Effects of loading direction in prolonged clenching on stress distribution in the temporomandibular joint

Parafunctional habits, such as bruxism and prolonged clenching, have been associated with dysfunctional hy-peractivity of the masticatory muscles, including the lateral pterygoid muscle. The resultant loading to the temporomandibular joint (TMJ) is subject to the degradation of bone, cartilage and disc in the TMJ. In this study, we examined the effect of clenching direction on the stress distribution in the TMJ. In this line, we hypothesised that asymmetrical clenching involved in parafunction might result in increased stresses on the TMJ disc as well as on the condylar and temporal articular surfaces. The distribution of stress for various directional loadings was analysed using a three-dimensional finite element model of the TMJ, with viscoelastic properties for the disc. The numerical results revealed that load direction influenced the amount and distribution of stresses on the disc surfaces. In particular, the lateral region of the disc suffered higher stress values. Moreover, the results showed a significant stress relaxation in the disc that revealed its capacity for stress energy dissipation. From the present study, it can be established that during prolonged clenching, the higher stresses are concentrated in the lateral region, which could imply that TMJ disorders related to damage or wear in the disc and the condylar cartilage, overall, occur when lateral dysfunctional displacements are present.