Three-dimensional Finite Element Analysis Of Orthodontic Tooth Movement In Different Thickness Of Alveolar Bone

Objective :Three-dimensional finite element models with different alveolar bone thicknesses were established to simulate the application of orthodontic force on alveolar bone thickness.The stress-strain relation of maxillary central incisors,periodontal ligament（PDL）and alveolar bone in labial-lingual direction,distal direction,coronal direction and apical direction,and the impact of alveolar bone thickness of orthodontic tooth movement were compared to provide guidance for clinical practice.Methods :The morphology and alveolar bone thickness of the upper jaw incisors of a large number of oral outpatients were measured by cone beam CT（CBCT）,and three volunteers with high length and morphological similarity of the root of the incisors in the upper jaws and different thicknesses of the alveolar bones were selected.2.Through Mimics,Geomagic and other software,establish a three-dimensional model including teeth-periodontal membrane-alveolar bone,import the above data into the UG NX software finite element software in IGES format,simulate orthodontic clinics in the center point of the maxillary crown to assemble brackets on the built three-dimensional finite element model,and establish 3 orthodontic three-dimensional finite element models containing brackets,named model I,model II,model III,respectively.3.Simulated clinical loading of models I,model II,model III.maxillary incisors 100 g horizontal to distal,labial,lingual,and 50 g vertical extrusion and intrusion load,compared and analyzed the stress distribution of teeth,periodontal membranes and alveolar bone under the five stress systems of the three groups of models,and the initial displacement and displacement trend of teeth.Results:1.Three orthodontic three-dimensional finite element models of maxillary central incisor teeth with high morphological similarity and alveolar neck thickness of 6 mm,7.5 mm and 9 mm were established.2、The Von Mises stress distribution and maximum principal stress distribution of the teeth,periodontium and alveolar bone of model I,model II and model III showed that the maximum stress value was distributed at the crest of distal alveolar bone,and the maximum stress value gradually decreased with the increase of alveolar bone thickness,and the stress concentration area gradually decreased;The displacement trend showed that the orthodontic teeth moved in a distal trend with a little lingual trend,and the initial displacement of the tooth observation point gradually increased with the increase of the alveolar bone thickness3、The Von Mises stress distribution and the maximum principal stress distribution of the teeth,periodontium and alveolar bone in Models I,II and III showed that the maximum stress was concentrated at the alveolar crest on the labial side when a100 g load was applied to the maxillary central incisors in the labial direction.The maximum stress values of teeth,periodontium and alveolar bone showed a decreasing trend.The initial displacement trend showed that the orthodontic teeth moved in a labially inclined direction with a small amount of distal and apical trend,and the initial displacement of the tooth observation points gradually increased.4、The Von Mises stress distribution and the maximum principal stress distribution of the teeth,periodontium,and alveolar bone of Model I,Model II,and Model III showed that the maximum stress was concentrated at the lingual alveolar crest when a 100 g load was applied lingually to the maxillary central incisors.With the increase of alveolar bone thickness,the maximum stress values showed a decreasing trend.5、The Von Mises stress distribution of the teeth,periodontium,and alveolar bone in Models I,II,and III when an coronal load of 50 g was applied vertically to the maxillary central incisor showed that the stresses were concentrated at the top of the lingual alveolar crest and the root apical.The trend of the stress distribution was that the maximum stress value tended to decrease as the alveolar bone thickness increased;the displacement trend was that the extrusion movement was accompanied by a small tendency of lingual and proximal mesial inclination,and the initial displacement of the tooth observation point gradually increased.6、The Von Mises stress distribution of the teeth,periodontium and alveolar bone of Model I,Model II and Model III showed that the stresses were concentrated at the crest of the alveolar on the labial side and the apical part when a 50 g depression load was applied vertically to the maxillary central incisor.The trend of stress distribution was as follows: with the increase of alveolar bone thickness,the maximum stress value tended to decrease,and the stress concentration area gradually decreased;the orthodontic teeth showed the trend of depression movement with a small amount of labial and distal trend,and the initial displacement of the tooth observation point was gradually increased.Conclusion :1、When the teeth move in the distal,labiolingual,coronal and apical direction under the action of orthodontic force,the maximum stress of the teeth and periodontal ligament is concentrated in the tooth neck and apex,and the maximum stress value of the alveolar bone is distributed in the alveolar ridge.This further reveals the reason why the root and alveolar bone resorption of orthodontic clinics are mostly concentrated in these parts.2、The thicker the alveolar bone,the smaller the maximum stress value of the teeth,periodontal ligament,and alveolar bone;in clinical orthodontics,adverse reactions such as bone fenestration,dehiscence and root resorption mostly occur in patients with thin alveolar bone thickness.3、The thicker the Alveolar bone is,the easier the tooth moves,and the larger the initial displacement is.The thinner the alveolar bone,the more difficult the tooth moves,and the smaller the initial displacement is.4、With the popularization of CBCT,it is of great clinical significance to evaluate the thickness of Alveolar bone before orthodontic treatment.