Biomechanical Characteristics Of Maxillary Anterior Teeth In Customized Lingual Orthodontics By Different Load Patterns During Retracting

ObjectiveTo analyze the biomechanical characteristics of anterior teeth under different loadingconditions when using the customized lingual bracket system during retracting maxillary anteriorteeth with micro-implants and sliding method, and to provide biomechanical reference fordentists choosing the best load pattern to retract maxillary anterior teeth,close extraction space.MethodsSelecting individual normal occlusion of a healthy female volunteer with complete dentitionas modeling material,combining CBCT scanning technology, Mimics14.11, Geomagic Studio12,Pro/E5.0, SolidWorks2013and ANSYS Workbench13.0software applications, a3-D finiteelement model including the e-Brace customized lingual brackets, dentition, periodontalligament(PDL), alveolar bone, arch wire, micro-implants and buccal buckles had beenconstructed and meshed. To determine the direction of the force, connecting the most low-endcenter of hooks and the center of palatal micro-implants,or the center of the buccal buckles andbuccal micro-implants. Including length of2mm,2.2mm and2.4mm of the hooks belonging tothe canine brackets, the anterior teeth movement and the first principal stress in PDL wereanalyzed with different load patterns in which a single palatal force or both buccal and palatalforces(2N).Results1Constructing a3-D FEM modelAn entire3-D FEM model including the e-Brace customized lingual brackets,dentition, PDL,alveolar bone, arch wire, micro-implants and buccal buckles was constructed by this method.Each model which was only different from the length of hooks had40volume models and fullycould meet the need for further research topics.2Effect of different load patterns on displacement of maxillary anterior teeth2.1Effect of different load patterns on displacement of maxillary anterior teeth inhorizontal directionThe displacement of the incisor and the lateral incisor was essentially the same in different loads and overall became stabilized. The mesial cusp of canine showed reduced lingualinclination tendency when palatal load applied while enhanced lingual inclination tendency ondistal cusp when both buccal and palatal loads.When hook was2.4mm, the anterior teeth showed minimal displacement by palatal loadwhile maximum displacement by buccal and palatal loads.2.2Effect of different load patterns on displacement of maxillary anterior teeth in sagittaldirectionThe displacement of incisor overall was stable by different load patterns. Compared withpalatal load, lateral incisor became more stable overall from lingual inclination obviously byboth buccal and palatal loads. The lingual and distal inclination tendency of canine cusp wasobvious.The anterior teeth showed minimal displacement when hook was2.4mm by palatal loadwhile maximum displacement when2.0mm by both buccal and palatal loads.2.3Effect of different load patterns on displacement of maxillary anterior teeth in verticaldirectionMaxillary anterior teeth showed obvious sagging tendency by different load patterns whilethe distal lingual surface of lateral incisor and canine showed depressing tendency. With increaseof length of the hooks, the anterior teeth showed less sagging tendency by palatal load whileincisor and canine showed more sagging tendency by both buccal and palatal loads.The anterior teeth showed minimal displacement when hook was2.2mm by palatal loadwhile maximum displacement when2.0mm by both buccal and palatal loads.3Effect of different load patterns on the first principal stress in PDL of maxillary anteriorteethThe value of the first principal stress of lingual cervix of maxillary anterior teeth wasnegative, showing PDL on pressure.While the buccal cervix was positive, showing PDL ontension.With the increase of length of the hooks, the first principal stress of maxillary anterior teethdecreased by palatal force while decreased obviously then increased by both buccal and palatal forces.Conclusion1The3-D FEM model constructed in this study was labeled with perfect similarity in geometric,mechanics and biology. Consequently the model could meet the needs of subsequent loadingexperiments and analysis relating mechanics problem effectively.2By different load patterns, incisors and lateral incisors showed mildly lingual inclinationtendency in horizontal direction and sagittal direction, and obviously sagging tendency invertical direction. Likewise canine showed obviously displacement tendency in the threedirections.3By different load patterns, the first principal stress of maxillary anterior teeth in PDL wasmainly focused on cervix.When palatal load applied, the maximum value of the first principalstress in PDL showed on the hook which was2.0mm. While both buccal and palate loads applied,the minimum value of the first principal stress in PDL showed on the hook which was2.2mm.