Three Dimensional Finite Element Research Of The Temporomandibular Joint With Anterior Disc Displacement

The temporomandibular joint is the only active joints of the cranial and maxillofacial. On anatomical morphology, the condylar articular surface of the unique shape, non-uniform thickness of the articular disc and complex muscle group around the articular fossa contribute to the stable and flexible ligament temporomandibular joints; On the physiological function, the temporomandibular joint functional movement, both rotating and sliding, participate in maxillofacial functions such as chewing, language and expression, which has always been considered to be an important weight-bearing joints and buffer structure. The temmporomandibular disorders, the most common of the temporomandibular joint disease with the morbidity of about20%, are clinically characterized by the pain of the joint main region, elastic ring, jaw movement anomaly and so on. The abnormal position and different deviation degree of the disc along the articular tubercle contribute to the temporomandibualr disorder which will aggravate clinical Clinical manifestations, even the serious complications such as disc perforation, condylar morphology change and movement disorders. There was lack of conclusion aimed at etiology,self-healing and outcome of it. The finite element analysis technology was used to analysis the mechanical distribution characteristics and laws of the anatomical structures and movement of the temporomandibular joint with anterior disc displacement on the intercuspal position(ICP) and opening position through the CT and MR imaging and3d reconstruction, which will contribute to the disease etiology and outcome of the temmporomandibular disorder with anterior disc displacement and guide diagnosis and treatment in clinical.Part I Reconstruction of the digital simulation model of the temporomandibular joint with anterior disc displacementObjectiveIn this study, we used CT and MRI scanning, combined with Free Form, Sinpleware and other reverse engineering software, to establish the digital simulation model of the temporomandibular joint with anterior disc displacement.Materials and Methods1、According to the diagnostic criteria for temporomandibular disorders, One volunteer with temporomandibular disorder was selected. X-ray and64-slice CT examination with the slice thickness0.5mm, ranging from the lower edge of mandibular to the base of skull was performed to exclude mandible diseases and tumors. The anterior disc displacement was diagnosed by oblique sagittal3-D MRI scanning which showed that the Drace was12.210and the plate boundary crossed the joint nodules.232clear CT bone window and MRI images was received and fromed to DICOM format.2、The digital simulation model of temporomandibular joint with anterior disc displacement was established by Simpleware and Ansys software on the basis of the imaging data obtained form the head spiral CT and3D-MR scanning.ResultsThe digital simulation models of temporomandibular joint with anterior disc displacement on intercuspal position(ICP) and opening position were successfully established, which accurately showed their anatomic structure such as disc, capsule, articular fossa, condylar cortical bone, cancellous bone and cartilage layer. The middle belt of the disc was not only rebuild accurately, but also objectively showed the attachment between articular disc, articular fossa and condylar.ConclusionsThe establishment of the digital simulation model of temporomandibular joint with anterior disc displacement consist of the disc, capsule, articular fossa, condylar cortical bone, cancellous bone and cartilage layer is high precise and verisimilar, which can be widely applied in the biomechanical research. PartⅡ Biomechanical analysis of the temporomandibular joint with anterior disc displacement on intercuspal positionObjectiveThis step is to simulate and biomechanical analysis of the temporomandibular joint with anterior disc displacement on intercuspal position by using the digital simulation model of the part I and to explain the biomechanics pathogenic mechanism law and functional influence of each anatomical structure on the temporomandibular joint.Materials and Methods1、The three dimensional finite element model of the temporomandibular joint with anterior disc displacement on intercuspal position was established by meshing of the Ansys.2、Bound borders and set up conditions:The lateral fossa surface closed to the temporal bone and skull base surface in X and Y axis were set as constraint; Using the masseter vector and attachment on the mandibular angle as the mechanical loading. The20pairs of masseter muscle bundle, simulated the masseter muscle fiber morphology, was loaded by200N following the masseter direction.3、Observation indexs:the stress distribution and movement of Structures consist of the disc, capsule, articular fossa, condylar cortical bone, cancellous bone and cartilage layer were observed on overall and three axails.Results1、The three dimensional finite element model of the temporomandibular joint with anterior disc displacement on intercuspal position was established. The model have geometric similarity, and vivid shape, generating97,983nodes and22,105units.2、On intercuspal position, the overall stress of cortical bone (x=0.78MPa) is similar to that of cancellous bone (x=0.77MPa), but is far more than the overall stress of the disc (x=0.38MPa) and cartilage layer (x=0.48MPa). The region of the highest stresses concentration was occurred in the functional region