A Three-Dimensional Finite Element Study Of The TMJ With Different Spee Curve

The TMJs are load-bearing joints remodeling all the life.The load on the TMJs has been proven to play an important role in TMJ's structure and function as well as the etiology and therapy of TMD.Occlual force is the most direct origin of the load. Occlusion,TMJ and masticatory muscles are the major components of the interconnected biomechanical systems,the masticatory system.They are obviously interdependent because a change in any part will clearly affects the other two parts.The consonance of change in occlusion and the remodeling ability of the TMJ is the important precondition of their coordination. If the coordination is broken down ,TMD may occur.The curve of Spee (CS) is an important character of the mandibular dental arch. The curvature of Spee curve was significantly related to the horizontal position of the condyle with respect to the dentition.Clinical data also show that the change of Spee curve has something to do with the stress distribution in the TMJ.With the broad use of finite element method in stress analysis in stomatology,many native and foriegn scholars put up studies on three-dimension stress distributions of the TMJ with different kinds of Occlusion.But there is no report of finite element analysis of the stress distributions in TMJ with different Spee curve.The current study analyzed the stress distribution in TMJ with different Spee curve by FEM.The geometry of the model was based on the Thin-layer CT images of a volunteer with highly selected sound dentitions and asymptomatic joints.Then CT scan was served by DICOM. Mimics 3D reconstruction software was employed to process the data and to calculate the 3D model. Then this model was imported into the Abaqus software for being meshed and analyzed.Utilization of the thin-layer CT scanning made the model more precise. Utilization of Mimics software made the reconstruction of model more rapid. We designed 4 kinds of model based on clinic.Model 0: the curvature of CS was 2.50mm, the vertex was at the cuspis of the second premolar. Model 1: the curvature c of CS was 0 .Model 2: the curvature was 4.50mm,the vertex was at the cuspis of the second premolar.Model 3:the second premolar and the first molar on the right were lost,while the curvature was 2.50mm. Applied each model with vertical load.Results:â‘ Thin-layer CT technology and finite element method were organically combined.According to the correlation of gray-scale,density and elastic modulus, as well as the empirical formula, the mandible was assigned to multiple materials, which reflects the characteristics of non-uniform materials of mandible and is closer to reality about the last results.â‘¡The stress distribution patterns of TMJ with different curve of Spee is similar to that of normal occlusion.The Mises on the anterior surface of condyle is higher than that of ridges,posterior surface of condyle.While the Mises of lateral region is higher than that of medial region. The Mises of the posterior surface of condyle is well-distributed.The S,Max.Principal of the condyle is mainly tensile, The S,Min.Principal of the condyle is mainly compressive, the crest value lays in anterior surface. The the crest value Mises of the disc lays in ventral aspect of intermedial zone, higher than that of back of the disc.The Mises of the anterior band and posterior band are low, be well-distributed. The S,Max.Principal of the disc is mainly tensile, The S,Min.Principal of the disc is mainly compressive, the crest value lays in the intermedial zone. The final results also validate the anterior surface of condyle and intermediate zone of articular disc are the weight-bearing areas in TMJ.â‘¢The change of Spee curvature has effect on the the stress distribution when there is no tooth loss.When the Spee curve's curvature is 0, the the stress of anterior surface of condyle and intermediate zone of articular disc have a tiny addition compared with the original value.When Spee curve's curvature is 4.50mm, the stress of anterior surface of condyle and intermediate zone of articular disc has subtraction compared with the original value. The Mises of condyle and intermediate zone of articular disc increases obviously when unilateral posterior teeth are lost. Deviation is 0.036Mpa and 0.017Mpa.Conclusion :â‘ With the same plane of occlusion , the stress distribution patterns of TMJ with different curve of Spee is similar to that of normal occlusion.The anterior surface of condyle and intermediate zone of articular disc are the weight-bearing areas in the temporomandibular joint.â‘¡The changes of Spee curve change the value of the stress.â‘¢The value of the stress is inversely proportional to the change of Spee curve when there is no teeth lost. Unilateral posterior teeth loss increases the loading of TMJ.