| Background:Class Ⅱ division 2 malocclusion is a common malocclusion,with the characteristics of severe lingual tipping of the upper anterior teeth and deep overbite.In these patients,forward growth and movement of the mandible are limited by the upper anterior teeth,which may affect the growth,development,and health of the TMJ.Therefore,the morphology,location and development characteristics of the TMJ in patients with Class Ⅱ division 2 malocclusion and changes of the TMJ in these patients during orthodontic treatment need further observation and research.The orthodontic treatment techniques commonly used in clinic mainly include traditional fixed appliance orthodontic technique and emerging clear aligner orthodontic technique.The effects of two technologies on TMJ of Class Ⅱ division 2 malocclusion patients need to be further studied.And clear aligner treatment,which has an occlusal splint effect caused by the thickness of the appliance patch,patients should wear clear aligners for a long time during the treatment,whether it will have an impact on the TMJ in patients with Class Ⅱ division 2 malocclusion is also a matter of clinical concern.The two-dimensional measurement of CBCT is more commonly used in clinical study of TMJ,the determination of the location of anatomical landmarks as well as the measurement of various indicators are carried out on a two-dimensional section.However,the three-dimensional(3D)spatial measurement directly locates the anatomical landmarks and measures each index on a reconstructed 3D model.Compared with the two-dimensional measurement method,it has the advantages of being more intuitive and more accurate and of making data collection easier.Objective:In this study,3D model reconstruction of CBCT will be carried out,and 3D spatial measurement method will be used to obtain a more specific and digital understanding of the TMJ morphology,position as well as the changes of the TMJ during orthodontic treatment of patients with Class Ⅱ division 2 malocclusion,which is intended to provide reference for the orthodontic clinical diagnosis and the formulation of program.Contents:1.Three-dimensional spatial analysis of the TMJ in different age groups of patients with Class Ⅱ division 2 malocclusion based on CBCT.2.Three-dimensional spatial analysis of the TMJ in adult patients with Class Ⅱ division 2 malocclusion before and after orthodontic treatment based on CBCT.Methods:1.The patients with Class Ⅰ malocclusion and Class Ⅱ division 2 malocclusion were included in the study.The two groups of patients were both divided into the adolescent group(12-18 years old)and the adult group(19-30 years old)according to age.The CBCT of TMJ in two types of patients of different ages was reconstructed and measured in 3D spatial measurement,statistical analysis was carried out on the data to study the TMJ morphology,location and growth characteristics of the patients with Class Ⅱ division 2malocclusion.2.The patients who have completed orthodontic treatment were included in the study.The CBCT of TMJ before and after orthodontic treatment was reconstructed and measured in 3D spatial measurement,statistical analysis was carried out on the data to study and analyze the changes of TMJ during orthodontic treatment,and to study the similarities and differences of the effects between fixed appliance treatment and clear aligner treatment on TMJ.Results:1.The TMJ data measured in patients with Class Ⅰ malocclusion and Class Ⅱ division 2 malocclusion were statistically analyzed.(1)General data: A total of 120 patients were included in the experiment,including60 patients with Class Ⅰ malocclusion(31 adolescents and 29 adults)and 60 patients with Class Ⅱ division 2 malocclusion(30 adolescents and 30 adults).There was no statistical difference in gender or age between the two groups,and there was basically no statistical difference in TMJ measurements on the left and right sides of the patients.(2)Measurement analysis of CBCT data shows that: The glenoid fossa size,condyle volume and surface area of male patients were higher than those of female patients,the sagittal condyle angle was less than that of female patients(P < 0.05).With the increase of age,the anterior joint space,superior joint space,interior joint space,exterior joint space,fossa depth,inner and outer diameter,anterior and posterior diameter,volume and surface area of the condyle increased in patients with Class Ⅰ malocclusion(P < 0.05),and the superior joint space,exterior joint space,inner and outer diameter,anterior and posterior diameter,volume and surface area of the condyle increased in patients with Class Ⅱ division 2 malocclusion(P < 0.05).There were significant differences in anterior joint space,posterior joint space,fossa width,depth,height of the condyle,inner and outer diameter,anteroposterior diameter,volume and surface area of the condyle between patients with Class Ⅰ malocclusion and Class Ⅱ division 2 malocclusion(P < 0.05),The condyle in the glenoid fossa was mostly located in the middle position in patients with Class Ⅰ malocclusion,and a large proportion of patients with Class Ⅱ division 2malocclusion the condyle was retro-displaced.2.The TMJ data of patients with Class Ⅱ division 2 malocclusion measured before and after orthodontic treatment were statistically analyzed.(1)General data: CBCT data of 42 adult patients with Class Ⅱ division 2malocclusion(22,fixed appliance group;20,clear aligner group)were collected before and after treatment.There were no significant differences in sex and age between the two groups,and no significant differences in the measurement values of the left and right sides of the joints between the groups before and after treatment.(2)Measurement analysis of CBCT data shows that: After fixed appliance treatment,the changes of anterior joint space,posterior joint space,fossa width,anterior and posterior diameters,internal and external diameters,volume,and surface area of the condyle were statistically significant.After clear aligner treatment,the changes of anterior joint space,posterior joint space,fossa depth,anterior and posterior diameters,internal and external diameters,volume,and surface area of the condyle were statistically significant.The results of the comparison of TMJ-related structural changes after fixed appliance and clear aligner treatments were as follows: there were significant differences in the measurement values of the superior joint space,fossa width,fossa depth,and interior joint space(P < 0.05).The condyle position in the articular fossa was compared before and after orthodontic treatment in adult patients with Class Ⅱ division 2malocclusion.About 38% patients with fixed appliance treatment moved forward to the center of the glenoid fossa,while about 45% patients with clear aligner treatment moved forward.Conclusions:1.The condyle of male patients is slightly backward in the glenoid fossa than that of female patients,and the width and overall size of male condyles are also larger than that of female patients.There was no significant difference in internal and external diameters of the condyle between the two groups of juvenile patients,while the condyle volume and surface area of the adult patients with Class Ⅰ malocclusion were larger than those with Class Ⅱ division 2 malocclusion.From the perspective of glenoid fossa morphology,the glenoid fossa of patients with Class Ⅰ malocclusion was wider,and the glenoid fossa of patients with Class Ⅱ division 2 malocclusion was narrower and steeper.In terms of the condyle location,the condyle was mostly located in the center of the glenoid fossa in patients with Class Ⅰ malocclusion,but in patients with Class Ⅱ division 2 malocclusion,the condyle was mostly located in the posterior displacement.2.Whether fixed appliance treatment or clear aligner treatment,after orthodontic treatment,the inner and outer diameter,anterior and posterior diameter,volume and surface area of the condyle increased to a certain extent,and most patients’ condyle shifted forward and was located in the center of the fossa.After fixed appliance treatment,the width of the glenoid fossa increased.After the clear aligner treatment,the superior joint space and the depth of the glenoid fossa increased,while the superior joint space and the depth of the glenoid fossa did not change significantly after fixed appliance treatment. |
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