Three Dimensional Finite Element Analysis Of Maxillary Anterior Teeth Retraction With Micro-implant Anchorage And Sliding Mechanics Based On Hyperelastic Model Of Periodontal Ligament

Objective To explore the construction method of periodontal ligament hyperelastic constitutive model,and a more accurate and higher simulation three-dimensional finite element model of maxilla composed of maxillary teeth,alveolar bone,periodontal ligament,micro-implant,hook,wire,brackets is constructed to investigate the biomechanical effects of micro-implant anchorage technique with sliding mechanics on maxillary anterior teeth retraction under different implant insertion heights and sagittal positions between one-step and two-step methods.Methods One patient with maxillary protrusion was chosen from the CBCT database of Qingdao Stomatological Hospital.A three-dimensional finite element model of maxilla composed of maxillary teeth,alveolar bone,periodontal ligament,micro-implant,hooks,wire,brackets was constructed using Mimics Medical 17.0,Geomagic Studio 2013,Unigraphics NX 10,Solid Works softwares.According to the database of periodontal ligament tensile experiment from the literature[1],the stress-strain curve was generated using Ansys software,which stated the relations between Young’s modulus of the periodontal ligament and the load.Ansys finite element analysis software was used to simulate the sliding mechanics by loading 1.47 N force on traction hooks with different implant insertion heights(4,6 and 8mm,respectively)and sagittal positions(between the second premolar and the first molar,and between the first molar and the second molar)in order to compare the initial displacement between six maxillary anterior teeth(one-step method)and four maxillary anterior teeth(two-step method).Results 1.Using the same method to maxillary anterior teeth retraction,with the same sagittal positions of the micro-implant and the increasement of the micro-implant insertion heights,the initial displacement of maxillary anterior teeth retraction decreased and the initial displacement of maxillary anterior teeth intrusion increased.2.Using the same method to maxillary anterior teeth retraction,with the same micro-implant insertion heights and moving the micro-implant backward,the initial displacement of maxillary anterior teeth retraction increased and the initial displacement of maxillary anterior teeth intrusion decreased.3.With the same sagittal positions and insertion heights of the micro-implant,two-step method could produce more initial displacement of maxillary anterior teeth retraction and intrusion than one-step method.Conclusions 1.The construction method of three-dimensional finite element model of maxilla based on the periodontal ligament hyperelastic constitutive model has feasibility.2.The ideal teeth movement control could be achieved by different insertion heights of micro-implant and different sagittal positions of the micro-implant,and different insertion heights influence mainly the initial displacement of maxillary anterior teeth retraction,different sagittal positions the initial displacement of maxillary anterior teeth intrusion.3.Two-step method could produce more initial displacement than one-step method.