Image Fusion And Finite Element Modeling Study Of The Temporomandibular Joint

Temporomandibular Joint (TMJ), as the most delicate and complicated joint ofhuman body, is composed of two joints, which, combined with several jaw muscles,make it possible to open and close the mouth. They work together when a person chews,speaks and swallows. Since the TMJ is the most frequently used joint of all the bodyjoints, it has high incidence of temporomandibular joint disoder (TMD), and also highlyexposable and vulnerable to trauma. Therefore the research of TMJ has highly clinicalsignificance. Due to the complexity of its anatomical structures, traditional researchmethods were always time-consuming, expensive and non-repeatable. With theapplication of mathematics and computer science in this field, more effective methods ofanalyzing the biomechanical behaviour of TMJ has been invented, in which of themfinite element method is the typical representative. With the quick development ofmedical imaging and finite element method, it is an inexorable trend to combine realisticconstitutive models, geometries and loads in order to predict the biomechanical responseof the different components of the joint both for symmetric and nonsymmetricmovements. In this paper, A three dimensional finite element model of the TMJcomprising the bone components, both articular discs, and the temporomandibularligaments was developed, by using SCT and MRI scanning,3D reconstruction, imagefusion, and finite element method. A lateral excursion of the mandible and clenchingwere introduced and the biomechanical behaviour of both TMJ sides was studied. Afibre-reinforced porohyperelastic model was introduced to simulate the behaviour of thearticular discs, taking into account the orientation of the fibres in each zone of thesecartilage components. The mandible movement during its lateral excursion wasintroduced as the loading condition in the analysis. The specific generated TMJ model’sgeneration is robust, quicker and more convenient, therefore it seems way mofrecompatible with all clinical aim. Objectives: The aim of this research is to create threedimensional finite element model of the TMJ comprising the bone components, both articular discs, and the temporomandibular ligaments, by using SCT and MRI scanning,3D reconstruction, image fusion, and finite element method. To create an ideal digitaltool for more profound research of TMJ. To simulate the lateral excursion of themandible and clenching on the model, and therefore study the biomechanical behavior ofboth TMJ sides. To create a system for predicting the TMJ discs deformation andperforation in case of TMD, trauma. To generate a3D visualization system for guidingTMJ surgeries, by which surgeons could realize the surgical planning, revising, and thepatient-doctor communication on the computer screen. Materials and methods:1)Application of different medical imaging techniques to acquire3dimensional image ofTMJ.①3D-CT scanning and reconstruction of the TMJ area of a normal individualobject. Continuous spiral CT scanning with a0.625mm/0.625mm scanning slice to anormal individual object, were generated on a GE Advantage CT scanning system. TheCT data were saved in DICOM format. MIMICS12.0soft ware was then used toreconstruct medical data. CAD models of facial bone, TMJ disc, and ligaments werereconstructed and optimized separately by MIMICS12.0, and saved in STL format.②MRI scanning and3D reconstruction of TMJ MRI scanning with a scanning slice of1.5mm to the same individual will generated. MIMICS12.0soft ware was also used toreconstruct the medical data.③Image fusion of TMJ medical imaging data from SCTand MRI scanning The contours of the cranium (temporal bone) and the mandible, softtissue (TMJ discs and ligaments) were obtained and matched by locating the marker ofthe individual’s face from both CT images and MRI images. Delicate adjusting wasgenerated according to the anatomical structure, and the image fusion were finished andsaved in STL format.2) Development of3D finite element model of the TMJ Thespecific conditions of boundary were set and the mesh of the TMJ area was manuallymade by using tetrahedrons on the basis of the medical image obtained from the imagefusion. According to different anatomical structures, the biomechanical features weredescribed in the mesh. Finite element model of the TMJ, comprising the bonecomponents, both articular discs, and the temporomandibular ligaments, was thendeveloped by means of ANSYS software package. A fibre reinforced porohyperelasticmodel was also introduced.3) Simulation of the lateral excursion and clenching ofmandible in the finite element model A lateral excursion of the mandible and clenchingwere introduced and the biomechanical behavior of both TMJ sides was studied. Themovement and the load of the articular discs and condylar were studied. The regularpatterns of TMJ discs were investigated under the symmetrical and non-symmetrical movement. Results:1) Application of different medical imaging techniques to acquire3dimensional image of TMJ.