Viscoelastic Deformation of Mandibular Condyle Bone in Determining TMJ Osteoarthritis

Objectives: Temperomandibular joint (TMJ) osteoarthritis is characterized by degeneration of subchondral cortical and trabecular bone of mandibular condyle. When time-dependent viscoelastic daily loading including masticatory cyclic and occlusal constant loading surpass the adaptive capacity of TMJ condyle, severe degeneration of the TMJ can develop. The objective of this study was to assess the viscoelastic properties of TMJ condyle bone and examine if clinical cone beam computed tomography (CBCT) based bone density measures can estimate its viscoelastic behavior.

Methods:  Five pig mandibular condyles were obtained from 5 individual pigs (male, approx 6 months (~150lbs)). After removing soft tissue and cartilage, the top part of condyle was dissected by making a cut parallel to the occlusal plane starting at the middle of the mandibular notch. The specimens were scanned using CBCT at 200 micron resolutions. Bone mineral histogram was obtained by calibrating a CT attenuation value of each voxel to a mineral density using known phantoms. Dynamic mechanical analysis (DMA) of the condyle specimens was performed using a non-invasive compressive cyclic loading (-3±2N at 1 Hz) followed by a constant compressive creep loading (<-12N) and unloading cycles for 2 hrs.

Results:  Magnitude of cyclic energy dissipation (tan δ) was assessed 0.074±0.032. A substantial residual strain (925±408 με) was unrecovered after creep loading/unloading cycles. Coefficient of variation (COV) of bone mineral density had a strong positive correlation with creep rate (r=0.895, p<0.046).

Conclusions:  The tan δ of condyle was measured higher than the previously reported value (0.05) of other anatomic sites suggesting that the TMJ condyle has better ability to resist the cyclic loading than other bone. Development of residual strain indicates that prolonged creep can lead to progressive deformation of condyle. This creep propagation is likely controlled by the COV that accounts for degree of bone remodeling in condyle.