Three Dimensional Finite Element Analysis Of The Anterior Teeth During Maxillary Dentition Distalization By Using Micro Screw Implant

ObjectiveDuring establishing a maxillary three-dimensional finite element model which contains maxillary dentition,periodontal ligament,cortical bone,cancellous bone,straight wire bracket,straight arch wire,anterior retraction hook(ARH),micro screw implant,the author studies on Initial variation of displacement trend of anterior teeth,the characteristics of stress distribution in periodontal ligament and the dangerous trend of root resorption,and the research results will provide a theoretical reference for the related problems encountered in the process of clinical orthodontic diagnosis and treatment.MethodThis study includes three experimental parts:Experiment 1(establishing a maxillary three-dimensional finite element model integral distal moved by micro screw implant): using the 256 row spiral CT to scan volunteer's maxillary in order to obtain CT medical images,through medical image processing software(Mimics),reverse engineering software(Geomagic Studio)to obtain the complete surface model,then assemble bracket,arch wire,hook,and micro screw implant by using Unigraphics NX software,and use ANSYS workbench software to establish a total of 12 complete models made up of different height of retraction hook(2mm,5mm,8mm,11mm)and different curvature of arch wire(10 degrees,15 degrees and 20 degrees).Finally,the boundary constraint,the material parameter setting and the grid partition are carried out to the entity model.Experiment 2(anterior teeth initial displacement trendency owing to different retraction hook height and curvature of rocking-chair arch wire): Based on model of experiment 1,on the codition of 3N in orthodontic retraction loading,by establishing 2-2 operation model to analyze The characteristics and changes of the instantaneous displacement tendency distribution of a single tooth.Experiment 3(Changes of periodontal ligament stress by different retraction hook height and different curvature of rocking-chair arch wire): on the basis of experiment 1,combined with the displacement tendency of experiment 2,analyze the distribution and changing regulation of the periodontal membrane equivalent stress(Von read Mises stress),the maximum principal stress(maximum tensile stress),and the minimum principal stress(maximum stress)in the meanwhile,explore relationship between root resorption and Periodontal stress.ResultIn Experiment 1,we successfully established a maxillary three-dimensional finite element models including maxillary dentition,periodontal ligament,cortical bone,cancellous bone,brackets,straight wire arch wire,retraction hook and micro screw implant,in the meanwhile the model has highly geometric similarity and mechanical similarity.In experiment two,we found that the use of retraction hook and rocking chair arch wire can make the anterior tooth's crown to move toward labial direction as well as complete tooth toward down direction,at the same time,the trend of displacement increases with the increase of both.In addition,the rocking-chair arch wire can also counteract the distal towards movement trend of the canine's crown due to the anterior teeth adduction.In experiment 3,it was found that the use of rocking chair arch wire and retraction hook all increased the equivalent stress of periodontal ligament,and the effect on the canine and lateral incisors was more obvious.The most easily absorbed area of root is located on the apex and neck of the root,in addition the lateral incisors and canines are located on the sides of the retraction hook,their periodontal stress is easily affected by the elastic deformation of the arch wire caused by the retraction hook.Conclusion1? By three-dimensional finite element analysis,the complex biomechanical problems in orthodontic diagnosis and treatment process can be transformed into specific figures,and the constructed model has high clinical similarity,and the results are true and reliable,providing powerful help for orthodontic research.2 ?The use of the rocking-chair arch wire and the retraction hook can prevent the adverse effect of the loss of the torque in incisor teeth during the overall movement of the maxillary teeth through the micro screw implant.3? Through the influence of retraction hook and rocking chair arch wire on the trend of tooth displacement,we can predict the concentration area of the equivalent stress of periodontal ligament and predict the location of root resorption easily,so as to provide guidance for clinical operation.