Three Dimensional Finite Element Analysis Of The Upper Dentition Retraction With Micro-implant Anchorage

Stable and effective anchorage is crucial to successful orthodontic treatment.The “anchor” is a subject which resists the orthodontic or orthopedic loadingforces. There are many ways to strengthen the anchorage, such as facebow,Nance bow, TPA and so on. However, these devices have limitations in clinicaluse. The appearance of micro-implant anchorage provides effective ways toslove the problem.The micro-implant anchorage, as a stable anchorage, has many advantages,such as little trauma, easy operation, various implantation and immediateloading. Micro-implant anchorage could control mesial-distal movement,vertical movement and horizontal movement effectively. At present, theapplication of micro-implant anchorage consists of retracting anterior teeth,intruding anterior teeth, intruding posterior teeth, molar distalization andretracting the whole dentition in clinic.The whole dentition retraction with micro-implant anchorage is a newtechnology in clinical application, which is suitable for two kinds of patients:1. The non-extraction and mild maxillary protrusion case.2. Maxillary protrusionstill exists after extraction. The technology can not only correct the molarrelationship but also the maxillary protrusion. Nevertheless, there are some sideeffects in the treatment by the technology, such as the loss torque in anteriorteeth and openbite in molar area. In order to solve the problem, the orthodontiststry to change the height of hook and the curve of arch wire. However, how thesefactors affect the maxillary dentition has not been fully clarified.The three dimensional finite element method, as an effective theoreticalmethod in stress analyzing, has been widely used in biomechanical study. In ourstudy, we constructed the finite element models of maxillary dentition retractionwith micro-implant anchorage, and the stress distribution and mobile trend ofmaxillary were analyzed in order to provide biomechanical reference for clinicalapplication.The study is composed of three experiments as follows:Experiment1: The construction of3D finite element model. Objectives: Toprovide operation platform for following experiments through constructing3Dfinite element models including the upper dentition, alveolar bone, bracket, archwires and micro-implant. Methods: A23-year old female volunteer withindividual normal occlusion was scanned from occlusal plane to zygomatic archby CT after alignment and leveling. Import the CT date into Mimics8.1tocalculate3D models of the upper dentition and alveolar bone. After smoothingand substantiating the models with Catia software, the CAD model of the upperdentition and alveolar bone was constructed. The software Solidworks wasused to contribute periodontal ligament, brackets, arch wires and micro-implant.Assemble all parts of models in3D finite element models using AnsysWorkbench12.1software. Results: Finite element models of maxillary dentition retraction with micro-implant anchorage were constructed. Conclusion: On thebasis of CT data, it was feasible to construct high-quality3D finite elementmodel through general application of Mimics，Catia，Solidworks and Ansys.Experiment2: Finite element analysis of the effect of the upper dentitionretraction used different height of anterior retraction hook. Objectives: Toinvestigate the biomechanical effects of micro-implant anchorage on en-masseretraction of the maxillary dentition with different retraction hook heights.Methods: The forces and the initial tooth displacements were calculated whenthe restraction hook heights were1,4,7,10mm under the load of3Nrespectively on the basis of3D finite element model. Results: With retractionhook height increasing, the sagittal force increased, while the vertical forcedecreased gradually. The whole upper dentition will rotate from clockwise tocounter-clockwise. Conclusion:1. The upper dentition movement could bechanged effectively by different retraction hook heights.2. The center ofresistance of maxillary dentition was located9to12mm above the occlusalplane.Experiment3: Finite element analysis of the effect of the upper dentitionretraction used different curve of archwires. Objectives: To investigate thebiomechanical effects of micro-implant anchorage on en-masse retraction of themaxillary dentition with different curve of archwires. Methods: The mobiletrends were calculated when the curve of archwires were5,10,15degree underthe load of3N respectively on the basis of3D finite element model. Results:1.With the curve of archwire increasing, the labial torque of the centralincisor,canine and first molar increased gradually, the intruding effect of centralincisor and canine inceased, the intruding effect of the first molar decreasedgradually.2. With the archwire curve increasing, the counter-clockwise trend of the upper dentition rotation increased. Conclusion:1. The upper dentitionmovement could be changed effectively by different curve of archwires.2. Thecurve of archwire is10degree suitable for retracting the upper dentition withmicro-implant anchorage.