| BackgroundTemporomandibular joint in the anatomy or physiology function, is one of the body’s most complex joints. Temporomandibular joint stress distribution in the region has an important impact on the joint development and maintenance of the normal anatomy of the temporomandibular joint structure and function. Because of the complexity and flexibility of temporomandibular joint motor function, often caused by changes in the temporomandibular joint internal stress distribution may lead to temporomandibular joint disorder, and even structural damage to the joints inside. High incidence of temporomandibular joint disorder with the morbidty about 20%.Current research shows that:the Movement of lateral pterygoid muscles are close to the temporomandibular joint disc, and played an important role on maintaining the stability of the temporomandibular joint movement. As we all know, the lateral pterygoid muscles dysfunction can lead to temporomandibular joint disorder. Early research on the lateral pterygoid muscles description is relatively simple, the lateral pterygoid muscles are considered as a whole, starting in the outer wing panels and temporal below, beyond the condyle, joint capsule and articular disc, and then with the domestic and foreign scholars for a more detailed anatomical study on the lateral pterygoid muscles, that it has a clear head up and down at the start and end points of the upper and lower fascia have their head wrapped in the middle of adipose tissue apart and buccal nerve through, on top of part of the attachment the joint disc surface, part of the condyle.Temporomandibular joint disorder biomechanical has been one of the hot research scholars, former joint disc displacement also has a wealth of research, but look at the literatures on the anterior disc displacement of the temporomandibular joint system The study uses the masseter muscle loading or chewing muscles loaded system. In the study of masticatory muscle system load, the load for the lateral pterygoid muscles are loaded only inferior head of the muscle strength, and without taking into account factors on superior head of the lateral pterygoid muscles. Lateral pterygoid muscles played an important role on the temporomandibular joint movement, it is necessary to concern on the role of biomechanical research of lateral pterygoid muscles on the temporomandibular joint area under the accurate positioning of lateral pterygoid muscles.ObjectiveThis experiment using computed tomography (CT) scanning technology, three-dimensional reconstruction, reverse and finite element calculation of engineering software:Free Form, Mimics, Geomagic, Solid works, ANSYS Workbench, etc., was established by a digital simulation model of temporomandibular joint with anterior disc displacement, to expplain the biomechanics pathogenic mechanism law ang function of each anatomical structure on the temporomandibular joint; Through the establishment of finite element model, reveal the different characteristics in the reconstruction of the temporomandibular joint with anterior disc displacement models, for the development the relationship of the temporomandibular joint with anterior disc displacement and the lateral pterygoid muscles to provide laboratory data support.Materials and MethodsPart Ⅰ:The establishment with anterior displacement of the temporomandibular joint disc digital simulation model with lateral pterygoid muscles.1. The model data source:Based on experimental purposes and the diagnostic criteria for temporomandibular disorders, screening the right of an adult male patients with temporomandibular joint disorder,26, a history of six months, no history of trauma surgery, dentition occlusion cmoplete, neutral together, no history of joint disease.2. Data acquisition mode:64-slice CT SIEMENS company continuously scan the patient temporomandibular joint area. Scanning parameters:thickness 0.5mm, seeking tube current 200mA, voltage 120KV; using 3D-MR consecutive patients oblique sagittal plane sweep temporomandibular joint area. Scanning parameters:thickness 0.5mm, T1W1 sequence, layer spacing 0mm. Scanning range from the right side of the skull base to the lower edge of the right side of the mandible, the obtained data in DICOM format.3. Temporomandibular joint three-dimensional finite element model of the simulation:the use of CT and 3D-MR scan Dicom format of the input image data reconstruction software Mimics (Materialise Belgian company), and were treated to establish cortical mandible, condylar cortical bone, and cartilage layer, articular disc, articular fossa, the articular disc and condyle cartilage, and then to export the STL file format and enter into reverse engineering software Geomagic software, anatomical structure of image segmentation, fine finishing three-dimensional space, the corner portion smooth structure smooth surface treatment. After a series of smooth, polished, de-noising and other image processing to generate a three-dimensional graphics file formats IGES, hard and soft tissues of the temporomandibular joint reset exact match to