Viscoelastic Compressive Properties of Porcine TMJ Disc and Condyle Cartilage

Objectives:  The temporomandibular joint (TMJ) disc serves to decrease contact stresses and minimize wear on articular surfaces covered with fibrocartilage.  This study determined creep and dynamic compressive properties of porcine TMJ disc and condyle cartilage.  The regional variation in mechanical properties was investigated.  This study is important for understanding the interaction between disc and condyle cartilage during joint motion.

Methods:  Twelve porcine TMJs from young adult pigs (~85Kg) were used for this study.  Cylindrical samples (5mm diameter, ~1.2mm thickness) were prepared from the intermediate, posterior, anterior, lateral, and medial regions of the TMJ disc.  Cartilage plugs (5mm diameter) were excised from both anterior and posterior of each condyle head.  The deep zone of each plug was removed to ensure a uniform thickness.  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 modulus and phase angle were determined over the frequency ranging from 0.01 to 5 Hz.

Results:  The value of aggregate modulus of porcine TMJ disc (86.2 ± 30.7 kPa) is larger than that of condyle cartilage (19.6 ± 7.7 kPa).  The hydraulic permeability value of TMJ disc (6.17 ± 3.65x10^-14m⁴/Ns) is about four times smaller than that of condyle cartilage (24.1 ± 9.88x10^-14m⁴/Ns).  TMJ disc has higher dynamic compressive modulus and smaller phase angle.

Conclusion:  The compressive properties of TMJ disc are significantly different from those of condyle cartilage.  TMJ disc is much stiffer and less permeable than condyle cartilage.  Significant regional variations of compressive properties were found in both disc and condyle cartilage.  Our results provide new insights into load distribution and joint lubrication in TMJ. (Supported by NIH P20RR-016461 and P20RR-017696).