Three-dimensional Finite Element Analysis Of Upright Movement Of Mandibular Mesial Inclined Second Molars

Objective : Through the establishment of three-dimensional finite element models of upright mandibular mesial inclined second molars with different orthodontic methods,the displacement trend and periodontal ligament stress distribution of the second molars were observed in order to provide reference for clinical treatment of mesial inclined second molars.Methods : A 21-year-old female volunteer was selected through clinical specialist examination.After obtaining informed consent,scan CBCT to collect original data,import Mimics to extract data,establish three-dimensional models of mandibular first premolars,second premolars,first molars and second molars in Geomagic Studio,and establish bracket,buccal tube,arch wire,and micro-implant models in NX,and integrate all models.Finally,Ansys was used to set material parameters,meshing,boundary,coordinate system and load conditions.A three-dimensional finite element model of upright mandibular mesial inclined second molars under nine working conditions was established.In the segmental arch group,from condition 1 to condition 3,the mandibular second molars were mesially tilted 30°,45° and 60° respectively,and 0.5N thrust was loaded between the first molars and the second molars.The micro-implant group was from condition 4 to condition 6,the mesial inclination of the mandibular second molar was 30°,45°and 60°,respectively.The micro-implant was implanted on the buccal side of the second premolar and the first molar,and 0.5N thrust was loaded.From condition 7to condition 9,the mandibular second molars were mesially tilted 30°,45°and60°respectively.The micro-implants were implanted distally in the mandibular second molars and loaded with 0.5N tension.The initial displacement trend and periodontal ligament stress distribution of upright mandibular mesial inclined second molars under nine working conditions were measured.Results:In the segmental arch group,only the periodontal ligament stress in condition 1was within the physiological limit.The periodontal ligament stress of the distal microimplant group was less than that of the mesial micro-implant group.The stress concentration of periodontal ligament in the cervical region was observed in all cases.With the increase of the mesial inclination angle of the second molar,the displacement of the segmental arch group increased gradually,and that of the micro-implant group decreased gradually.The sagittal displacement of the mesial micro-implant group was larger than that of the distal micro-implant group,with a tendency of mesial buccal torsion at the same time of upright;the vertical displacement of the distal micro-implant group was larger,with a tendency of distal lingual torsion at the same time of upright.Conclusion: When the mandibular second molar was mesially tilted 30°,the effect of upright molar with segmental arch combined with Ni Ti spring is better,and the stress of periodontal ligament is within the physiological limit.The distal microimplant has a better elongation effect on the mesial inclined second molar,and the mesial microimplant has a better distal displacement effect on the mesial inclined second molar.The most suitable orthodontic force for microimplant traction of mesially inclined second molars is0.5-0.8N.