Roles of the Fibrous Superficial Zone in the Mechanical Behavior of TMJ Condylar Cartilage

Abstract

In temporomandibular joints (TMJs), the cartilage on the condylar head displays a unique ultrastructure with a dense layer of type I collagen in the superficial zone, different from hyaline cartilage in other joints. This study aims to elucidate the roles of this fibrous zone in the mechanical behaviors, particularly lubrication, of TMJ under physiological loading regimes. Mechanical tests on porcine condylar cartilage demonstrated that the superficial and middle-deep zones exhibit tension-compression nonlinearity. The tensile and compressive moduli of the superficial zone are 30.73 ± 12.97 and 0.028 ± 0.016 MPa, respectively, while those for the middle-deep zone are 2.43 ± 1.75 and 0.14 ± 0.09 MPa. A nonlinear finite element model of condylar cartilage was built to simulate sliding of a spherical probe over the articular surface. The presence of the superficial zone significantly promoted interstitial fluid pressurization (IFP) inside the loaded cartilage and reduced the friction force on the surface, compared to the case without the superficial zone. Finite element simulations showed that IFP depends on sliding speed but not normal load, which matches the experimental results. This study revealed the presence of the fibrous zone can significantly reduce the deformation of condylar cartilage under compression and the friction force on its surface during sliding.

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Análise da estrutura e padrão de expressão de lubricina, SMAD2 fosforilada na cadeia de ligação e colágeno tipo I na cartilagem articular da mandíbula durante o envelhecimento

“…Sua incidência aumenta rapidamente após os 40 anos de idade 22 69 . Nas camadas mais profundas, mesmo ainda estando presentes feixes de fibras colágenas do tipo I, a resistência a tensão é bem menor.…”

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“…As altas densidades de cargas negativas, decorrentes dos grupos sulfato e carboxil dos carboidratos, atraem uma nuvem de cátions que são osmoticamente ativos, fazendo com que grande quantidade de água seja absorvida pela matriz (água de solvatação) criando uma pressão por turgor, que permite que a matriz suporte forças de compressão 74 . Na CA, a pressão de turgor é contrabalanceada pela rede de fibras colágenas 62,69 .…”