Effects Of Maxillary Expansion On Different Palatal Morphology:A Finite Element Analysis

Background:Some common problems exist and require maxillary expansion treatment in clinic orthodontic,such as underdevelopment of maxillary width and high-narrow palate.RME and MSE are usual measures that applied to correct arch constrict.Through clinical observation of patients need rapid maxillary expansions,we found that the palatal shapes of different patients are quite different,which has an impact on the placement position of expansion appliance,especially the height of expansion screw.In addition,the effects of arch expansion of patients with different palatal shapes in clinical are different.At present,researches have shown that the effects of maxillary expansion are affected by the timing of the expansion,the expansion method,the position and rigidity of the expansion device,but there are few relevant biomechanics studies focusing on the influence of palate shapes.The mechanical distribution of the craniomaxillary complex,the expansion effect and the selection and design of the arch expander for patients with different palatal shapes remain to be studied.Three-dimensional finite element analysis is an effective method to study the stress distribution and displacement trend,which has been widely used in the investigations of maxillary expansion.Therefore,this study further analyzes the expansion effects of RME and MSE under different palatal shapes using the three-dimensional finite element method.Objective:The aim of this study is to compare and analyze the biomechanical effect and the displacement trend of RME and MSE expansion on the maxillofacial complex under different palatal shapes by using finite element analysis,which provides foundation for choosing expansion treatment methods and designing the therapeutic regimen in orthodontic clinic.Methods:The three-dimensional model was obtained from a computed tomography image of a person with normal palate in MIMICS 20.0.The reconstructed model was exported to 3-matic Research 12.0 where sutures were built.Then,3D entity model was established in Geomagic Studio 2014 where noise was removed from the geometry and some contours were smoothed.After obtaining the CAD model of the maxillary complex,we modified the shape of the palate to obtain the three-dimensional CAD model with the high vault.Additionally,two expander devices were considered.MSE and RME were created and all models were assembled in ANSYS Workbench 19.0.Mesh was generated and material property boundary condition was set afterwards,and then lateral forced displacement were applied and the analysis results were obtained.Results:1.Four experimental models are finally established in this research.Model one is normal palate+RME,the number of elements is 364319,the number of nodes is 604354.Model two is normal palate+MSE,the number of elements is 379122,the number of nodes is 625033.Model three is high palate+RME,the number of elements is 248379,the number of nodes is 391358.Model four is high palate+MSE,the number of units is 249077,the number of nodes is 393106.They have excellent geometric accuracy and biological similarity,and their mesh quality,material properties and the contact relationship are rational.2.Stress distribution of the craniomaxillofacial complex:Compared with model 1,there is a larger stress concentration in the upper structure of the craniomaxillary complex in model 3,including the maxillary frontal process,the medial orbital wall and the orbital floor.The stresses of model 2 and model 4 are concentrated around the implants,and the stress on anchorage teeth and alveolar bone is smaller than that of model 1 and model 3.3.Stress distribution of the sutures:The stress of the mid-palatine suture and pterygopalatine suture during MSE expansion is significantly greater than that of RME expansion,while the stress is concentrated on the front sutures of the craniomaxillary complex during RME expansion,including the nasofrontal suture and mid-palatine suture.4.Comparison of maxillary expansion effects:Mid-palatine suture in RME expansion is widened in a V-shape,while that in the MSE expansion is evenly expanded.The lateral displacement of the palatal suture of model 3 is greater than that of model 1,and the maxilla has more rotation.The crown/root ratio of model 1 is significantly greater than that of the other three groups.The crown/root ratio of MSE expansion is lower than that of RME expansion,and the vertical control of the dentition is better.Conclusion:1.The stress distribution and the expansion effect of the cranio-maxillary complex will be affected by the shape of the palate when using RME.It is found that the maxillary frontal process and the medial orbital wall have obvious stress concentration in the high palate group and the lateral displacements of the mid-palatine suture and dentitions are larger than the normal palate group,but the shape of the palate has little effect on the expansion effects of MSE.2.The lateral displacement of the mid-palatine suture and dentition in MSE expansion is greater than that in RME expansion,and the mid-palatine suture is evenly expanded.MSE may achieve more effective maxillary expansion by overcoming the resistance of the palatine suture and pterygopalatine suture.Palatine suture in RME expansion is widened in a V-shape.3.The crown/root ratio of maxillary expansion using RME under normal palate is significantly greater than that of the other three groups,so it is more prone to tipping movement of the anchor teeth.The crown/root ratio in the MSE group is smaller than that in the RME group,suggesting MSE can effectively reduce the tipping movement and the stress concentration on the anchored teeth and the surrounding alveolar bone,managing the vertical control well.