| ObjectiveTo construct a 3-D finite element model(FEM)of mandibular dentition distalization by micro-implant with the individual lingual appliance.Simulate clinical loading system by changing the position of micro-implants and the height of traction hooks,in order to analyze the biomechanical characteristics and stress of periodontal ligaments(PDL)both in mandibular dentition distalization and mandibular molars distalization by micro-implants with customized lingual appliance,and to provide references for clinical application.Methods3-D finite element models were established in section 1.An adult with individual normal occlusion was chosen as a volunteer.Spiral CT scanning was applied to the volunteer's mandibular.Then the data was imported into Mimics 17.0 software to get the 3D model.With the help of Geomagic Studio software,the 3D model of mandibular bone and dentition was obtained.The three-dimension models of individual lingual brackets,arch-wire,micro-implants,traction hooks and so on,were constructed by UG NX8.5 software.Meanwhile,all of the constructed models were assembled in Ansys software and defined.Finally,the 3-D FEM for individual lingual bracket system for distalizing the whole mandibular dentition was established.The changing regularity of the dentition displacement was studied in section 2,Three conditions were built on the three-dimensional finite element model.Condition 1,the micro-implants were located in the buccal shelf area between the mandibular first molar and the second molar.The angel of the micro-implants and occlusion plane was 70~80 degrees.The length of the traction hooks were 2mm,which were connected at the midpoint of the buccal segment wires between the canines and the first premolars.Condition 2,the micro-implant and the traction hooks were the same as condition 1,but the length the traction hooks was 8mm.Condition 3,the micro-implants were implanted in the posterior area of the second molars,which was perpendicular to the surface of the external oblique ridge of the leading edge of the mandibular ramus.The traction hooks were the same as condition 1.Loaded with 3N force between the top of the traction hooks and the neck of the micro-implants.To read and analyze the threedimensional initial displacement of the mandibular dentition and the equivalent stress distribution of periodontal ligaments.The changing regularity of the distalizing mandibular molar was studied in section 3.Two conditions were built on the three-dimensional finite element model.Condition 4,the micro-implants were the same as condition 3.The length of the traction hooks were 2 mm,which were connected at the buccal surface of the first molar,Loaded with 2.5N forces between the top of the traction hooks and the neck of the micro-implants.Condition 5,the micro-implant and the traction hooks were the same as condition 4,Loaded with 2.5N forces between the top of the traction hooks and the neck of the micro-implants.At the same time,Loaded a thrust of 1.25 N on the lingual side between the second premolars and the first molars.To observe the initial displacement and stress distribution of the mandibular first molars and second molars.ResultsIn section 1,the high precise three-dimensional finite element model was established,including customized lingual brackets,lingual arch wire,traction hooks,sectional arches,dentition,periodontal ligaments,alveolar bone and micro-implants.In section 2,in all of the three working conditions,there was a distalization trend of the mandibular dentition on the sagittal direction and a narrowing trend of the dental arch on the horizontal.In working condition 1,the occlusion plane showed a counterclockwise rotating trend,the molars drifted to the distal slantly with intrusion,the premolars extruded,and the canines drifted to the distal slantly,while the incisors showed a tendency of proclined and intrusion.In condition 2,the counterclockwise rotating trend of the occlusion plane declined,the molars and the canines tended to bodily distal movement,the intrusion trend of molars declined,the extrusion trend of premolars increased,while the proclined and intrusion tendency of the incisors increased.In condition 3,with the location changing of micro-implant,the occlusion plane showed a counterclockwise rotating trend,the molars drifted to the distal slantly with intrusion,while the premolars and anterior teeth tended to distalization movement with extrusion.In section 3,the first molars and second molars tended to distalization movement.In condition 4,both the first and second molars showed an obvious tendency of lingual rotation on the distal surface.In condition 5,the first molars tended to bodily displacement,while the second molars tended to slant movement.Conclusions1.A high precise and better geometrical similarity 3-D FEMs of mandibular dentition distalization by micro-implant with the individual lingual appliance was established,with the help of CT scanning and a series of software.To provide a stage for further biomechanical research during the distalization of mandibular dentition.2.During the mandibular dentition distalization with customized lingual system,forces loaded between the buccal traction hooks and the neck of the micro-implants.(1)When the positions of the micro-implants were fixed,with the length increased of the buccal traction hooks,the counterclockwise rotating trend of the occlusion plane declined,the posterior teeth trended to bodily movement,but the teeth beside the traction hooks showed an obvious tendency of rotation,and the narrowing trend of the dental arch increased.(2)When the positions and the length of traction hooks were fixed,with the positions changed of the micro-implants,the counterclockwise rotating trend of the occlusion plane increased,and the dental arch still showed a narrowing trend.(3)The counterclockwise rotating trend of the occlusion plane is beneficial to class III malocclusion patients,who are always with an high angle and a tendency of openbite.(4)Be attention to the rotation trend of the teeth beside the traction hooks and the narrowing trend of the dental arch,in order to take a comprehensive analysis on the three-dimensional change of the dentition.(5)Be attention that the magnitude of the traction force in individual lingual appliance should be smaller than in labial orthotherapy.3.When there is a crowding in the anterior or middle of mandibular dentition,or dental midline discrepancies,in order to avoid the to-and-fro movement of anterior teeth,we should push molars back first,then move the other teeth distalization.If we distalize the first and second molars at the same time,the traction force(250g)should be loaded on both the lingual and labial side,which is beneficial to the molars bodily movement.But the influence on teeth movement of different magnitude of the traction force loaded on lingual and labial side needs further studies.Also,we need to take some actions to resistance the counter-acting force on premolars.4.The teeth displacement in finite element analysis is immediate movement,which couldn't represent the clinical outcome.In clinical orthotherapy,teeth movement is influenced by many factors,such as periodontal tissue reconstruct,time of force loading,force attenuation,state of oral and maxillofacial muscles and function.And we will take actions avoiding the rotation?extrusion or intrusion trend of the teeth in clinical orthotherapy.Our study just take a briefly analysis on the biomechanical characteristics in mandibular dentition distalization by micro-implant with the customized lingual appliance,and for some other way of force loading in clinical orthotherapy,there needs further studies. |
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