| OBJECTIVE:Temporomandibular joint is the only joint in skull.The changes of temporomandibular joint are very important for the stability of operation and the function of patients after operation during SSRO retrogression.However,the changes of temporomandibular joint after operation and the mechanical changes of temporomandibular joint after the change of muscle function balance are not very clear.In this study,three-dimensional reconstruction of spiral CT and identification of soft and hard tissues by CT and MRI were used for finite element analysis.To explore the changes of temporomandibular joint area after SSRO and its influence,and to provide experimental basis for clinical and treatment.METHODS:In experiment 1,13 patients with bone type III were enrolled in the orthognathic center of the Affiliated Stomatological Hospital of Guangxi Medical University,including 4 males and 9 females,with an average age of 23.4years,the youngest age being 18.8 years and the oldest age being 27.6 years.Selection criteria:The patients in this study were skeletal class III malocclusion,ANB<0,SNB>80,with or without deformity of the jaw.In addition,we must meet the following conditions:(1)Before and after the operation,the patient is in good health and has no systemic diseases;after the operation,there are no serious complications such as infection,bone fracture and so on.(2)According to the bone age score of cervical spine,the growth and development of cervical spine is over.(3)Perfect preoperative orthodontics,follow the orthodontic-surgical-orthodontic conventional surgical methods.The operation was performed by the same team.Each patient was photographed with spiral CT one week before operation,one week after operation and one year after operation.Twenty-six temporomandibular joints were reconstructed with MIMICS 20.0.They were divided into three groups according to pre-operation and post-operation(T0-T1),post-operation recovery(T1-T2)and post-recovery comparison(T0-T2).A total of 78 temporomandibular joints were divided into three groups.The rotation angle of the condyle,the volume of the condyle,and the changes of the temporomandibular joint space were measured according to the anterior,transverse and posterior oblique surface of the condyle.Only the experimenter himself measured the research project and completed it at the same time.The same measurement method was carried out for the second time after 2 weeks.The results of the two measurements were calculated by intra-group correlation coefficient.If ICC was greater than 0.75,the mean values of the two measurements were taken.SPSS 18.0 was used for statistical analysis,and paired design t test was used to compare the differences of each group.The test level was alpha=0.05.Experiments 2.In order to investigate the stress of the newly established occlusal relationship and the change of the dynamic balance of the muscles in the jaw-mandibular relationship,a finite element model was established to analyze the stress.A 21.6-year-old man with mandibular protrusion deformity was selected as the specimen.The patients underwent BSSRO after orthodontic decompensation before operation.Selection criteria are as follows:(1)BSSRO operation;(2)unbiased jaw;(3)no pre-operative and post-operative symptoms of temporomandibular joint;(4)good recovery after operation,no serious surgical complications such as infection and osteonecrosis;(5)MRI and spiral CT were taken one week before operation,and CT was taken one week after operation.The skeletal structure was identified by CT,while the soft tissue structure including the orifice-closing muscle group,articular disc and temporomandibular ligament was identified by MRI.The mechanical models before and after operation were established by MIMICS,HYPERWORK,ABAQUSand GEOMAGIC,and the force changes during occlusion and opening of temporomandibular joint were simulated.The results of Experiment 1 were compared to find out the effect of muscle dynamic balance on the regional changes of temporomandibular joint after SSRO.Result:The condyle was transverse,T0-T1 was rotated inward 7.241±3.835°,T1-T2 was rotated outward 2.043±2.753°,T0-T2 was rotated outward5.199±4.079,,there was no significant difference between the condyle and coronal rotation,there was no statistical significance in the condyle rotation on the coronal plane;the condyle external pole moved forward 2.269±1.736mm during T0-T1,T1-T2 move back 0.942±1.364mm mm,move superior0.668±1.259mm during T0-T2.There was no significant difference in the displacement of the remaining exterior poles.During T0-T1,the inner pole shifted0.986±1.329mm to the lateral side,1.266±1.428mm to the downward side.0.675±0.769mm to the medial side,0.796±1.448mm to the upward side,and0.484±0.960mm to the backward side during T0-T2.During T0-T1,the joint spaces of medial oblique plane,medial transverse ridge of condyle,medial transverse ridge,medial transverse ridge,lateral transverse ridge and posterior oblique plane of condyle process increased.During T1-T2,the joint spaces of medial oblique plane,medial transverse ridge,medial transverse ridge and lateral transverse ridge decreased.During T0-T2,the joint spaces of medial transverse ridge and middle transverse ridge of condyle process increased.The difference was statistically significant.The volume of condyle changed during T0-T2.The average volume of condyle at T0 was 1183.79±276.76mm~3 and decreased to1147.22±272.22mm~3 at T2.The difference was statistically significant.The height of the middle part of the condylar transverse ridge of T0-T2 decreased,but there was no statistical significance.The results of finite element analysis show that in the stress of the articular disc,comparing the pre-and post-operative stress values,it can be found that there is little difference between the maximum stress before and after surgery,and the maximum stress on both sides before surgery is different.The position of the stress center on the upper and lower sides of the disk changes,the lower stress center moves forward,and the upper side moves backward.In the stress of the condyle,the stress of the joint head is directed to the inner side at the time of opening,and the stress is slightly decreased at the small opening.The maximum stress in the temporomandibular ligament region was reduced compared with preoperative,and there was no significant difference in stress distribution.CONCLUSION:The morphology and location of temporomandibular joint region have changed after SSRO,and the balance of muscle dynamics has changed. |
PDF Full Text Request