| Objectives Using three-dimensional finite element method,the models of maxillary alveolar bone,maxillary anterior dentition,periodontal ligament and invisible appliance without brackets is established,and the displacement trend of the right maxillary central incisor with different root lengths and the force of periodontal ligament are analyzed.By adjusting the torque angle of the invisible appliance,further study the displacement trend of the right central incisor of the maxillary and the force of the periodontal ligament after the non-bracket invisible appliance is loaded with lingual torque,in order to improve the invisible appliance The effect of lowering the maxillary anterior teeth provides a theoretical basis.Methods 1 A volunteer with normal tooth morphology and size,healthy periodontal tissue,and established permanent teeth occlusal relationship was selected for oral and maxillofacial CBCT scan.2 The scanning data were transferred to Mimics 19.0 software by computer and transformed into the preliminary maxillary alveolar bone and anterior dentition models,Geomagic Studio13.0 and UG 10.0 software were used to construct the periodontal membrane and brackets less invisible appliance models,and each structure was further optimized and assembled to form the overall model.3 Modified the already formed model to obtain a maxillary alveolar bone-anterior dentition-periodontal ligament model with the crown-to-root ratio of the right maxillary central incisor of 1:1.4 According to the purpose of the experiment,the experimental models were divided into two groups of 6groups.The right maxillary central incisor of group A was set with different root lengths,the crown-to-root ratio of the right maxillary central incisor of group A1 was 1:1.3,and the right maxilla of group A2 The crown-to-root ratio of central incisors was 1:1;the model of group B adds lingual torque on the basis of group A1,the appliance of group B1 was preset with 1° lingual torque,and the appliance of group B2 was preset with 3° lingual torque,the appliance of group B3 was preset with 5° lingual torque,and the appliance of group B4 was preset with 7° lingual torque.The models were loaded with 0.20 mm along the root of the long axis of the maxillary central incisor,and calculated by ANSYS Workbench 18.1software to obtain the data cloud chart of the displacement trend and periodontal ligament distribution of the right maxillary central incisor under different conditions,and analyzed.Results 1 The models of maxillary alveolar bone,maxillary anterior dentition,periodontal membrane and invisible orthodontic appliance without brackets were successfully established.2 The upper central incisors in both groups A1 and A2 were inclined to move from the crown lip to the root tongue while being depressed,and the degree of tilt in group A2 was greater than that in group A1.3 The root lip movement of maxillary central incisor increased and the crown lip movement decreased after torque was added;when the angle was 5°(ie,B3 group),the movement from crown lip to root tongue became the movement of crown and root tongue;when the angle was 7°(ie,B4 group),it became the movement of the crown tongue to the root lip direction;the crown pressure of maxillary central incisor was B1>B2>B3>B4.4 In the experiments of group A and group B,the stress of periodontal membrane was mainly concentrated in the neck and apical region of periodontal membrane;the periodontal membrane stress distribution in group A2 was more concentrated,and the periodontal membrane stress value was A2>A1;the periodontal membrane stress values of group B were B4>B3>B2>B1,and the periodontal membrane distribution of group B3 was more uniform,and there was no obvious stress concentration point at the root tip.Conclusions 1 The finite element model constructed by CBCT combined with Mimics19.0,Geomagic Studio 13.0 and other software has good geometric similarity,which is conducive to the subsequent experiments.2 When the maxillary central incisor is lowered with invisible appliance,maxillary cenral incisor with a crown-to-root ratio of 1:1 is more susceptible to tilting movement of the crown lip towards the root tongue,and is at higher risk of root resorption than maxillary central incisor with a crown-to-root ratio of 1:1.3.3The loading of lingual torque angle of the invisible orthodontic device can achieve the overall depression of the maxillary central incisor,but it weakens the tendency of tooth depression,and the periodontal membrane stress increases;when the angle is 5°,the crown-root ratio of 1:1.3 maxillary central incisor tends to move as a whole.Figure 20;Table 6;Reference 124... |
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