| Objective: By means of three-dimensional finite element analysis,the stress distribution and tooth displacement of the root and periodontal ligament of the maxillary central incisor with normal shape and abnormal short root in the invisalign orthodontic treatment under the same orthodontic force and different movement modes were compared and analyzed.The stress distribution law and tooth movement trend of the periodontal ligament of the root were summarized,which could provide reference for the design of invisalign orthodontic treatment scheme and clinical treatment.The clinical risk of patients without short root abnormality(SRA)during orthodontic treatment.Methods: From August 2016 to August 2017,three adult volunteers(1:1.3,1:1,1:0.7 clinical crown-to-root ratio of maxillary central incisors)were selected from the orthodontic Department of Lanzhou University Stomatological Hospital.The maxillofacial images were taken by CBCT and reconstructed by Mimics software using Geomagic and Proagic./ The three-dimensional finite element models of maxillary dentition,alveolar bone,periodontal ligament and invisible appliance were established by E and other related software.The loads corresponding to distal movement,press-in movement and palatal movement were applied.The stress and displacement of the root and periodontal ligament of the maxillary central incisors with different crown-root ratios and with the same crown-root ratio under the same loads and with the same clinical crown-root ratio under different movement modes were studied.The trend is analyzed and compared.Results:(1)Three groups of maxillary central incisors with different clinical crown-root ratios were constructed,and the ratios were 1:1.3,1:1,1:0.7;(2)The root stress of three groups of maxillary central incisors with different clinical crown-root ratios was mainly located in the far-middle surface of the root neck,while the periodontal ligament stress was mainly located in the near-far-middle surface of the root neck;during the process of compression,the root stress was mainly concentrated in the root.The shorter the root is,the closer the periodontal ligament stress is to the apex,the longer the root is,the more the maximum stress of the periodontal ligament deviates to the neck of the tooth;in the process of adduction,the greater the root stress is located in the neck of the lingual tooth root,and the periodontal ligament stress mainly distributes in the neck of the tooth root and in the middle of the root 1/3.The shorter the root is,the more concentrated the stress is,the longer the root is,the more uniform the stress distribution is;(3)For the same case.During the process of crown-root ratio reduction,the high stress range of periodontal ligament was the largest,mainly concentrated in the apex and the lingual side of the root;(4)When moving far,the left upper central incisor moved toward the crown and lip,and the change of displacement was most obvious in the Z-axis direction,with R/C greater than 1,the displacement decreased significantly;when the crown was pressed low,the displacement of the distal and middle lip tended to move.The most obvious change of displacement is the direction of X-axis,with R/C greater than 1,the displacement decreases obviously;in addition,the displacement changes most obviously in the direction of X-axis,and with R/C greater than 1,the displacement decreases obviously.Conclusions:(1)In the three groups of maxillary central incisors with different crown-root ratios,the stress distribution of the root and periodontal ligament is quite different in the process of distal,compression and adduction movement.The shorter the root is,the more concentrated the stress is,the longer the root is,and the more uniform the stress distribution is.(2)For the same clinical crown-root ratio of maxillary central incisors,the risk of root resorption during distal,depression and adduction may be higher than that during distal and adduction movement.(3)In invisible orthodontics,the tooth movement is inclined,and the center of rotation is located at the root below the neck.(4)Reducing the deformation of the invisible appliance can effectively reduce the stress value of the stressed root and periodontal ligament.Short root abnormality is not a contraindication of orthodontic treatment.For different clinical crown-root ratio teeth,as long as the force value is loaded within its affordable range,it will not cause root resorption. |
