Three-dimensional Finite Element Analysis Of Clear Aligner In Maxillary Expansion

Objective:To evaluate the biomechanical effects of different designs of expansion way on the torque of maxillary posterior teeth with clear aligner by three-dimensional finite element analysis.To analyze the stress distribution and tooth displacement trend.The aim is to provide theoretical reference for clinical application when expanding maxillary with clear aligner.Method:A volunteer with individual normal occlusion was selected as the subject for this study.Spiral computed tomography was used to obtain digital models with the consent of the volunteer.A 3D finite element model was established by Unigraphics NX1911 and Geomagic Studio 2015 software,including maxillary teeth,maxillary bone,periodontal ligament（PDL）and clear aligner.The models were used to simulate the maxillary expansion with different torque.Four Configurations were designed to analyze the displacement trend and stress distribution of the maxillary posterior teeth by ANSYS workbench.Configuration 1:Expansion of posterior bodily by 0.2 mm;Configuration 2: Add a horizontal rectangular attachment（1*2*3mm）to the center of the posterior teeth clinical crown,expansion of posterior bodily by 0.2 mm;Configuration 3:An additional 0.5° of buccal root torque for upper molars and premolars,then 0.2 mm expansion;Configuration 4:An additional 1° of buccal root torque for upper molars and premolars,then 0.2 mm expansion.Result:1.When the maxillary arch is expanded by clear aligner,the equivalent stress of PDL in the canine teeth and premolar area is relatively large,mainly concentrated in the root tip and the tooth neck.The maximum equivalent stress of PDL was 9.37E-02 MPa in the first premolars under configuration 3.2.Under the four configurations,the posterior teeth area showed the displacement trend of buccal and distal。3.Under the loading of the four configurations,the sagittal shape is upward,and the posterior teeth all have a tendency to move distally and obliquely.The buccal displacement of the crown gradually decreased from the first premolars to the second molars,and the displacement difference of the crown root of the posterior crown was the minimum and the trend of overall movement was observed at configuration 4.Vertical upward,palatal tip sagging was shown in both working configuration 1 and2.A small amount of palatal tip intrusion was observed in the first molar at working configuration 3 and 4,and a small amount of intrusion was observed in the second molar at working configuration 4.Conclusion:1.The efficiency of expansion decreased from canine to first molar.2.There is no significant difference in the overall movement of the molar teeth with or without the design of the posterior attachment.3.When the maxillary arch is expanded by clear aligner,it will be accompanied by a distal tipping movement.4.Additional 10° buccal root torque for posterior teeth were improved with the objective of reducing excessive tipping of the teeth planned for maxillary expansion with clear aligner.5.It’s necessary to preset extra buccal root torque of posterior teeth according to initial torque,maxillary basal bone width,the position of teeth in the alveotor bone.