| Background:temporomandibular joint disorder is a kind of disease with the main manifestations of joints clicking,pain and trismus.Once the disease developed to the serious organic destruction stage with perforation of articular disc and condylar resorption,it would cause the mandibular deviation or retraction.It is also a common disease from the perspective of epidemiology.It is reported that the incidence of the disease is as high as 20%-25%.However the cause of the disease cannot be found in time clinically,it leads to the fact that the treatment of the disease can only be carried out with the emergence of organic lesions.And the treatment is only an alleviation for the symptoms,not clinical cure.Therefore,early detection of the factors leading to temporomandibular joint pathological changes and causes of the risk,taking effective intervention,and then stopping or even reversing the pathological changes of temporomandibular joint internal derangement are the keys to prevention of temporomandibular disorders.Objective:this study collected the CBCT and MRI images of the joints of the normal persons in normal occlusion and malocclusion.We built the construction of the digital 3D model under the condition of rotating force and rotation to measure the relationship between condyle,articular disc and glenoid fossa.Then we get the normal biomechanical parameter database of the temporomandibular joint and the database of the relationship between the rotation force and the rotation of the disc.At last we compared the parameters of the temporomandibular joint with the database to analyze the relationship between the position of condyle,articular disc and glenoid fossa and joint load.Methods:20 volunteers were selected from the medical school of Zhejiang University(8 males,12 females,age averaging 25.6 years old).All of the volunteers would be taken craniofacial CBCT and MRI.All volunteers were informed consent.The volunteers were enrolled according to the following selection criteria:both sides of the joints with no snapping or pain;open type,open degree is normal;no history of limited mouth opening;no orthodontic treatment history;no missing teeth in the mouth;neutral molar relationship;no malocclusion;no deep overbite or deep overjet;upper and lower midline deviation is less than 1mm.MRI and CBCT tomographic images of 20 volunteers were imported into Mimics 17.With the function of automatic definition of four directions:left and right,anterior and posterior,then manually define the upper and lower direction.The software will automatically generate coronal and sagittal images based on cross sectional images.Translate the two-dimensional MRI image directly into a three-dimensional model with the use of three-dimensional software tools,the Calculate menu in the partition 3D.The reconstructed 3D model is saved in STL format,and the reconstructed 3D visualization model of MRI is used to observe the structure of the articular disc and surrounding tissues.At last,according to the matching relationship of the TMJ soft and hard tissue anatomical position,the final overlapping three-dimensional model is formed.The reconstructed model can be translated,scaled,rotated at any angle and cut in any plane,and the three-dimensional shape of the temporomandibular joint,articular disc and condyle can be directly and clearly reconstructed.SPSS 15 statistical software was used to test the results.Independent samples t-test was used to analyze whether there are differences between before and after.Independent samples t-test was used to analyze whether there are differences in mandibular deviation after disc displacement and angle and distance,the articular disc after displacement angle and distance,disc rotation displacement angle and the distance of mandibular anterior.Results:the horizontal condylar angle of the left side of the joint was 18.5150± 4.8026 degrees slightly lower than the level of the mandibular condyle at the angle of 19.4725± 5.4211 degrees,but there was no significant difference(*P>0.05).The left joint posterior condylar angle 10.3413±3.2124 degrees is slightly larger than the anterior condylar angle 7.7975±4.1136 degrees,but no significant difference(*P>0.05).The angle of rotation of the articular disc of the left side of the joint is 7.6363±1.3217 degrees,which is obviously greater than the angle of the rotation of the anterior articular disc,which is 3.6788±0.6457 degrees(*P<0.05).The displacement of the joint disc rotation of the left side of the joint was 0.5650±0.1376mm,which was significantly greater than that of the anterior disc displacement 0.27000±0.0711mm(*P<0.05).The horizontal condylar angle of the right side of the joint was 16.9013±8.7832 degrees slightly larger than that of the mandibular condyle before and after the mandibular condyle angle was15.6088±6.5628 degrees,but there was no significant difference(*P>0.05).Right jaw joint posterior condylar angle 7.2200±6.4185 degrees is slightly larger than the anterior condylar angle jaw 4.1400±2.6491 degrees,but no significant difference(*P>0.05).The lateral joint space of the right side of the joint was 3.5175±0.8145mm,which was significantly larger than that of the lateral joint space of the anterior part of the mandible 2.3675±1.0746mm(*P<0.05).The upper joint space of the right side of the joint was 5.5900±4.3116mm,which was significantly larger than that of the lateral joint space of the anterior part of the mandible 2.1475±0.5792mm(*P<0.05).The posterior joint space of the right side of the joint was8.0263±3.9708mm,which was significantly larger than that of the posterior joint space of the anterior part of the mandible 3.5488±1.5137mm(*P<0.05).The angle of the medial and lateral displacement of the posterior articular disc of the right side of the joint was 5.3738±0.7457 degrees,which was significantly greater than that of the anterior and posterior disc displacement of the temporomandibular joint 4.1988±0.5697(*P<0.05).The distance between the medial and lateral displacement of the joint of the right side of the mandibular joint was 0.6313±0.0797mm,which was significantly greater than the distance between the anterior and posterior disc rotation of the mandible 0.5213±0.0647mm(*P<0.05).The angle of the anterior and posterior disc displacement of the right side of the joint was 8.7325±2.6722 degrees,which was significantly greater than that of the anterior and posterior disc of the mandibular joint.The angle was about 4.3450±1.4898 degrees(**P<0.01).The angle of deformation of the articular disc of the right side of the joint was 85.5663±1.2631 degrees,which was significantly greater than that of the anterior mandibular joint.The angle of deformation of the articular disc was 80.8300±2.3811 degrees(**P<0.01).The angle of rotation of the joint disc of the right side of the joint was 6.1463±0.8573 degrees,which was significantly higher than that of the anterior mandibular joint.The angle of rotation of the joint disc was 3.8138±0.3807 degrees(*P<0.05).The displacement of the posterior articular disc of the right side of the joint was 0.5613±0.0951mm,which was significantly greater than the displacement of the anterior disc displacement of the temporomandibular joint 0.2750±0.0484mm(*P<0.05).Conclusions:the angle and distance of the disc rotation of the left side of the joint were significantly larger than those of the anterior part of the mandible and there is no significant difference in the level of horizontal condylar angle and coronal condylar angle.The lateral space of the right side of the joint of the right side,the upper joint space and the posterior joint space were significantly larger than that before.The angle and distance of the medial and lateral displacement of the articular disc of the right side of the joint,the angle of the anterior and posterior displacement of the articular disc,the angle and distance of the rotation displacement of the articular disc,and the angle of the deformation of the articular disc were larger than those before. |
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