Three-dimensional Finite Element Analysis Of Mandibular Molar Movement Pushed By Bracketless Invisible Appliances

Objective:To study how anchorage allocation and difference in moving distance influence the stress distribution and displacement variation tendencies of mandibular anteriors when invisible appliances push mandibular molars backwards,and offer references to orthodontists concerning anchorage allocation and treatment planing using invisible appliances to push mandibular molars bodily backwards.Methods:1.A finite element analysis model of maxillary and mandibular dentition,pericementum,mandible and maxilla,and mandibular invisible appliances: The experimental subject should be a female individual normal adult volunteer,healthy,without systematical or oral disease,whose wisdom teeth have been extracted for more than three months.The original experimental comes from the volunteer’s CBCT scan results.Modeling softwares including Mimics,Geomagic,Solid Works should be applied to creat the three-dimensional finite element model of maxillary bilateral first and second molar,full mandibular dentition and its supporting tissues,mandible and maxilla and mandibular invisible appliance.2.Three-dimensional finite element analysis of how anchorage and moving distance differences influence bracketless invisible appliances’ pushing mandibular molars backwards:By meshing and load setting the solid model from Experiment 1applying ANSYS three-dimensional finite element analysis software,the visual highprecision three-dimensional entity’s visual finite element three-dimensional model of mandibular molar backward pushed by invisible appliances under the condition of different anchorage was achieved.Modeling invisible appliances pushing first and second mandibular molars backwards.There are three large groups with moving distance measuring 0.15 mm,0.2mm and 0.3mm respectively.Every large group will be divided into for teams whose intramaxillary anchorage is mandibular 1-5 alone without traction;mandibular 1-5 combine with tractive force 2N,Type Ⅲ;mandibular 1-5,combined with microimplant anchorage with a height of 6mm between mandibular 6,7,loading tractive force 2N;mandibular 1-5,combined with micro-implant anchorage with a height of 6mm between maxillary 6,7,loading tractive force 2N.Observe and analyze the stress distribution of pericementum of the lower anterior teeth and the displacement tendencies of mandibular premolar.Results:1.Three-dimensional finite element analysis model of 16,26,17,27,14 mandibular teeth and pericementum,mandible and maxilla and mandibular invisible appliances.2.During the distalization of mandibular molars,slightly mesial and labial tipping movement will occur in anterior region no matter under what kind of anchorage allocation,while the amount of labial movement exceeds that of mesial movement.The movement amount and the stress born by pericementum of mandibular central incisors are largest,followed by that of lateral incisor,that of canine teeth the least.3.Assisted by Type Three traction and the microimplant anchorage of mandible and maxilla,adding anchorage in anterior region can effectively eliminate the mesial and labial tipping movement of mandibular anterior teeth and reduce the loss of anchorage in anterior region,among which the method joined with mandibular anchorage implant is the most powerful in reducing the mesial and labial tipping movement in mandibular anterior region.4.When mandibular molars move backwards,mandibular anterior region will be slightly pressed no matter under the condition of what kind of anchorage allocation,among which,it will be pressed to the lowest when joined with mandibular anchorage implant,the press influence will be the least when joined with maxillary anchorage implant.5.When mandibular molars move backwards,with movement distance increasing,the amount of mesial and labial tipping movement in mandibular anterior region will also increase,which will add the risk of anchorage loss of mandibular anterior teeth.Conclusion:1.The three-dimensional finite element model of mandibular invisible appliances pushing molars backwards established in this experiment accords closely with the real condition of organs of human oral cavity,which will provide relatively real and credible foundation of visual three-dimensional entity model for later experimental analysis and study.2.There will be slight anchorage loss in mandibular anterior teeth no matter what kind of anchorage allocation is applied when bracketless invisible appliances push mandibular molars backwards.3.Anchorage loss of mandibular anterior teeth will be effectively prevented when joined with Type Three traction and mandibular and maxillary microimplant,the effect of mandibular anchorage implant added will be the strongest.4.Mandibular anterior teeth will be pressed to some extent when mandibular invisible appliances push first and second molars backwards,the effect will be the strongest when joined with mandibular anchorage implant,which is suitable for patients with overbite.The effect will be slighter when joined with Type Three traction and maxillary anchorage implant,which patients with openbite can consider.5.When invisible appliances push mandibular molars backwards,with the increasing of the step distance of the appliances,the anchorage loss of mandibular anterior teeth will also increase.To ensure the effect of pushing molars backwards,reducing step distance can be considered on the situations that anchorage microimplant are not effective and Type Three traction can not be associated.