| Objective To establish a three-dimensional finite element model of the maxillary complex,tooth,periodontal ligament,and non-bracket stealth appliance to simulate the removal of the maxillary first premolar and the anterior teeth adduction to closed tooth extraction gap.To analyze and compare the tooth stress distribution,initial displacement and periodontal ligament stress distribution during the process of retraction of anterior teeth with no scattered space and different scattered spaces in invisible orthodontic treatment without brackets.Provide theoretical reference for invisible orthodontic treatment of anterior teeth retraction cases.Methods Cone beam CT(CBCT)was used to scan the maxillofacial region of volunteers to obtain the original experimental data required for modeling.Itk-snap medical image processing software was used for three-dimensional reconstruction,Geomagic wrap 2015 reverse engineering software,materialise magics 21.0 software and ABAQUS/CAE 2020 finite element analysis software were used to establish four groups of different anterior teeth scattered space models:0mm,0.25mm,0.5mm and 1.0mm.and the stress distribution,initial displacement and periodontal ligament stress distribution characteristics on anterior retraction were observed.Results 1.Based on the CBCT data of volunteers,itk-snap medical image processing software for three-dimensional reconstruction,Geomagic wrap 2015 reverse engineering software,materialise magics 21.0 software and Abaqus/CAE 2020 finite element analysis software,the three-dimensional finite element models of maxilla,teeth,periodontal ligament and clear aligner were successfully constructed,which laid a good model foundation for the experiment.2.When simulating the sagittal displacement of anterior teeth with no scattered gap adduct and scattered gap adduction,The initial total displacement of retracted anterior teeth with scattered gaps is larger than that of retracted anterior teeth without scattered gaps,and the initial total displacement increases with the increase of scattered gaps.3.The displacement of the anterior teeth when the anterior teeth were adducted belonged to the tendency of lingual inclination and elongation.The maximum stress of the periodontal ligament is mainly concentrated in the cervical region and the apical region of the tooth.The absolute value of the ratio of the initial maximum displacement of the anterior crown apex to the root apex was used to measure the trend of tooth tilt movement,the trend of tilt movement was obtained:1.0mm group<0.5mm group<0mm group<0.25mm group.4.After the extraction of the bilateral maxillary first premolars,the anterior teeth tended to move mesially and the posterior teeth moved forward.Setting scattered gaps increases the adduction of anterior teeth while consuming more anchorage of posterior teeth,and the anterior displacement of posterior teeth is greater than that of the group without scattered gaps,which requires better anchorage control.Conclusion 1.The initial total displacement of anterior teeth increases with the increase of scattered gaps,suggesting that in clinical design,setting scattered gaps of anterior teeth can increase the adduction efficiency.2.When using clear aligner for adduction of upper anterior teeth,with the increase of scattered clearance,the trend of inclined movement decreases.For patients who need more anterior teeth adduction and thin bone on the labial side of the root,setting 1.0mm scattered space adduction can increase the amount of crown adduction and minimize the mesial movement of the root,which can prevent bone windowing and bone cracking,but the elongation of the anterior teeth is large and needs better vertical control.3.When using clear aligner for adduction of upper anterior teeth,setting anterior teeth scattered in the space can increase the adduction,but at the same time consume more posterior teeth anchorage,clinical anchorage control should be strengthened. |
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