Effects Of Insertion Angle Of Mini-implant On Mini-implant-assisted Rapid Palatal Expansion:A Finite Element Analysis

Objective:The purpose of this study was to compare the stress distribution and displacement on the craniofacial structures resulting from mini-implant-assisted rapid palatal expansion(MARPE)with different insertion angles using finite element analysis(FEA).The simulated findings might improve our understanding of the biomechanics of treatment modalities and be applied to the clinical protocols.Methods:The computed tomography(CT)scan images of a 20-year-old female were imported into Mimics 17.0 software to generate a three-dimensional(3D)model of the skull.The mid-palatal suture and all circumaxillary sutures were modeled with a width of approximately 1.5 mm,and the thickness of the periodontal ligament was set at 0.2 mm.The skeletal expander and mini-implants(MI)used in this study were constructed with SolidWorks software.The expander,MIs and the 3D skull model were imported into 3-matic software to generate a finite element volumetric mesh.Five finite element models were created to simulate different insertion angles of the MI anchorage:MIs inserted at 80°,85°towards the direction of expansion force,MI inserted at 90°,and MIs inserted at 85°,80°opposite the direction of expansion force.Then five models were imported into Abaqus software to perform FE simulations.Expanders were activated transversely by 0.5 mm,and the stress distribution and displacement of landmarks were evaluated for all models.Results:In all types,no significant difference was observed in the stress distribution patterns on the craniofacial complex.MI inserted at 80° opposite expansion force had more beneficial effects on skeletal expansion,primary stability and the decreased deformation of MI,but it had an extrusive tendency along the long axis of MI.MI inserted at 90° was more advantageous than other types in terms of dental tipping.MI inserted at 80° towards expansion force showed a more parallel expansion of maxillary halves in the coronal plane.Conclusions:In MARPE,insertion angle of MI was closely related to the stress distribution on the surface of MI and in the peri-implant bone,the effects of dental tipping and skeletal expansion,but it did not significantly affect the stress distribution patterns on the craniofacial complex.Based on our results,the insertion angle of 80° opposite force direction was recommended firstly for MARPE in terms of achieving orthopedic effects.The clinicians could consider the insertion angle of 80° opposite force direction as alternative to vertical insertion,on condition that the MIs were capable of resisting the extrusive tendency.