The Three-dimensional Finite Element Analysis On Distal Movement Of Mandibular Molar By The Micro-impant

Objective: Mandibular molar distalization was an important method of orthodontictreatment.A group of dental anchorage was used to distalize molar. Micro-implantanchorage had also been applied to distalize mandibular molar.To establish athree-dimensional finite element model including dentition,periodontalligament,mandibular,standard MBT straight wire brackets,archwire and micro-implantin this study.To analysis the stress and initial displacement when micro-implant indifferent locations,in different ways and in different tooth extraction healing distalizingmandibular molar.To explore the appropriate way of mandibular molar distalization,providing biomechanical basis for distalize mandibular molars in clinic.Method:1. A complete dentition and healthy young women volunteer was chosed byhead spiral CT scanning.Using the finite element modeling software to establish thefinite element model containing dentition,periodontal ligament,mandibular,standardMBT straight wire brackets,archwire and micro-implant.2. Three conditions were builton the three-dimensional finite element model.Ni-Ti spring was placed directly betweenmandibular first and second molar on condition one, loaded150g to distalizemandibular second molar. Condition two was based on condition one with incisor tofirst molar integral tied; Condition three was based on condition one with micro implantand first molar connected,micro implant was planted between first and second molar. Toobserve the stress distribution and initial displacement3. Micro-implant was plantedbetween mandibular second premolar and first molar, with micro-implant and secondpremolar connected. Ni-Ti spring was setted to distalize mandibular fist molar and second molar, loaded150g,200g,250g,300g force;4.Micro-implants were planted inthe bilateral second molar distal buccal directly with Ni-Ti spring stretching the hookbetween the lateral incisor and canine, loaded200g,300g,400g force.To observe thestress distribution and initial displacement5.Micro-implants were planted in thebilateral second molar distal buccal,pulling away directly the entire mandibularteeth.The third molar extraction socket was setted in the far side of the secondmolar,simulated granulation tissue, connective tissue, immature bone tissue and maturebone tissue.To observe the stress distribution and initial displacement on the differenthealing of tooth extraction.Results:1.A high precise three-dimensional finite element model wasestablished,including dentition, periodontal ligament, mandibular, standard MBTstraight wire brackets, arch wire and micro-implant.2.The periodontal ligamentmaximum Von-mises stress values were24.03kPa,24.03kPa,23.75kPa on threeconditions, below maximum stress level26kPa; The periodontal ligament Von-misesstress, teeth Von-mises stress and displacement values of anchorage teeth were smalleron condition two than on condition one, but very close. The displacement values ofsecond molar increased.The periodontal ligament maximum Von-mises stress values ofmandibular first molar increased with the increase in tilting trend.The periodontalligament Von-mises stress values and initial displacement values of the other teeth weresignificantly reduced on condition three than condition one.3.With the increase of thevalue of the loading force, periodontal ligament Von-mises stress values showed agradual upward trend.When loaded300g,the periodontal ligament maximum Von-misesstress of second premolar and first molar values were27.85kPa,28.01kPa, which weremore than26kPa; When loaded250g, the values were23.21kPa,23.34kPa, which werenot exceeding26kPa;5.When loaded400g, the periodontal membrane maximumVon-mises stress values of lateral incisor and canine were27.50kPa,20.67kPa, the value of lateral incisor was more than26kPa; when loaded300g, the values were20.62kPa,15.50kPa,which were not exceeding26kPa. Mandibular second molar was distalized by150g, distal inclination with lingual rotation; mandibular first and second molars weredistalized by250g, distal inclination. The first molar was much closer to the overallshift and the second molar distal tipping tendency decreased when mandibular dentitionwere pulled by300g. The maximum initial displacement values of micro implant inthese conditons were0.27um,0.35um and0.46um, micro implant bone interfacetricortical maximum Von-mises stress values were3.41GPa,6.07GPa and14.69GPa.5.Distalizing mandibular dentition in different extraction healing period, periodontalmembrane Von-mises stress values were lower than26kPa. Early tooth movementdisplacement increased, the maximum initial displacement of molar increased greatly.Conclusion:1.When mandibular second molar was distalized, the overall ligation ofanchorage teeth was failed to significantly enhance anchorage, micro-implant indirectanchorage could enhance anchorage, but anchorage teeth still moved mesially.2.Theappropriate force value of mandibular molar distalization was250g.3.The appropriateforce value of the entire mandibular teeth distalization was300g.4.Distal movement ofa group conducived to the overall molar movement and could shorten the treatmenttime,compared with individually molar movement.5.To distalize mandibular in theearly healing of tooth extraction teeth can be considered.