get the overall reconstruction of the temporomandibular joints in hard and soft tissues of the system. Reserch projects through 3d-MR images to determine precise of the lateral ptergoid muscles attachmennt sites, using 15-20 ptergoid muscles bundle to reconstruction the lateral ptergoid muscles in the three-dimensional finite element model.Part Ⅱ:Biomechanical analisis of the temporomandibular joint with anterior disc displacement on intercuspal position with the load of lateral ptergoid muscles.1. The boundary conditions:within the glenoid fossa of the temporomandibular joint center upper range fixed constraints, and in order to prevent the occurrence of a rigid displacement of the mandible, it limits the movement of the mandible, the bottom section of the degrees of freedom into the normal constraints and apply frictionless constraints, static mechanical finite element analysis.2. The contact settings:in Workbench, mandibular cortical and cancellous bone is completely fixed, when dealing with it as a whole; on the condylar surface and lower surface of the condylar cartilage layer bonded contact; under the surface of the glenoid fossa and on the surface of the glenoid fossa cartilage layer bonded contact; articular disc, respectively, on the lower surface of the condylar cartilage and glenoid cartilage surface of the friction coefficient of frictional contact 0.001.3. Lateral pterygoid muscle load:Analog pterygoid muscle strength in the direction of intercuspal position will be divided into two lateral pterygoid muscles. Muscle load on superior hend of muscle was laod on the disc and condyle articular surface, the inferior head was loaded on the mandibular condylar neck muscle nest, loading force were:11.4N and 33.84N.4. Temporomandibular joint biomechanics analysis:lateral pterygoid muscles were loaded, TMJ analysis model to calculate the intercuspal position and displacement analysis of temporomandibular joint articular disc, glenoid fossa, mandibular cortical bone, cancellous bone, glenoid fossa and condyle biomechanical characteristics stress and displacement trends.Part Ⅲ:Biomechanical analysis of the temnporomandibular joint with anterior displacement on opening position with the load of lateral pterygoid muscles.1. The boundary conditions:within the glenoid fossa of the temporomandibular joint center upper range fixed constraints, and in order to prevent the occurrence of a rigid displacement of the mandible, it limits the movement of the mandible, the bottom section of the degrees of freedom into the normal constraints and apply frictionless constraints, static mechanical finite element analysis.2. The contact settings:in Workbench, mandibular cortical and cancellous bone is completely fixed, when dealing with it as a whole; on the condylar surface and lower surface of the condylar cartilage layer bonded contact; under the surface of the glenoid fossa and on the surface of the glenoid fossa cartilage layer bonded contact; articular disc, respectively, on the lower surface of the condylar cartilage and glenoid cartilage surface of the friction coefficient of frictional contact 0.001.3. Lateral pterygoid muscle load:Analog pterygoid muscle strength in the direction of opening position will be divided into two lateral pterygoid muscles. Muscle load on superior hend of muscle was laod on the disc and condyle articular surface, the inferior head was loaded on the mandibular condylar neck muscle nest, loading force were:11.4N and 33.84N.4. Temporomandibular joint biomechanics analysis:lateral pterygoid muscles were loaded, at the cusp of the temporomandibular joint staggered effect model to calculate the force and displacement analysis, analysis of temporomandibular joint articular disc, glenoid fossa, mandibular Mechanical characteristics of biological stress cortical cancellous bone, joint and condylar fossa,and the displacement trends.Using CT precision scanning acquisition healthy adult volunteers mandibular data, through 3 d reconstruction software Mimics successfully established normal mandible 3 d entity model, the model contains the complete denture, cancellous bone and cortical bone, and has good geometric similarity.Results1. Using CT and 3D-MR precision scaning acquisition front reusable disc displacement of the temporomandibular joint disorders temporomandibular joint adult volunteers to the right data, through a three-dimensional reconstruction software Mimics successful established a intercuspal and opening position three-dimensional solid model with temporomandibular joint disc displacement, the model includes the articular disc, joint capsule, condyle, glenoid fossa, mandibular cortical bone, and have good geometric similarity.2. Biomechanical analysis of the temnporomandibular joint with anterior displacement on intercuspal position with the load of lateral pterygoid muscles.2.1. Temporomandibular joint stress equivalent overall distribution:the intercuspal position of temporomandibular joint overall maximum equivalen stress appear at the mandibular angle:below the neck of mandibular condyle and