between the anterior slope of the condyle, articular fossa and disc; The maximum stress region of the disc was the lateral functional surface region, the contact between the boundary of middle and posterior belt of disc and condyle (x=1MPa) with the tendency of gradually reduce. In contrast to the inferior adherent region (x=0.37MPa), the most middle and post belt regions of the disc were on the low level (x=0.2MPa).3、There is an significant difference (t=-2.826, P=0.08) of stress distribution between the upper and lower surface on the anterior adherent of the condyle on the Y axis; The stress distribution difference occurred between the upper and lower surface on the functional region of the disc on the X axis (t=-3.142, P=0.014).4、The posterior-lateral functional and bilaminar region of the pseudo disc was the Overlapping regions of tear tape on the three axis.Conclusions1、Normal disc shift along with the anterior border region, which form a "pseudo disc" instead of normal structure and function of the normal disc. By reducing the height of the condyle, the functional region was enlarged to reduce pressure and adjust the pressure of attachment in order to restore position and function of joint.2、The posterior-lateral functional and bilaminar tear tape of the pseudo disc, the same to the disc perforation in clinic, will contribute to the reconstruction of the internal fiber, even the pathological changes such as breakage, reverse and so on. During the functional treatment of the anterior disc displacement, not only the release of the posterior belt and bilaminar region but also the relax of the anterior adherent of the condyle should be focused. Part III Biomechanical analysis of the temporomandibular joint with anterior disc displacement on intercuspal positionObjectiveThis step is to simulate and biomechanical analysis of the temporomandibular joint with anterior disc displacement on opening position by using the digital simulation model of the part I and to explain the biomechanics pathogenic mechanism law and functional influence of each anatomical structure on the temporomandibular joint.Materials and Methods1、The three dimensional finite element model of the temporomandibular joint with anterior disc displacement on opening position was established by meshing of the Ansys.2、Bound borders and set up conditions:The lateral fossa surface closed to the temporal bone and skull base surface in X and Y axis were set as constraint; Using the masseter vector and attachment on the mandibular angle as the mechanical loading. The20pairs of masseter muscle bundle, simulated the masseter muscle fiber morphology, was loaded by200N following the masseter direction.3、Observation indexs:the stress distribution and movement of Structures consist of the disc, capsule, articular fossa, condylar cortical bone, cancellous bone and cartilage layer were observed on overall and three axails.Results1、The three dimensional finite element model of the temporomandibular joint with anterior disc displacement on intercuspal position was established. The model have geometric similarity, and vivid shape, generating125,467nodes and35,741units.2、On opening position, the stress distribution varies from the different structures. The overall stress of cortical bone (x=2.8MPa) is similar to that of cancellous bone (x=0.79MPa), which are far more than the overall stress of the disc (x=0.38MPa) and cartilage layer (x=0.48MPa). The region of the highest stresses concentration was occurred in the contact region between the top and posterior region of the condyle and the posterior blet of disc with the tendency of gradually reduce.; The maximum stress region of the disc was the posterior region ast he whole posterior blet, the contact with the top and posterior region of the condyle (x=2.78MPa). In contrast to the anterior adherent region of the fossa (x=1.67MPa), the posterior belt and bilaminar region were on the low level (x=0.5MPa).3、There is an significant difference (t=5.905, P=0.004) of stress distribution between the upper and lower surface on the anterior attachment of the disc on the Y axis; The stress distribution difference occurred between the upper and lower surface on the laterl region of the disc on the X axis (t=2.782, P=0.005). So as the medial region(t=3.094, P=0.027)4、The laterl region of the anterior adherent of the fossa, the medial region of the posterior adherent of the foss, the posterior belt and the bilaminar region were the Overlapping regions of tear tape on the three axis.Conclusions 1、The main stress region of the condyle transform from the function region to the top and posterior region of the condyle. With the enlargement of the articular cavity, the reduction and surface change of the contact region results in the stress focused on the contact region between the top and posterior region of the condyle, the posterior belt and the articular tubercle.2、The adherent regions of the disc play a very important role in the stability and limit of the movement. The laterl region of the anterior adherent of the fossa, the medial region of the posterior adherent of the foss, the posterior belt and the bilaminar region are the main stree and function regions, resulting in the reconstruction of the internal fiber of the bilaminar region, even the pathological changes such as breakage, reverse and so on. During the treatment, the posterior belt and bilaminar region should be released. What’s more, the smooth movement process of the posterior belt through the top of the condyle should be considered as the key factor.