CBCT Study Of Mandibular Symphysis And Lower Incisor Position In Adult Skeletal Class Ⅱ Malocclusion

Objective Using CBCT three-dimensional imaging technology to study the mandibular symphysis and the position of lower incisor of different genders and different vertical skeletal bone types in adult skeletal class Ⅱ malocclusion,and to explore the correlation between lower incisor inclination and mandibular symphysis.The purpose of this study is to provide relevant data support for the selection of orthodontic treatment,lower incisor movement and prognosis judgment for skeletal class Ⅱ patients.At the same time,it also provides a certain clinical diagnosis and treatment value for the aesthetics of the lower 1/3 of the face.Methods According to the inclusion criteria,60 adult patients with skeletal class Ⅱ were selected as the experimental group,aged from 18-30 years,with an average age of 23.7years.30 adult patients with skeletal class I were selected as the control group,aged from 18-30 years,with an average age of 23.4 years.The experimental group and the control group were divided into three groups according to the size of FMA: high angle group,average angle group and low angle group.There were 20 cases in each group,half male and half male.There were 10 cases in each group in the control group,half male and half female.Using Invivo Dental 5.0 software,the CBCT image data are imported to measure the data.The measurement items include:(1)H(mm);(2)W(mm);(3)H/W;(4)Id-B-Pog(°);(5)B-Pog-Me(°);(6)Idm-Me-MP(°);(7)L1-MP(°);(8)LA(mm);(9)LP(mm);(10)LA+LP(mm).All measurement items were measured by myself three times at intervals of one week,and the average value was taken,and the data analysis was completed by using SPSS 24.0 statistical software.(1)Compare the mandibular symphysis and the position of the lower incisors between the experimental group and the control group;(2)compare the differences of mandibular symphysis and lower incisor position of different genders and different vertical bone types of skeletal class Ⅱ malocclusion;(3)Analyze the correlation between the inclination of lower incisors and the measurement items of mandibular symphysis.The test level is α = 0.05.Results(1)In the low angle facial types,the L1-MP and Idm-Me-MP of the experimental group were larger than those of the control group,and the LP was smaller than that of the control group.In the average angle and high angle facial types,the L1-MP of the experimental group was larger than that of the control group.There was a statistical difference(P<0.05),and no statistical difference was found in the rest of the measurement data(P>0.05);(2)There was no statistically significant difference in the measured dates of skeletal type Ⅱ patients between different genders(P>0.05);(3)In skeletal class Ⅱ malocclusion: There were statistical differences in H,W,H/W,Id-B-Pog,Idm-Me-MP,LA,LP,LA+LP,L1-MP among different vertical bone surface types(P<0.05).The results of pairwise comparison showed that: H,H/W decreased gradually in high angle,average angle and low angle groups,and L1-MP,LA,LA+LP increased gradually in high angle,average angle and low angle group.and the difference was statistically significant(P< 0.05);The Id-B-Pog in the high angle group was larger than that in the low angle group,and the LP,W,and Idm-Me-MP in the high angle group were smaller than that in the average angle group and low angle group,and the difference was statistically significant(P<0.05).(4)L1-MP was negatively correlated with H,H/W,and Id-B-Pog,but positively correlated with W and Idm-Me-MP(P<0.05),and significantly correlated with H/W and Idm-Me-MP.Conclusion(1)the sagittal bone surface type has little effect on the shape of the mandibular symphysis and the thickness of the alveolar bone in the lower incisor area.but has a greater effect on the inclination of the lower incisor;(2)there is no significant difference in the mandibular symphysis and the position of the lower incisor between different genders;(3)the mandibular symphysis and the position of the lower incisor in skeletal class Ⅱ malocclusion vary greatly among different vertical bone surface types.That is,in patients with high angle type,the mandibular symphysis is narrow and long,the concavity and convexity of the symphysis are relatively flat,the thickness of the alveolar bone in the apical area of the lower incisor is relatively weak,and the range of movement of the lower incisor is limited.More attention should be paid to patients with skeletal class Ⅱ high angle in clinical practice.(4)During growth and development,changes in the inclination of the lower incisors may affect the shape of the mandibular symphysis.(5)before orthodontic treatment,the mandibular symphysis and the compensatory mechanism of alveolar bone in the lower incisor area should be fully understood and evaluated comprehensively so as to make the diagnosis and treatment of skeletal class Ⅱ patients more safer and effective.