above the sigmoid notch, the maximum stress value was 28.8MPa; on the mamdible bone, the stress gradually decreasing from the surrounding areas of stress concentration; on the mandibular trabecular bone area, the stress concentration in the condylar neck, and the maximum stress is 5.3MPa, significantly reduced compared with cortical bone stress; glenoid fossa and condyle of the maximum stress occurred at the function with respect to the structure of the surface contact.2.2. The overall displacement of the temporomandibular joint distribution: the maximum displacement of temporomandibular joint area was occurs in the front part of the joint capsule, on top of the lateral pterygoid muscles attachment area, the maximum displacement of 1.80mm; the displacement since the mandibular anterior attachment to the middle of the disc was increasing, but since the middle of the disc to the after attachment the displacement was gradually decreasing;mandible and the temporal bone area of displacement is not obvious, the displacement of mandibular was mainly apear in the mandibular condylar, and the displacement size of 0.50mm.2.3. The equivalent stress distribution in the temporomandibular joint disc: the largest equivalent stress distribution of the articular disc regionwas concentration on the middle region of articular disc, and the maximum stress is 3.0MPa, the stress distribution since the mandibular anterior attachment to the middle of the disc was increasing, but since the middle of the disc to the after attachment the displacement was gradually decreasing;3. Biomechanical analysis of the temnporomandibular joint with anterior displacement on opening position with the load of lateral pterygoid muscles.3.1.Temporomandibular joint stress equivalent overall distribution:the intercuspal position of temporomandibular joint overall maximum equivalen stress appear at the mandibular angle:below the neck of mandibular condyle and above the sigmoid notch, the maximum stress value was 34.5MPa; on the mamdible bone, the stress gradually decreasing from the surrounding areas of stress concentration; on the mandibular trabecular bone area, the stress concentration in the condylar neck, and the maximum stress is 5.3MPa, significantly reduced compared with cortical bone stress; glenoid fossa and condyle of the maximum stress occurred at the function with respect to the structure of the surface contact.3.2. The overall displacement of the temporomandibular joint distribution: temporomandibular joint area of maximum displacement occurs in the front part of the joint capsule, on top of the load of lateral pterygoid muscles attachment area, the maximum displacement of 1.41mm; the displacement since the mandibular anterior attachment to the middle of the disc was increasing, but since the middle of the disc to the after attachment the displacement was gradually decreasing; mandible and the temporal bone area of displacement is not obvious, the displacement mainly in the mandibular condylar, displacement size of 0.50mm.3.3. The equivalent stress distribution in the temporomandibular joint disc: the largest concentration stress of the joint was o in the middle region of the lateral side disc with a maximum stress is 1.17MPa, the stress distribution since the middle of the articular disc belt attached to the front side and the lower jaw and after the attachment area gradually decreasing; anterior condylar plate in contact with the jaw attachment region also appeared stress concentration area.Conclusion1. CT and 3D-MR scans get to the right temporomandibular joint hard and soft tissue data, combined with the use of three-dimensional reconstruction software Mimics reverse engineering software to build a three-dimensional finite element model can be reset before the joint disc displacement. Reverse engineering software for temporomandibular joint model making the model more realistic, the various parts of the model can be together as a whole, they can be analyzed separately, and close to clinical practice, can be more accurate biomechanical characteristics of temporomandibular joint area.2. The posterior-lateral function and biaminar tape of the psedu 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, during the functional treatment of the anterior disc displacement, not only the release of the posterior belt and biaminar region but also the relax of the anterior adherent of the condyle shouid be focused.3. Under the lateral pterygoid muscles action with anterior displacement of the articular disc of temporomandibular joint biomechanical analysis showed: conform the temporomandibular joint biomechanics visible:the maximum stress occurs in the middle of the articular disc with partial lateral area, but also in the displacement analysis can be found in this area, there has been a shift in this area with a tear, suggesting that the role of lateral pterygoid muscles may lead the joint disc with stress concentration and displacement has occurred tear, This area leads to thinning and even perforation. |
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