①3D spiral CT scanning and reconstruction of the TMJ areaof a normal individual Due to the high contrastability, spiral CT has great advantages inobtaining medical informations. Altogether465slices of TMJ area were acquired in ourresearch. About the segmenting and reconstructing CT images, MIMICS12.0(Materialise’s Interactive Medical Image Control System) are considered as an effectiveinteractive digital tool revealing. It could quickly and clearly reconstruct the complicatedstructure of the whole TMJ area. CAD models of temporal bone, mandible, articular discsand ligaments were built and optimized by all these reconstructed465slices from the3Dscanning. The acquired data were saved in the STL format, which could be directly inputinto ANSYS package for modeling and analysis.②MRI scanning and3D reconstructionof TMJ MRI has unique pre-dominance in obtainning the soft tissue image (articulardiscs and ligaments in this research).406slices of TMJ area were acquired in ourresearch. CAD models of articular discs and ligaments were built and optimized by thereconstructed465slices from the scanning. The acquired data were also saved in the STLformat.③Image fusion of TMJ medical imaging data from SCT and MRI scanning Thecontours of the cranium (temporal bone) and the mandible, soft tissue (TMJ discs andligaments) were obtained and matched by locating the11markers of the individual’s facefrom both CT images and MRI images. Delicate adjusting was generated according to theanatomical structure, and the image fusion were finished and saved in version of STLformat.2) Development of3D finite element model of the TMJ Mesh of cranium(temporal bone) and the mandible, soft tissue (TMJ discs and ligaments) was constructedmanually, which was combined with the tetrahedrons. There were40524elements and18263nodes in this mesh. Finite element model of TMJ, comprising the bonecomponents, both articular discs, and the temporomandibular ligaments was developedon the basis of mesh.65285elements and32341nodes were combined the finite elementmodel of facial soft tissue and reflected the biomechanical features (anisotropy,porohyperelastic and biphasic characteristics) in some respect and with certain accuracy.The model of TMJ created the basis and condition for the simulation of functionalmovements of TMJ, which consumed great amount of manual work, computation andtime.3) Simulation of the lateral excursion and clenching of mandible in the finiteelement model A lateral excursion of the mandible and clenching were introduced andthe biomechanical behavior of both TMJ sides was studied. The movement and the loadof the articular discs and condylar were studied. The regular patterns of TMJ discs were investigated under the symmetrical and non-symmetrical movement.As a consequence ofthe movement asymmetry, the discs were subjected to different load distributions. It wasobserved that the maximal shear stresses were located in the lateral zone of both discsand that the lateral attachment of the ipsilateral condyle-disc complex suffered a largedistortion, due to the compression of this disc against the inferior surface of the temporalbone. These results may be related with possible consequences of a common disordercalled bruxism. In clenching, the condyle moved upper, backward and interior, while thearticular discs turn forwards, as well as moving upper and backward with condyle. Thestresses of the discs are significantly lower than those of condyle, which pointing out thebuffering effect of the articular discs. Conclusions: This paper focus to create a digitalmodel of the TMJ on the basis of finite element method and image fusion technique,which was defined with biomechanical characteristics of TMJ. The finite element modelof TMJ comprised the bone components, both articular discs, and the temporomandibularligaments. The simulation of symmetrical and nonsymmetrical movement of TMJ wasgenerated on the finite element model, while the pattern of the load and movement ofboth the articular discs and condyle were acquired, which offered a solid scientific basisfor future clinical application. The results of the research revealed:1) The paper not onlyintroduced a full approach for developing a finite element model of TMJ area, but alsofocused on the simulation of the symmetrical and nonsymmetrical movement of TMJ. Aneffective digital tool for profound TMJ research was introduced.2) The paper addressedthe predominance of image fusion technique in acquiring the medical image, and itsfurther advantage in the development of finite element model. Image fusion allowed themore accurate data of the anatomical structure of the articular fossa, disc and condyle,which as a result, created a more accurate finite element model of TMJ.3) Thesimulation of the symmetrical and nonsymmetrical movement of TMJ, make the study ofthe regular patterns of the load and movement of both the condyle and the articular discpossible, which in return, offers a useful digital tools for the study of TMJ on the level ofboth physically and pathologically. The models fit the morphology of the individual, andthe prediction of TMJ disc deformation during movement was considered coherent withwhat they would expect.4) Finite element method is testified again helpfulness in TMJresearch, improving the TMJ surgery in certain degree, which may be widely applied inmedical field in future.