A 3-D Finite Element Study Of Mandibular Anterior Teeth Retraction By Using Micro-implant With Customized Lingual Appliance

ObjectiveTo establish three-dimensional(3-D)finite element models(FEMs)included mandible,dentition without the first premolars,periodontal ligament(PDL),customized lingual appliance,micro-implants,traction hooks,et cetera.The main purpose was to analyze the biomechanical characteristics when retracting mandibular anterior teeth by using customized lingual appliances to provide clinical application with a reference.MethodsThe 3-D FEMs needed were constructed in section 1.64-row Spiral computed tomography scanning was applied to obtain the data of the volunteer’s mandible.Then use the Mimics 20.0 software to get the geometric model of mandible and dentition without the first premolars.With the help of Geomagic Studio 2014 software,the geometric model was optimized and the model of periodontal ligament was obtained.The models of individual lingual brackets,arch-wire,micro-implants,traction hooks,et cetera were established by Unigraphics NX 10.0 software.The integral 3-D FEMs were established after setting material properties and FEM boundary and dividing FEM mesh by Ansys Workbench 18.2 software.Both the changing regularity of dentition displacement and the stress distribution on the periodontal ligaments were analyzed in section 2.Three different conditions were set up on the 3-D FEMs respectly.Condition 1,The Force of 1.5 N was loaded at the lingual side between the canine and the second molar.Condition 2,The Force of 0.5 N was loaded at the lingual side between canine and the second molar,and The Force of 1.0 N was loaded at the buccal side between canine and the micro-implant.Condition 3,the force that loaded both at the lingual side and the buccal side were same as the condition 2,but indirect anchorage was set up between the micro-implant and the second molar.Both the changing regularity of dentition displacement and stress distribution on the periodontal ligaments were also analyzed in section 3.Similarly,three different loading conditions were set up on the 3-D FEMs.In all of the three conditions,The Force of 0.5N was loaded at the lingual side between the canine and the second molar,and The Force of 1.0 N was loaded at the buccal side between the micro-implant and the given traction hook on the canine.From Condition 1 to 3,the length of the traction hook was 5mm,8mm,11 mm respectively.ResultsIn section 1,four different 3-D FEMs including mandible,dentition,periodontal ligament,customized lingual appliance,micro-implants,traction hooks,et cetera were successfully established.In section 2,the lingual tipping of anterior teeth,mesial tipping of the second premolar and molars and rotation tendencies of molars were observed when the force was loaded at lingual side only.Meanwhile the PDL Von Mises Stress of the canine and molars was far beyond the recommended range.When the forces were simultaneously loaded at both buccal side and lingual side,the lingual tipping of incisors reduced,the PDL Von Mises Stress of lower teeth was basically acceptable,and the distal tipping of canine raised.The appliances of micro-implant and indirect anchorage strengthened the molar anchorage,especially in reducing the rotation tendencies of molars.But it may also lead to a few mechanical side effects.In section 3,as the length of the labial traction hook increased,the lingual tipping of incisors reduced obviously,but the distal tipping of the canine reduced a little.Most teeth’s PDL Von Mises Stress of Most teeth was acceptable,except that the canine’s was slightly beyond the recommended range.No bodily retraction of incisors was observed when the length of traction hook was 11 mm.ConclusionsThe 3-D FEMs of mandibular anterior teeth lingual retraction force system were constructed with good similarity in geometric and mechanical aspect and could be used for the further research of biomechanics for the lingual orthodontics.The mandibular anterior teeth lingual retraction force system which combined with the buccal force and traction hook could reduce the lingual tipping of anterior teeth,which is conducive to root control movement of anterior teeth.But the labial traction hook had a limited influence on reducing the distal tipping of the canine.The appliances of micro-implant and indirect anchorage strengthened the molar anchorage,especially in reducing the rotation tendencies of molars.