Effects Of The Treatment Of Occlusal Pad On Stress Distribution Of The Temporomandibular Joint In Temporomandibular Disorders Patients With Deep Overbite:Finite Elemet Analysis

BackgroundTemporomandibular joint disorders (TMDs) are common in adults. It is very complex for the cause of temporomandibular joint disorders. Malocclusion is a very important cause of temporomandibular joint disorders. There are many of abnormal occlusal factors, such as deep overbite, overgrowth of third molars、reversed overbite of posterior teeth、occlusal interference, etc. Deep overbite can affect the masticatory movement and EMG activity of the temporomandibular joint. Deep overbite is closely related with the cause of temporomandibular joint disorders. It is reported that the prevalence of temporomandibular joint disorders is13.2times for the patients with deep overbite than the normal.There are many treatments for temporomandibular joint disorders, such as various medications, various physical therapy, interocclusal therapy including various occlusal pad. Reversible method of treatment is the preferred treatment principles for temporomandibular joint disorders. We can make the interocclusal therapy with various occlusal pad.Nowadays, FEM (Finite Element Method) has been widespreadly applied in medicine with communication between the various disciplines. Finite Element Method is a research method in mechanics at the beginning of the study. Finite element analysis is applied to the medical field by Friedenberg for the first time in1969. Four years later, two-dimensional finite element analysis method is applied to the field of oral medicine by Thresher and Farah. At present the finite element analysis method is applied to various fields of oral medicine. Three dimensional finite element stress analysis method are used extensively for tooth, periodontal ligament, alveolar bone, post-and-core crown, removable partial dentures, fixed partial denture, implant denture, complete denture and temporomandibular joint. However, we have not yet seen the reports that the three-dimensional finite element stress analysis for the temporomandibular joint disorders patients before and after the treatment of occlusal pad. The patient is temporomandibular joint disorder with deep overbite.ObjectiveThe purpose of the study was to in-depth study of deep overbite patients with temporomandibular joint disorder and know clear the biomechanical relationship among TMJ condyle, glenoid fossa, articular disc and the mandible. In this study we establish the three-dimensional finite element model of the temporomandibular joint and mandible for the deep overbite patient with temporomandibular joint disorders. Occlusal force is applied before and after the treatment of occlusal pad, Then we analyze the stress distribution in the temporomandibular joint and mandible case. Biomechanical relationships we can better depth study of deep overbite patients with temporomandibular joint disorder TMJ condyle, glenoid fossa and articular disc and between the mandible.Materials and methods1Setup and process of the three-dimensional Computer Aided Desiqn model for the mandible and temporomandibular joint.1.1Model ing materialWe chose a24-year-old temporomandibular joint disorder patient with deep overbite as a volunteer. We make the treatment of occlusal pad for the patient’s temporomandibular joint disorder. Dual-source computed tomography scans were performed before and after the treatment of occlusal pad, then we obtain image data of the temporomandibular joint area.1.2Dual-source computed tomography scanComputedtomography scan from the top of of the skull to the lower edge of the mandible. We selectively reconstruct thin layer of image as needed. Scanning parameters were the slice thickness0.6mm, reconstruction interval0.3mm, window width1500, window level450, tube voltage of120kv. Scanned images stored in DICOM format data which obtained after the scan is completed.1.3Image processing The above documents were conducting input software Mimics. The target area boundaries will be extracted by using the segmentation tool. So we have completed the establishment of the geometric model.1.4The extraction of the Computer Aided Desiqn model for the articular disc of the temporomandibuIar joint.With the software Magicsl2.0, we select the location of the articular disc matches the region from mandibular condyle articular surface, generating an articular disc about2.0mm thickness. Then Boolean operations between the articular disc and the mandibular model, and we can get the Computer Aided Desiqn model for the articular disc of the temporomandibular joint.2Establish and handling of the three-dimensional Finite Element model for the mandible and temporomandibular joint.2.1The generation of the three-dimensional finite element modelRead the geometric model builted above steps with the using of CAD interfaces from the Mentat of the software MSC. Marc2005. Complete the establishment of a three-dimensional finite element model after the meshing.2.2Assuming analytical conditionsMaterials and organizational of the model is assumed to be continuous, homogeneous, isotropic linear elastic material. As the human skeleton is a living material anisotropy and has much elastic constant anisotropy, Therefore it is generally be simplified as orthotropic. Because the bones have weak anisotropy, it can also be further simplified as isotropic. Material deformation is small deformation force. 3Operation of the three-dimensional finite element modelLoad is applied to the selected tooth. Measure the area of the contact parts by the use of software. Surface pressrure converted is applied. Each tooth loading force values reference the determined experimentally by Jing-jie Wang etc. The use of the area calculation function of the MSC. MARC, The loading force is converted to compressive stress in the surface. The six loading conditions were anterocclusion, centric biting pressure and the unilateral molar occlusal before and after treatment.4AnalysisMeasure the maximum and minimum Von Mises stress and deformation in various parts of the temporomandibular joint before and after the treatment of occlusal pad. Observe and analyze the trends of the stress and displacement. As most scholars believe that under normal circumstances, both sides of the TMJ and its Von Mises stress distribution is symmetric, therefore the study only observed the changes of the Von Mises stress of unilateral TMJ.Results1Completed the establishment of the three-dimensional finite element model of living tissue by dual-source CT scanner combined with Mimics software, Magics software and finite element analysis software MSC. Marc.In this study, we have successfully established the three-dimensional finite element model of the mandible and temporomandibular joint before and after the treatment of occlusal pad for the deep overbite patient with temporomandibular joint disorder.2Access to the data of the finite element stress analysis such as Von Mises stress and displacement deformation cloud for the various parts of TMJ by the six loading conditions including anterocclusion, centric biting pressure and the unilateral molar occlusal before and after treatment.3Analysis of the stress variationThe stress distribution trends in various parts is roughly the same, the stress contours is similar, but different size of the force under different loading conditions. The size of the stress for the model contact area:the unilateral molar occlusal) centric biting pressure) anterocclusion. The stress of each model after the treatment of occlusal pad is less than the stress before the treatment of occlusal pad under the same loading condition. The order of the stress in various parts is as follows:condylar neck> the top of the condyle>the articular surface of the temporal bone> articular disc ventraDthe back area. Stress after the treatment of occlusal pad compared with before the treatment of occlusal pad reduced15-40%. After the treatment with occlusal pad, the stress distribution of the TMJ and the mandible for the deep overbite patient with TMD is more reasonable than before treatment.2Analysis of the displacement variation.Deformation and displacement of all the finite element model: the unilateral molar occlusal) centric biting pressure) anterocclusion. Deformation and displacement decreases after the treatment of occlusal pad. The displacement of the condylar is the largest, and the second is the articular disc, the glenoid fossa is the smallest during the TMJ area. Conclusions1It is a fast, accurate method for the establishing the dimensional finite element model of the temporomandibular joint and the mandible with the dual-source CT scanner, Mimics software, Magics software and software MSC. Marc. The method should be widely applied.2It is effective for the use of the occlusal pad to the deep overbite temporomandibular joint disorder patients.3The stress of each model after the treatment of occlusal pad is less than the stress before the treatment of occlusal pad under the same loading condition. After the treatment with occlusal pad, the stress distribution of the TMJ and the mandible for the deep overbite patient with TMD is more reasonable than before treatment.