Morphological Analysis Of Temporomandibular Joint In Average Angle Adults With Two Types Of Skeletal Class Ⅱ Malocclusion

Object:The experiment aims to compare the morphology and size of the temporal-mandibular joints and the location parameters of condyles in the glenoid fossa of average angle adults with steletal class II division 1 malocclusion and steletal class II division 2 malocclusion through cone beam computed tomography(CBCT),and provide a reference for orthodontic diagnosis and treatment.Method:A total of 87 subjects were chosen and divided into three groups according to their ANB angle,GOGN-SN angle and Angle’s classification:group A:class II division1 malocclusion group(30 cases in total,including 15 males and 15 females);group B:class II division 2 malocclusion group(29 cases in total,including 14 males and 15females)and control group C:class I normal occlusion group(a total of 28 cases,including 15 males and 13 females).All patients underwent CBCT scan with maximum occlusal intercuspidation before treatment.The CBCT files of DICOM format were imported and reconstructed in three dimensions based on an equal proportion by MIMICS software,and then the head position was adjusted and the volume and surface area of the reconstructed condyle were measured.With the maximum cross-sectional area of axial condyle and the oblique sagittal position selected as the reference plane of the measurement,axial condylar surface area(ms),the long axial diameter(l)and horizontal angle(β)of processus condyloideus and the radius(r)of temporal-mandibular joint were measured on the axial plane.The height(h)and width(d)of the glenoid fossa,the inclination angle of the post-articular tubercle(α),the superior joint space(UU’),the anterior joint space(AA’),and posterior joint space(PP’)were measured on the oblique sagittal position.The position of the condyle in the glenoid fossa was calculated according to the Pullinger A linear ratio formula(LR)=(P-A)/(P+A)*100.Each measurement item was measured for 3 times and the average value was taken.All measured data were entered into the SPSS 17.0software so as to conduct pair t-test to the measurement indexes of the left and right temporal-mandibular joint structures of group A,B and C,perform a single factor analysis of variance on the measured values of their temporal-mandibular joints,and make SNK-q paired comparison among the statistically significant measurement items.Results:Through analyzing the CBCT data of average angle adult with Skeletal Class II Malocclusion,the following results are obtained:1.There was no statistical significance about the differences of parameters at both the left and right temporal-mandibular joints of the three groups(P>0.05).2.The difference in the inclination angle of the post-anterior fossa and posterior joint space of the three groups was of statistical significance(P<0.05).3.The differences between class II division 1 malocclusion and those with class II division 2 malocclusion and class I normal occlusion in the long axial diameter of condyle and superior joint space were all of remarkably statistical significance(P<0.05).4.The differences between the average angle adults with class II division 2 and those with class I normal occlusion and class II division 1 malocclusion in the anteroposterior diameter of the condyle,the height and width of the glenoid fossaand anterior joint space were all of statistical significance(P<0.05).The difference between the average angle adults with class II division 2 malocclusion and those with class I normal occlusion in condylar inclination angle showed a statistical significance(P<0.05).5.The LR value showed that the condyles of 65%average angle adults with class II division 1 malocclusion were in the anterior position,20%in the medium position and only 15%in the posterior position.The condyles of 17%average angle adults with class II division 2 malocclusion were in the medium position and 83%in the posterior position,and the condyles of 55% average angle adults with class I normal occlusion were in the medium position,29%in the anterior position and 16%in the posterior position.Conclusions:The condyles of the average angle adults with class I normal occlusion are mostly in the medium position of the glenoid fossa,those of the average angle adults with class II division 1 malocclusion are mostly in the anterior position,while those of the average angle adults with class II division 2 malocclusion are largely in the posterior position.The condyles of average angle adults with class II division 2malocclusion are mostly in the functional posterior position and it may be applied in clinical orthodontics.