Biomechanical response of mandibular condylar cartilage-on-bone to dynamic shear

Objectives: Shear stress can result in fatigue, damage and irreversible deformation of the mandibular condylar cartilage. However, as little information is available on its dynamic properties in shear they can not be related to habitual or incidental condylar loads. As generally cartilage behaves hyper-elastically, we tested the hypothesis that the dynamic shear properties of the condylar cartilage depend on the amount of shear strain. Methods: Ten porcine mandibular condyles were used for dynamic shear tests; two cartilage-on-bone plugs were dissected from each condyle. The specimens were clamped between the plates of a loading apparatus under a compressive strain of 10%. Dynamic shear was applied to the specimen by a sinusoidal strain of respectively 1.0%, 2.0%, and 3.0%. Results: The magnitudes of the dynamic shear moduli |G*|, G' and G” were found to be dependent on the frequency and the amplitude of shear loading. The dynamic shear moduli significantly increased with shear strain. Meanwhile, tand ranged from 0.2 to 0.4, which means that the cartilage is primarily elastic in nature and has a small but not negligible viscosity. Conclusion: The present results show that the behavior in shear of the mandibular condylar cartilage is dependent on the frequency and amplitude of the applied strain.