastic Properties of Human TMJ Disc

Objectives:  The temporomandibular joint (TMJ) disc serves to distribute joint loads, provide joint lubrication, and protect articular surfaces.  The TMJ disc is a viscoelastic material consisting of two principle phases: a solid matrix phase composed mainly of collagen and proteoglycan, and a predominant interstitial fluid phase.  This study determined biphasic viscoelastic properties of human TMJ disc.  The regional variation in mechanical properties was investigated.

Methods:  Twelve anatomically normal looking fresh TMJ discs were harvested from male cadavers.  Age at death ranged from 55 to 75 years.  Cylindrical samples (5mm diameter) with uniform thickness (~1.0mm) were prepared from the intermediate, posterior, anterior, lateral, and medial regions of the TMJ disc.  Each specimen was subjected to a 2-hour creep test, and followed by a dynamic test in a confined compression mode.  The equilibrium aggregate modulus and hydraulic permeability were obtained by curve-fitting creep data to the biphasic theory develop by Mow et al. (1980).  The dynamic complex modulus and phase angle were determined over the frequency ranging from 0.01 to 5 Hz.

Results:  The value of aggregate modulus of human TMJ disc is 59.3±25.5 kPa, which is much smaller than that of the human knee joint cartilage (15%).  The hydraulic permeability value is 9.7±0.36x10^-14m⁴/Ns, which is about two orders of magnitude higher than that of human knee joint cartilage.  The dynamic compressive modulus increases as the frequency increased, and the phase angle decreases as the frequency increased for all regions.

Conclusion:  The biomechanical properties of human TMJ disc are significantly different from those of cartilage present in other diarthrodial joints.  Significant differences in biomechanical properties exist in various region of the TMJ disc.  Our results suggest that pig might be a good animal model for TMJ disc biomechanics due to similar compressive mechanical properties.  (Supported by NIH P20RR-016461 and P20RR-017696).