Stress Analysis Of The Temporomandibular Joint During Mandibular Protrusive And Small Jaw Opening Movements With The Three-dimensional Finite Element Method

Temporomandibular joint(TMJ) is one of the most frequent usedjoints of the human. It is a geometrically complex and extremely flexiblecomposite joint with motion described by large translation and rotation.The growth, development and reconstruction of the TMJ and the factorsof temporomandibular diseases are all closely related to its mechanicalenvironment. Thus, many researchers pay more attention to thebiomechanics research of the TMJ gradually. The principal function ofthe oral cavity is chewing, swallowing, speaking and etc. And theimplementation of all these functions depends on mandibular movements.Mandibular movements have three basic functional movement styles, i. e.opening and closing movement, protraction and retropulsion movement,and lateral movement. And all these three basic movements cannot beaccomplished without the TMJ. The stress analysis of the TMJ duringmandibular functional movements can lead to better understanding of itsbiomechanics characteristics. Meanwhile, it can also provide a newmethod to explore the mechanism of the temporomandibular diseases andoffer the experimental basis of the treatment measures. Nowadays, the finite element method (FEM) has been the main means for biomechanicalstudy of the TMJ. There have been many reports about finite elementmodels of TMJ in recent years. They were mostly about the stressdistribution of the joint during clenching, but there was little researchabout the stress distribution of TMJ during mandibular movements. Nosatisfied solving measure has been found to load model to simulate themandibular movement. In this study, on the basis of images of theChinese Visible Human, the three-dimensional finite element model ofthe TMJ with occlusion was established. The boundary conditions,material properties and the contact relationships of the condyle, disc andfossa were defined in Patran. Then, displacement was introduced as theloading condition to simulate the mandibular protraction and small jawopening movement. Meanwhile, the stress distribution of the TMJ duringthe two movements was observed.Partâ… Stress analysis of the temporomandibular joint duringthe mandibular protraction by means of the three-dimensionalfinite element methodMaterials and Methods: On the basis of images of the Chinese VisibleHuman, the three-dimensional finite element model of the TMJ wasestablished, including dental arches, mandible, et al. Displacement wasintroduced as the loading condition to simulate the mandibular protraction from intercuspal position to edge-to-edge of dental occlusion.Then, the boundary conditions, material properties and the contactrelationships of the condyle, disc, fossa as well as upper and lower teethwere defined. The contact areas and stresses of various structures in theTMJ were calculated and analyzed in Marc.Results: The disc following the condyle moved downwards and forwardsduring protrusive movement. The anterior inclined plane of the condylecontacted with the center of the intermediate zone of the disc. Then thelateral inclined plane of condyle contacted with the lateral part of theintermediate zone of the disc while the top of the fossa contacted with theposterior band. The stress value of the lateral part of the intermediatezone of the disc (3.010Mpa) and the anterior inclined plane of condyle(5.500Mpa) were high. And on the same sagittal plane, the equivalentvon Mises stress of the condyle was the biggest, the ventral surface ofdisc was bigger than the dorsal surface and the fossa was the smallest.Conclusion: It was suggested that the concentrated areas of stress werein the lateral part of the intermediate zone of the disc and the anteriorinclined plane of condyle during protrusive movement; The intermediatezone of the disc was the important of stress buffer area. Materials and Methods: In Patran, rotation vector and user coordinatesystem were introduced as the loading condition to establish the jawopening model. Then, the boundary conditions, material properties andthe contact relationships of the condyle, disc and fossa were defined. Thecontact areas and stresses of various structures in the TMJ werecalculated and analyzed during small jaw opening in Marc.Results: During small opening, the condyle rotated upwards andforwards. At the same time, the disc slightly rotated upwards andforwards following the condyle. First, the posterior inclined plane of thecondyle contacted with the posterior border of the bilaminar region of thedisc, the medial and lateral part of disc contacted with the medial andlateral part of the condyle. While the anterior inclined plane of the fossacontacted with the posterior band. With the raising of the rotatedamplitude, the contact area of the condyle's posterior inclined plane andthe disc increases gradually, which from the bilaminar region to theposterior band. In the same sagittal plane, the equivalent von Mises stressof the ventral surface of disc was the biggest, the dorsal surface wasbigger than the condyle and the fossa was the smallest. While the openingextent enlarging, the von Mises stress of the joint increased.Conclusion: This model could precisely simulate the stress variation ofthe TMJ during the small opening movement; during the openingmovement, the disc, as a buffer area, more heavily loaded all the time because of the high incongruent of the joint surface's shape.