Analysis Of Influencing Factors On The Angulation And Eruption Space Of Mandibular Third Molar In Orthodontic Patients

Objective:To analyze the influencing factors of the inclination angle and the eruption space of the mandibular third molar before and after the treatment of orthodontic patients aged 12-21,and to predict the inclination angle of the mandibular third molar after correction,which provides a reference for the orthodontist to develop the correction plan.Method:70 cases of orthodontic patients,aged 12-21 years,were selected from the orthodontic department of the Affiliated Stomatological Hospital of Nanchang University from 2014 to 2018,including 39 cases of extraction(minus 4 first premolars),female 20 cases,19 males;31 cases of non-extraction,16 females and 15 males.CBCT scans were performed on patients before(T1)and after(T2).Threedimensional reconstruction and head position correction of CBCT before and after treatment were performed by Invivo Dental 5.0 software.The near-middle tilt angle of the mandibular third molar and related measurement items were taken and the measured data were recorded into SPSS 21.0 software for statistical analysis.According to gender,age,mandibular plane angle(T1),ANB angle(T1),the ratio of the distal space of the mandibular second molar and the crown width of the mandibular third molar(abbreviated as RI ratio)and whether or not the extraction was an independent variable,Multiple linear regression analysis was performed for the following changes in the mesial third molars(?M3-?FH)and RI ratio change(?RI)as dependent variables.Results:1.The change of the inclination angle of the third molar(?M3-?FH)is the dependent variable,and the multiple linear regression analysis(regression method)is performed.The established regression model has statistical significance F(5,126)=34.568(p<0.05),adjust R2 = 0.578.The effects of the five independent variables included in the model on the change of the inclination angle of the mandibular third molar before and after treatment were statistically significant(p<0.05).The regression equation of the change of the inclination angle of the mandibular third molar(?M3-?FH)before and after treatment is: ?M3-? FH =20.623-0.150 × MP-SN(T1)-0.263 × ANB(T1)+0.043 × M3-?FH(T1)+3.550×RI(T1)+10.967× extraction 2.Multiple linear regression analysis(back-off method)was performed with RI ratio change(?RI)as the dependent variable.The established regression model had statistical significance F(4,127)=367.432(p<0.05),and adjusted R2=0.92.The four variables included in the model had statistically significant effects on the change of RI ratio before and after treatment(p<0.05).The regression equation for the change of RI ratio(?RI)before and after treatment is: ?RI =0.328-0.002×MP-SN(T1)-1.355×ANB(T1)-0.006×RI(T1)+0.345× extraction3.Multiple linear regression analysis(regression method)was performed with the tilt angle of the mandibular third molar(M3-?FH(T2))as the dependent variable.The regression model had statistical significance F(5,126)=215.004(p<0.05).),adjust R2=0.895.The five variables included in the model had statistically significant effects on the change of RI ratio before and after treatment(p<0.05).The regression equation for M3-?FH(T2)after correction is: M3-? FH(T2)=-18.217 +0.173×MP-SN(T1)+0.403×ANB(T1)+8.550×RI(T1)+0.916×M3-?FH(T1)-10.387× extractionconclusion:1.Mandibular plane angle,ANB angle,RI ratio and whether or not tooth extraction is the main factor affecting the change of the inclination angle of the mandibular third molar before and after orthodontic treatment.Before the correction,the angle of the mandibular plane and the larger the ANB angle,the smaller the change of the inclination angle of the mandibular third molar to the far middle erect;the larger the RI ratio,the larger the change of the inclination angle of the mandibular third molar to the far middle erect;the tooth extraction correction In patients,the amount of change in the inclination angle of the third molar of the mandible to the distal erect was larger than that of the non-extraction patient.2.Mandibular plane angle,ANB angle and tooth extraction are the main factors affecting the change of eruption gap of mandibular third molar before and after orthodontic treatment.Before the correction,the mandibular plane angle and the ANB angle were larger,and the change of the eruption gap of the mandibular third molar was smaller.The eruption gap of the mandibular third molar in the tooth extraction treatment was significantly increased compared with the non-extraction treatment.According to the mandibular plane angle,ANB angle,mandibular third molar angle,RI ratio and tooth extraction correction,the angle of inclination of the mandibular third molar can be predicted and evaluated.