Transparent Aligners In Extractive Case With Different Approaches Anterior Retraction:three-dimensional Finite Element Analysis

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 frontal teeth adduction to closed tooth extraction gap.In transparent aligners appliance,the initial displacement and initial displacement tendency of the teeth during step-by-step adduction of the anterior teeth and the En-masse retraction movement of the anterior teeth,and the loading pressure points in the step-by-step adduction and En-masse retraction movement of the teeth were compared and analyzed.To provide theoretical basis for the orthodontic treatment of tooth extraction cases transparent aligners treatment in the adduction process of the teeth movement,for the clinical orthodontists in the extraction of teeth of frontal teeth adduction to provide a theoretical guidance.Methods: Cone-beam computed tomography(CBCT)scans the volunteers' head area to obtain experimental raw data.Mimics software,Geomagic Studio software,and Abaqus/CAE software were used to establish transparent aligner,highly similarly case in which the first premolar was extracted.Three-dimensional finite element model of transparent orthodontic correction,Sagittal loading 1N to adduction tooth,in the first step inward movement of caine and then anterior incisor,and En-masse retraction movement,and simulation of power ridge anterior teeth in adduction.set during each step of the anterior teeth movement sagittal loading 1N adduction Force and 1N root force couples to adduction tooth were used to measure the displacement of the left anterior teeth.The results were compared between the step-adduction of the anterior teeth and En-masse retraction movement on the stress distribution of the anterior teeth,and the stress distribution and initial displacement of the internal adduction of the anterior teeth.set during each step of the anterior teeth movement.Results:1.By scanning volunteer CBCT data,using mimics software for three-dimensional reconstruction,Geomagic Studio reverse engineering software and Abaqus/CAE finite elementanalysis software assisted modeling,successfully constructed the maxillary complex,teeth,periodontal ligament and The three-dimensional finite element model of the bracket-free invisible appliance has good similarity and reasonable mesh division,which lays a good model foundation for the experiment.2.In the step-by-step simulation and the En-masse retraction of the loading force in the sagittal direction,the initial displacement of the anterior teeth appears in the sagittal direction,and the initial displacement of the anterior teeth in the step-by-step and En-masse retraction is approximately the same.3.Step-by-step and En-masse retraction entire anterior teeth control of the unloaded pressure point.The displacement of the anterior teeth in the sagittal direction is uncontrollable.The stress distribution of the teeth is concentrated in the middle-upper 1/3 of the root.Periodontal membrane stress concentrated in the cervical and apical area.The front teeth in the vertical direction show a tendency of elongation.4.The step-by-step and En-masse retraction teeth of the loaded pressure point for control root show that the tooth movement tendency is both the lingual displacement trend of the root and the crown,and the displacement of the crown is greater than the displacement of the root,showing the slope of root control.Movement,tooth and periodontal membrane stress distribution is more uniform.The stress distributions of the teeth and periodontal ligament were uniform,and no obvious stress concentration area appeared.The initial displacement of the tooth was significantly reduced compared to the unloaded pressure point and the anterior tooth adduction,and was reduced more than50%.Conclusions: 1.When step-by-step and En-masse retraction of the anterior incisor are performed,the initial displacement of the anterior teeth in the sagittal direction is approximately the same,When prompted for clinical design,step or overall movement should be designed based on the condition of the anchorage.2.Step-by-step and En-masse retraction without pressure point control root of anterior teeth.The displacement of the anterior teeth in the sagittal direction is an uncontrollable lingual tilt movement,indicating that no bracket invisible appliance is adducted in the anterior teeth.Crown torque loss can easily occur.In the vertical direction,the anterior teeth showed a tendency of elongation,accompanied by a deepening of the covering.3.The step-by-step and En-masse retraction loading of the pressure point control root and the adduction of the entire anterior teeth were both tongue-directional displacements of the crown and the root,and the distal movement of the canine was trending,but the displacement of the crown was more greater than the displacement of the root.Compared with the step-by-step and En-masseretraction frontal adduction of unloaded pressure points,the initial displacement of the tooth was significantly reduced more than 50%,It is suggesting that the invisible appliance should be added as needed during the adduction of the anterior teeth,Root tongue torque is necessary,while reducing the amount of movement of each step of the appliance design.