Stress relaxation behaviors of articular cartilages in porcine temporomandibular joint.

In this study, we tested the compressive stress relaxation behaviors of the mandibular condylar and temporal cartilages in the porcine temporomandibular joint (TMJ). The aim was to determine the quantitative and qualitative similarities and differences of compressive stress relaxation behaviors between the two cartilages. Ten porcine TMJs were used; the articular surface was divided into 5 regions: anterior, central, posterior, lateral and medial. Compressive relaxation test was carried out at a strain level of 5% in each region of the two cartilages. The stress relaxation was monitored over a period of 5min. In all the regions of the two cartilages, the time-dependent stress relaxation curves showed a marked drop in stress within the initial 10s, which can be fitted by a standard linear viscoelastic model. The instantaneous moduli in the temporal cartilage were dominantly larger than those in the condylar cartilage, while the condylar cartilage had slightly larger relaxation moduli than the temporal cartilage except for the medial region. The both cartilages showed the regional differences in the compressive stress relaxation behavior, and in the temporal cartilage the lateral and medial regions revealed the largest values for the instantaneous and relaxation moduli. The present results demonstrate that the viscoelastic properties of compressive stress relaxation in both cartilages are region-specific, which might have an important implication for stress distribution and transmission along with the TMJ disc.

Dynamic compressive properties of articular cartilages in the porcine temporomandibular joint.

The mandibular condylar and temporal cartilages in the temporomandibular joint (TMJ) play an important role as a stress absorber during function. However, relatively little information is available on its viscoelastic properties in dynamic compression, particularly in a physiological range of frequencies. We hypothesized that these properties are region-specific and depend on loading frequency. To characterize the viscoelastic properties of both cartilages, we performed dynamic indentation tests over a wide range of loading frequencies. Nine porcine TMJs were used; the articular surface was divided into five regions: anterior; central; posterior; medial and lateral. Sinusoidal compressive strain was applied with an amplitude of 1.0% and a frequency range between 0.01 and 10 Hz. In both cartilages, the dynamic storage modulus increased with frequency, and the value was the highest in the lateral region. These values of E' in the temporal cartilage were smaller than those in the mandibular condylar cartilage in all five regions except the lateral region. The Loss tangent values were higher in the temporal cartilage (0.35-0.65) than in the mandibular condylar one (0.2-0.45), which means that the temporal cartilage presents higher viscosity. The present results suggest that the dynamic compressive moduli in both cartilages are region-specific and dependent on the loading frequency, which might have important implications for the transmission of load in the TMJ.