Explore The Factors Influencing The Stability Of Canine With Clear Aligners And Class Ⅱ Elastics:a Finite Element Analysis

ObjectiveThrough setting up a three-dimensional finite element model which be composed of alveolar bone-upper dentition-periodontal ligament-invisible aligners-attachment-resin elastic button,to explore the size of vertical rectangular attachments,materials and thickness of invisible aligners,and the force of class Ⅱ elastics effect on stabilize the canine and fit the invisible aligners when the invisible aligners with class Ⅱelastics,in order to provides reference for the selection of size of vertical rectangular attachments,materials and thickness of invisible aligners,and force of class Ⅱ elastics in clinical practice.MethodsThis study is divided into three parts,and the reading index of each experiment is consistent:part 1:Three finite element models with three vertical rectangular attachments of different heights were constructed,including alveolar bone,upper dentition,periodontal ligament,invisible aligners,attachment,resin elastic button.Places 1N on the canine neck resin button,toward the mandibular first molar of elastic,then reads the canine instantaneous displacement,canine periodontal ligament Von Mises stress,attachment Von Mises stress and the displacement of points:A at the intersection of the distal and buccal and occlusion surfaces of the attachment,Al at the intersection of the inner surface of the invisible orthodontic device,and B at the intersection of the distal,buccal and gingival of the attachment,and B corresponding to point B on the inner surface of the invisible aligner.Finally,the influence of rectangular attachments with different heights on the displacement of the canines and the fitting degree of the invisible aligners to the canines was analyzed and summarized.Part 2:In this experiment,the three models constructed in experiment one were assigned to the 2N force of class II elastics.The influence of different force of class II elastics on the displacement of the canines and the fitting degree of the invisible aligners to the canines was analyzed and summarized.Part 3:The three models constructed in experiment one were assigned to the parameters of three different invisible aligners materials,respectively.The influence of different invisible aligners materials on the displacement of the canines and the fitting degree of the invisible aligners to the canines was analyzed and summarized.In this experiment,the parameters of the invisible aligners materials that are most conducive to the stability of the canine and the fitting of the orthodontic apparatus were selected to conduct a new modeling,set up the correct thickness of 1.00 mm thick.The influence of different thickness of invisible aligners on the displacement of the canines and the fitting degree of the invisible aligners to the canines was analyzed and summarized.Results1.Experiment 1 shows that in rectangular attachments with different heights after elastics is applied,the order of the canine instantaneous displacement and the Von-Mises stress in periodontal ligament from small to large is as follows:4mm attachment<5mm attachment<3mm attachment;The order of the attachment Von-Mises stress from small to large is:5mm attachment<4mm attachment<3mm attachment;In 4mm attachment,the relative displacement of gingival between the canines and the appliance was minimal.In 5mm attachment,the relative displacement of occlusion between the canines and the appliance was minimal.2.Experiment 2 shows that in invisible aligners materials with different force of class II elastics after elastics is applied,the order of the canine instantaneous displacement and the Von-Mises stress in periodontal ligament and attachment from small to large is as follows:1N<2N;In 1N force of class Ⅱ elastics,the relative displacement of gingival and occlusion between the canines and the appliance was minimal.3.Experiment 3 shows that in invisible aligners with different materials after elastics is applied,the order of the canine instantaneous displacement and the Von-Mises stress in periodontal ligament from small to large is as follows:no.3 appliance<no.2 appliance<no.1 appliance(See experiment 3,table 3.2 for details);The attachment Von-Mises stress increases with the increase of the elastic modulus of the appliance.In no.3 appliance,the relative displacement of gingival and occlusion between the canines and the appliance was minimal.In 1.00mm thick orthodontic appliance,the canine displacement,the Von-Mises stress in periodontal ligament and the relative displacement of gingival and occlusion between the canines and the appliance was smaller than 0.75mm thick orthodontic appliance.In 0.75mm thick orthodontic appliance,the attachment Von-Mises stress was smaller than 1.00mm thick orthodontic appliance.Conclusions1.When the invisible aligners is combined with class Ⅱ elastics,it will make the maxillary canines rotate to the distal,tongue and occlusion.2.When only intermaxillary traction is applied,the increase of attachment is beneficial to the stability of the canine and the fitting of the orthodontic appliance in the canine area.However,appropriate attachments should be selected according to the size of the clinical crown of the canine.3.When it is necessary to apply a larger intermaxillary traction force,it should be matched with a larger attachment to prevent the rotation of the canines and dislocation of the invisible aligners appliance.4.When only intermaxillary traction is applied,larger elastic modulus and thicker invisible aligners materials are more conducive to the stability of canines and orthodontic fitting.