Bio-mechanical Study Of Maxillary Anterior Teeth Retraction Treated With Invisible Appliance Combined With Micro-implant Anchorage

[Objective] In this study, we used Nonlinear finite element analysis from Bio-mechanical aspect analysis of the periodontal tissue stress, stress distribution,how different traction effects the displacement of anterior teeth of combined the invisible appliance and micro-implant anchorage and analyzed the maxillary protrusion extraction cases treated by invisible appliance combined with micro-implant anchorage, and the approximate location of the center of resistance was also investigated.so as to provide the theoretical basis for clinical application and scientific guidance.[Methods]Based on the DICOM image files of the maxillary dentition and alveolar bone through spiral CT scanning, the geometry and three-dimensional finite element model of maxillary dentition, alveolar bone, periodontal membrane of maxillary anterior teeth, invisible appliance and micro-implant was established by using MIMICS software and ANSYS finite element software.The magnitude and distribution of the stress of periodontal membrane of maxillary anterior teeth was investigated in the maxillary anterior teeth retraction case treated by invisible appliances and micro-implant by using the non-linear three-dimensional finite element method, so as to speculate the direction of the anterior teeth and the approximate location of the center of resistance.[Results]l.The 3D-finite element model of maxillary cancellous and compact bone of alveolar bone,maxillary anterior dentition, periodontal membrane of maxillary anterior teeth, invisible appliance and micro-implant was successfully established.2. Used Nonlinear finite element analysis from Bio-mechanical aspect analysis of the periodontal tissue stress, stress distribution:When the draw hook height is lmm, the maxillary central incisor and maxillary laterary incisor was found to be the stress concentration zone of the labial and apical surface was relatively small with less stress on the lingual surface, the high stress concentration zone of canine was observed on the mesial and distal surface of the neck of the PDL with more stress on the distal surface. When the draw hook height is 3mm, the maxillary central incisor, maxillary laterary and canine teeth was found to be the magnitude and distribution of the stress of periodontal membrane of maxillary anterior teeth was similar, the high stress concentration zone of the lateral incisor was observed on the distal and partly labial surface of the neck of the PDL with less or even no stress on the mesial surface. When the draw hook height is 5mm and 7mm, the maxillary central incisor, maxillary laterary and canine teeth was found to be the magnitude and distribution of the stress of periodontal membrane of maxillary anterior teeth was similar with 3mm, But tissue stress and distribution than 3mm small.3.Significant changes of the magnitude of the displacement’s direction of the maxillary central incisor and maxillary laterary incisor were observed when applying a loading force of 150g with the draw hook height is 5mm. Significant changes of the magnitude of the displacement’s direction of the canine teeth were observed when applying a loading force of 150g with the draw hook height is 7mm.By the average method the maxillary dentition were observed when applying a loading force of 150g with the draw hook height is 3mm to 5mm.The results through the nonlinear finite element stress analysis to inference the approximate location of the center of resistance.[Conclusion]The geometry and overall three-dimensional finite element model of maxillary dentition, alveolar bone, periodontal membrane of maxillary anterior teeth, invisible appliance and micro-implant were successfully established through spiral CT scanning combined with using MIMICS software and ANSYS finite element software.Thus providing a good platform for the study of the mechanical properties of invisible appliance with a better similarity and simulation.Invisible appliance combined with micro-implant anchorage, under the same traction height, periodontal tissue stress and the initial displacement and load is proportional to the force value;Under the same traction load, draw hook height is 1 mm to 5 mm, maxillary anterior dentition periodontal tissue stress distribution are similar, draw hook height is greater than 5 mm, maxillary anterior dentition periodontal tissue stress distribution range decreases.The conclusions could be drawn according to the magnitude, distribution and the displacement of the stress under different mechanical condition in the anterior teeth retraction case treated by invisible appliance combined with the micro-implant,we can inference the approximate location of the center of resistance:The centre of resistance was located in the position of 3mm to5mm above alveolar ridge.