Effect Of Three Types Of Rapid Maxillary Expansion:A Three-Dimensional Finite Element Study

Objective: By establishing a three-dimensional finite element model of maxillary complex and rapid maxillary expanders,comparing the transverse displacement,stress distribution and variation trends of tooth,alveolar bone and mid-palatal suture on three kinds of rapid maxillary expansion methods.To provide further biomechanical explanation for rapid maxillary expansion process,and provide the theoretical guidance for orthodontic clinicians about choosing and using rapid palatal expanders.Methods: DICOM image data of a volunteer’s head was obtained through CBCT.Forming a high similar maxillary complex’s three-dimensional finite element model by Mimics,Geomagic Studio,ANSYS Workbench software,and establishing the models of Hyrax,Haas and MARPE.Assembling the models and loading by 0.25 mm lateral forced displacement on the left and right coil springs of the expanders.Observing and analyzing the first premolars and first molars’ transverse displacement,total displacement and Von-mises equivalent stress;the mid-palatal suture’s increase of transverse width and change of maximum principal stress;maxilla’s lateral deformation,maximum principal stress,Von-mises equivalent stress and overall change tendencies;implant’s Von-mises equivalent stress.Results: Three kinds of expansion methods could expand mid-palatal suture and maxilla,also could cause the anchorage tooth of buccal inclination.Hyrax expander’s expansion effect was poor,the buccal inclination was obvious,maxilla was wedge-shaped open and had a clockwise rotation trend.Haas expander had better effect,its stress distribution was uniform and the maxillary changing tendency was mainly forward.MARPE brought the most significantly tooth horizontal displacement.The maximum value of the stress appeared in the middle of mid-palatal suture and the strain was the most significant,the maxilla has a counterclockwise rotation changing tendency.The maximum stress of MARPE was located in the jointing area of the implants and coil springs,adjacent bone tissue also had high stress,which spread around and decreased gradually.Conclusion: There were significant differences among the effect of three types of rapid maxillary expansion method.MARPE had the most significant changes in tooth and bone,and Haas expander had some advantages compared with Hyrax expander.