The Clinical Evaluation Of Clear Aligners In Tooth Movements With First Premolar Extraction Treatment

Objective: To compare achieved and predicted tooth movements of maxillary teeth after first premolars extraction by measuring the digital three-dimensional model,and to provide guidance for clinical modification of the treatment scheme of the clear aligner.Methods: According to the inclusion exclusion criteria,20 cases were treated by extraction of first premolar with Invisalign,including 4 males and 16 females.The patients were randomly divided into group A(7 days)and group B(14 days)according to the time of appliance replacement.According to the different amount of permitted molar mesial movement,they were divided into three groups: C(? 0mm)D(0-2mm)E(> 2mm).Clincheck software was used to design the movement path of teeth,and digital models were made before treatment(T0)and after treatment(T1 is the achieved position of teeth,T2 is the predicted position of teeth).The 3D coordinate system was established in Geomagic studio 2012,and the best fitting and alignment were carried out.After that,the fixed points were made at the central incisor,canine and first molar respectively.The same operator repeated the measurement three times in the interval of one month,took the average value and recorded it.The data were imported into SPSS 22.0 software to calculate the buccolingual,mesial and distal,vertical movement distance,torque angle,axial inclination and rotation angle of the central incisor,canine and premolar.Results:(1)There are differences between the actual movement of the central incisor,canine and the first molar in buccolingual,mesial and distal,vertical movement as well as in the axial inclination angle,rotation angle and torque angle.(2)In the linear distance,the central incisor has the largest vertical difference,the difference is 0.38±0.92mm;the canine has the largest difference in the mesial and distal distance,the difference is 0.48±1.61mm;the first molar has the largest vertical difference,the difference is 0.54±1.71 mm.In terms of angle,the central incisor has the largest difference in torque angle,with a difference of 0.73±1.67°;the canine has the greatest difference in axial inclination angle,with a difference of 1.46±1.58°;the first molar has the largest difference in axial inclination angle,The value is 0.13±0.13°.(3)There was no significant difference between group A and group B(P > 0.05).(4)There was a significant difference among group C D and E(P < 0.05).Conclusions:(1)When the Invisalign were used for tooth extraction,there is a difference between the achieved and precited.When the clear aligner is used for extraction,the difference of the movement of the anterior teeth is the vertical movement,and the difference of the movement of the canine and the first molar is the largest in the axial inclination angle.The difference of movement is not related to the replacement time of the patient,but related to the permitted amount of molar mesial bodily movement.(2)In the treatment of extraction,the anterior teeth increase the over correction of intrusion,the canine increase the over correction of crown moving to mesial direction,and the molar increase the over correction of crown moving to the distal direction and extraction.