Stribeck Curve Analysis of Temporomandibular Joint Condylar Cartilage and Disc.

Temporomandibular joint (TMJ) diseases such as osteoarthritis and disc displacement have no permanent treatment options, but lubrication therapies, used in other joints, could be an effective alternative. However, the healthy TMJ contains fibrocartilage, not hyaline cartilage as is found in other joints. As such, the effect of lubrication therapies in the TMJ is unknown. Additionally, only a few studies have characterized the friction coefficient of the healthy TMJ. Like other cartilaginous tissues, the mandibular condyles and discs are subject to changes in friction coefficient due to fluid pressurization. In addition, the friction coefficients of the inferior joint space of the TMJ are affected by the sliding direction and anatomic location. However, these previous findings have not been able to identify how all three of these parameters (anatomic location, sliding direction, and fluid pressurization) influence changes in friction coefficient. This study used Stribeck curves to identify differences in the friction coefficients of mandibular condyles and discs based on anatomic location, sliding direction, and amount of fluid pressurization (friction mode). Friction coefficients were measured using a cartilage on glass tribometer. Both mandibular condyle and disc friction coefficients were well described by Stribeck curves (R2 range 0.87-0.97; p < 0.0001). These curves changed based on anatomic location (Δμ ∼ 0.05), but very few differences in friction coefficients were observed based on sliding direction. Mandibular condyles had similar boundary mode and elastoviscous mode friction coefficients to the TMJ disc (μmin ∼ 0.009 to 0.19) and both were lower than hyaline cartilage in other joints (e.g., knee, ankle, etc.). The observed differences here indicate that the surface characteristics of each anatomic region cause differences in friction coefficients.