Three-dimensional Finite Element Analysis Of The Mesial Movement Of Mandibular First Molar With Clear Aligner

Objective: The clear aligner has obvious advantage in pushing the molars to move to far,but it is difficult to achieve the bodily movement of the molars in the extraction of the second premolars,during which the molars may be slanted.The application of clear aligner attachments and elastic traction can significantly improve the effectiveness of the appliance on tooth control,which is beneficial to the overall movement of teeth.Therefore,the study on the influence of different types of attachments and different traction methods on the mesial movement of molars has certain reference significance for clinical work.Methods: Part 1,a three-dimensional finite element model of mesial movement of mandibular first molars by clear aligner was established.Firstly,the image file of an adult female in individual normal occlusion obtained by CBCT scan was saved in DICOM format,and then imported into Mimics21.0 software.The mandible and mandibular teeth were separated,and the periodontal membrane was formed by Boolean operation to establish the initial model.The file of the initial model was imported into the Geomagic studio software in STL format,in which the clear aligner,attachments,power arm traction arm and other devices were created,and then assembled in soild works software to form the final model,which was saved in STL format.Part 2Influence of clear aligner on the mesial movement of molars under different attachment designs: The STL file of the final solid model was imported into Ansys software to simulate the displacement trend of mandibular first molars and the stress of periodontal membrane under different attachment designs during the mesial movement of mandibular first molars caused by clear aligner.Part 3: The influence of clear aligner on the mesial movement of molars under different traction design: The displacement trend of mandibular first molars and the stress of periodontal membrane under different traction design in the process of the mesial movement of mandibular first molars made by clear aligner.Results: Part 1: The 3D finite element model of mesial movement of mandibular first molars by clear aligner was established successfully.Part 2: In the process of making the mesial movement of the first molar with aligner,all the working groups in this experiment were mesial incline,lingual torsion and compression movement,but the double vertical rectangular attachment group had the bettert effect in controlling the overall mesial movement of the first molar.Part 3: In the process of the mesial movement of the first mandibular molars caused by the clear aligner,the mesial incline,lingual torsion and compression movement trends of all working groups in this part were smaller than those in the corresponding working groups in the second part of this experiment(the group without attachments and the 5*2*1 horizontal rectangular attachment group).Among them,5*2*1 horizontal rectangular attachment with power arm mesial class Ⅱ traction group has the best effect on mesial movement root control of molars.Conclusion:1.During the mesial movement of the mandibular first molar with clear aligner,mesial inclination,lingual torsion and compression of the molar will occur,but the attachment placed on the buccal side of the molar,mesial class Ⅱ traction,and the traction method of the Power arm can reduce these movement trends.2.During the mesial movement of the mandibular first molar with clear aligner,the root control effect of the buccal vertical rectangular attachment of the first molar of the same size is stronger than that of the horizontal rectangular attachment,and the longer the length of the horizontal rectangular attachment,the better the root control effect.3.Without traction,the double vertical rectangular attachment has the better root control effect during the mesial movement of the mandibular frist molar,and the molar is closer to the bodily movement.4.The group of 5*2*1mm horizontal rectangular attachment and mesial class Ⅱ traction with power arm can obtain the better root control effect.