Effect Of Different Material Hardness And Designed Displacement On The Biomechanism Of Invisible Appliance

ObjectiveThe purpose of this study was to establish Three-dimensional Finite Element(FEM) models composed of invisible appliance, upper dentition and periodontal tissue and apply the nonlinear method to calculate the models, to compare and analyze the mechanical effect of invisible appliances which had different material hardness and designed displacement respectively, which could provide theory bases for selecting the material of invisible appliance and clinical application.MethodOn the first part, we set up three different FEM models. In these models, the upper central incisor was all planned to move 0.3mm to the mesial and the elastic modulus of material were chosen as 415.6MPa, 816.308MPa and 2400MPa respectively. Then use the Three-dimensional Finite Element model and nonlinear method to analyze the stress and stain distribution in appliance, teeth and periodontal and instant displacement of every teeth.To investigate the change of mechanical effect about three objects.On the second part, we use same method developed another FEM model. In this new model the upper central incisor was planned to move 0.2mm to the mesial and the elastic modulus of material were chosen as 816.308MPa. Analyze the same contents when treatment process is to move upper central incisor mesially respectively for 0.2mm and 0.3mm.Results 1. When elastic modulus of material raised, the stress on the invisible appliance increased and the strain decreased, stress in periodontal and the displacement of aimed teeth increased.2. Under three invisible appliances with different elastic modulus, the initial displacement of the central incisor from crown section was greater than from apical section.3. Under the invisible appliances, the most stress and displacement of teeth was the central incisor, the lateral incisor was the second and in the opposite directions of aimed teeth. When elastic modulus of material decreased, the displacement of the two teeth was closer.4. The invisible appliances with different designed displacement were close to each other in the trend of stress, stain and displacement. When the designed displacement was 0.2mm, stress in periodontal of aimed teeth and displacement was smaller, but stress on invisible appliance was larger.Conclusion1. If the hardness of invisible appliance raised, the displacement of the designed tooth and treatment efficacy increased, but the stress on the appliance and periodontal tissue increased.2. The type of tooth movement was tipping under invisible appliance. Changing the hardness of appliance cannot change the type of tooth movement.3. The teeth adjacent to the aimed teeth moved to opposite direction using invisible appliance and the softer the appliance, the lower capacity the appliance had to control this kind of tooth movement4. Teeth can move efficiently under the invisible appliance with 0.2mm or 0.3mm designed displacement. Compared with 0.3mm designed displacement, the displacement and stress in periodontal of aimed teeth were smaller when the designed displacement was 0.2mm, but the treatment efficacy and stress on invisible appliance were larger.