Three-dimensional Finite Element Study On The Retraction Of Lower Anterior Teeth With Different Amounts And Locations Of Alveolar Bone Resorption

Objective:The increase in the proportion of adult orthodontic patients and the prevalence of periodontitis in adults has led to an increase in the number of orthodontic patients with periodontitis.25% of the alveolar bone resorption caused by periodontitis is localized.In order to clarify the orthodontic biomechanical changes caused by localized alveolar bone resorption,this paper uses three-dimensional finite element method to explore the difference in the initial displacement of teeth under different amounts and locations of alveolar bone resorption,and the role of microscrew anchorage under this condition,to clarify the changes in the position of the center of resistance of canines under different amounts and locations of alveolar bone resorption.Methods:Collect CBCT data(DCM format)from volunteers and import them into Mimics20.0 software,collect point cloud data,use Geomagic Studio automatic reverse engineering software to carry out surface fitting of point cloud data,and complete tooth and bone model construction.Use Solid Works to construct the absorbed alveolar bone model(absorbed to root 1/3;absorbed 1/2;labial absorbed 1/3 lingual absorbed 1/2;lingual absorbed 1/3 labial absorbed 1/2),teeth Peripheral membrane,bracket,arch wire model,and complete the assembly of each part.A load of 1.5N was applied in Ansys Workbench,and the anterior teeth were retracted by sliding method with and without miniscrew anchorage respectively.The position of the center of resistance of the canines in each group model was determined using the force line intersection method.The crown of each tooth,the maximum initial displacement of the root,the displacement in each axis,and the coordinates of the center of resistance of each group of canines were collected.Results:1.The anterior teeth showed different degrees of elongation,lingual inclination,and distal inclination in each group,and the anchorage molars mainly showed mesial inclination and lingual inclination,these movements increase as the alveolar bone resorbs.2.The total displacement of teeth increased with the increase of alveolar bone absorption,the total displacement of the two uneven absorption groups was less than the total displacement of alveolar bone resorption 1/2,and greater than alveolar bone resorption 1/2.The comparison between groups of heterogeneous absorption showed that there was a greater initial total displacement when the labial side was more absorbed than the lingual side.3.The application of microscrew anchorage significantly reduced the elongation of the anterior teeth,reduced the lingual inclination of the anterior teeth,prevented the mesial movement of the anchored molars and reduced the lingual inclination of the anterior molars.4.The center of resistance of the canines gradually moved to the root with the alveolar bone resorption.In the two groups with even alveolar bone resorption,the center of resistance of the canines shifted significantly lingually compared with the non-absorption group.In heterogeneous absorption,the center of resistance is shifted towards the side with less absorption.The total amount of change in the center of resistance is consistent with the change trend of the maximum initial displacement value.5.In all working conditions,the maximum stress of periodontal ligament is distributed on the labial and lingual side of the teeth,and the application of microscrew anchorage can slightly reduce the stress on periodontal ligament.Periodontal ligament stress increases with alveolar bone resorption.Conclusion:When the anterior teeth are retracted by the sliding method,for patients with alveolar bone resorption,the amount of alveolar bone wrapping the tooth root is the key.Patients with high total wrapping volumes always had smaller tilt and rotational displacements than patients with low total wrapping amounts.Under the same amount of wrapping,patients with more labial absorption of the alveolar bone will have more rotation and tilt.Microscrew anchorage is an effective method to reduce the inclination and rotation of the teeth when the anterior teeth are retracted by the sliding method.