A Three-dimensional Finite Element Study On The Expansion Of The Width Between The Maxillary First Molars With The Invisible Appliance

ObjectiveThrough the establishment of a three-dimensional finite element model of maxillary bone-periodontal ligament-teeth-attachment-invisible appliance to explore different conditions(attachment position,size and appliance elastic modulus)on the invisible appliance to expand the width of the maxillary first molar,in order to provide a reference for the plan design and material selection when using invisible appliance to expand dental arch.MethodsThis experiment is divided into three parts:Experiment 1:Three kinds of finite element models are established according to the changes of attachment position.Set the maxillary first molar buccal to whole mobile 0.25 mm,and calculate the overall instantaneous displacement of the maxillary first molar and instantaneous displacement of the observation points(crown observation points:mesial buccal point,mesial palatal point;root observation points:mesial buccal root tip point,palatal root tip point),the ins-tantaneous displacement of anchorage teeth and the stress of the periodontal ligament of the maxillary first molar under various working conditions.Analyze the influence of attachment position change on enlarging the width of the maxillary first molars with invisible appliance..Experiment 2:Choose the best attachment position according to the conclusion of Experiment 1,and establish three finite element models of horizontal rectangular attachment with different lengths at this position.Displacement loading and calculation indicators are the same as those in Experiment 1,analyze the influence of attachment size changes on the expansion of the width of the maxillary first molars with invisible appliance.Experiment 3:According to the conclusions of Experiment 1 and Experiment 2,choose the best position and the most suitable length of the attachment,and establish three kinds of elastic modulus finite element models of the invisible aligner.Displacement loading and calculation indicators are the same as those in Experiment 1,analyze the influence of invisible appliance materials with different elastic modulus on the expansion of the width of the maxillary first molar.Results1.Experiment 1 shows that in different models,the maxillary first molars mainly show the tendency of buccal movement,the instantaneous displacement of the observation points of the crown and root,the overall instantaneous displacement,and the stress value of the periodontal ligament of the maxillary first molar are shown as no attachment group<buccal attachment group<lingual attachment g-roup,in which the displacement increase of the observation point of the crown is significantly greater than the displacement increase of the observation point of the root;The instantaneous displacement of anchorage teeth has more obvious effects on straighten the maxillary second premolar and the maxillary second molar on both sides of the orthodontic teeth,and the displacements are shown as no attachment group<buccal attachment group<lingual attachment group.2.Experiment 2 shows that in the horizontal rectangular attachments of different lengths,the direction of the instantaneous displacement of the maxillary first molar is the same as that in Experiment 1,but the instantaneous displacement of the observation points of the crown and root,the overall instantaneous displacement,and the stress value of the periodontal ligament of the maxillary first molar are shown as 3 mm attachment<4 mm attachment<5 mm attachment,but the increase is not obvious.The direction of the instantaneous displacement of the anchorage teeth is the same as that in Experiment 1,and its displacements are shown as 3mm attachment<4mm attachment<5mm attachment.3.Experiment 3 shows that in appliances with different elastic modulus,the direction of the instantaneous displacement of the maxillary first molar is the same as that in Experiment 1,but the instantaneous displacement of observation points of the crown and root,the overall instantaneous displacement,and the stress value of the periodontal ligament of the maxillary first molar are shown as group 1 appliance(415.6Mpa)<group 2 appliance(528Mpa)<group 3 appliance(816.31Mpa),in which the displacement increase of the observation points of the crown is significantly greater than the displacement increase of the observation points of the root.The direction of the instantaneous displacement of the anchorage teeth is the same as that in Experiment 1,and its displacements are shown as group 1 appliance(415.6Mpa)<group 2 appliance(528Mpa)<group 3 appliance(816.31Mpa).Conclusions1.The invisible appliance can expand the width of the maxillary first molar mainly by tooth buccal oblique movement.2.Setting a horizontal rectangular attachment on the lingual side of the maxillary first molar is more conducive to achieving arch expansion,and the larger the length of the attachment,the greater the displacement of the molars.3.The invisible appliance material with higher elastic modulus(816.31Mpa)is more conducive to expanding the width of the maxillary first molar.4.When the invisible appliance expands the width between the maxillary first molars,the adjacent teeth on both sides of the orthodontic tooth show the opposite displacement as anchor teeth,and the larger the size of the lingual rectangular attachment of the orthodontic tooth and the elastic modulus of the appliance,the more difficult it is to control this displacement.