Analysis Of The Maxillary And Mandibular Alveolar Basal Arch Widths By Adjusting The Sagittal Position Of The First Molar

Objective: In clinical practice,the substance of using the plaster model to analyze the basal arch width is to measure the width of the alveolar corresponding to the sagittal position of the first molar.The difference of the width of the maxillary and mandible is 5mm as the standard value to evaluate whether there is transverse discrepancy.However,after orthodontic treatment,the sagittal position of the first molar often changes,and the corresponding width of the alveolar arch also changes.Therefore,the transverse analysis based on the first molar before orthodontic treatment actually has errors.Therefore,in this study,the sagittal position of the first molar was corrected by simulating the end target position after correction,and then the transverse analysis was carried out,in order to make the measurement and analysis results more accurate,which has more guiding significance for the clinical formulation of the treatment plan.Methods: 30 patients of Class II and Class III were selected to obtain their digital dental scanning files.Using 3 Shape software to reconstruct the initial digital model which is the uncorrected group T0;first,keeping the position of the first molar of the maxillary,moving the first molar of the mandible,making the first molar of both sides reach the neutral relationship,obtaining the model of the mandibular correction group T1;then,moving the first molar of the maxillary and mandible,making the first molar of both sides reach the neutral relationship,getting the bimaxillary correction group T2;last,keep the position of the first molar of mandibular,move the first molar of maxillary,making the first molar of both sides reach the neutral relationship,obtaining the model of the maxillary correction group T3;The width of four groups digital models were measured and analyzed by the center of alveolar crest analysis.The statistical analysis software spss22.0 was used to compare the difference of the four groups width analysis results by paired sample t test.At the same time,the linear correlation analysis was used to determine whether there was a linear correlation between the sagittal correction of the first molar and the change of transverse discrepancy.If there was a linear correlation between the two,a linear regression analysis is performed on the two to further quantify the correlation results.Results: 1.The measurement results of alveolar basal bone width at different sagittal positions of the bimaxillary first molars were different between the groups,and the difference was statistically significant(P <0.001).2.The width of the T0 group was larger than that of the T1,T2,and T3 groups in Class II patients,and the difference was statistically significant(P < 0.001).3.The width of the T0 group was smaller than that of the T1,T2,and T3 groups,in Class III patients,and the difference was statistically significant(P < 0.001).4.There was no statistically significant difference in the magnitude of the bimaxillary alveolar basal bone transverse discrepancy between T1,T2,and T3 groups in Class II and III patients(P> 0.05).5.There was a linear correlation between the sagittal correction of the first molar and the change of transverse discrepancy.Class II patients were negatively correlated with a correlation coefficient of-0.83 and regression coefficient was-0.32.The transverse discrepancy decreased by 0.32 mm averagely for every 1mm correction of the sagittal direction.Class III patients were positively correlated with a correlation coefficient of 0.938 and regression coefficient of 0.34.The transverse discrepancy increased by 0.34 mm averagely for every 1mm correction of the sagittal direction.Conclusions: 1.Correcting the sagittal position of the first molar by simulating the terminal target position and then performing transverse analysis can reduce the errors existing in the traditional transverse discrepancy analysis method and help to correctly design the treatment plan.2.For the same patient,the sagittal position of the first molar was corrected by different movements of the first molar,and the results of transverse analysis were consistent.3.There was a linear correlation between the sagittal correction of the first molar and the change of transverse discrepancy of maxillary and mandible alveolar arch.Class II is a negative linear correlation,Class III is a positive linear correlation.