A study on the pattern of movement during retraction of maxillary central incisor by finite element method / 대한치과교정학회지

The retraction of anterior teeth is one of the fundamental methods in orthodontic treatment and a proper position and angulation of anterior teeth after the retraction are very important for esthetics, stability, and function of teeth. In this research we analyzed, by Finite Element Method, the stress distribution on the periodontal ligament according to the variation of force and moment applied on the crown and predict the pattern of movement of maxillary central incisor. At the same time, the amount of force and moment caused by activation of the loop which was used for retraction of maxillary central incisor was analyzed by Finite Element Method. We observed the following results: 1) We could control the stress distribution on the periodontal ligament by proper moment/force ratio on maxillary right central incisor and predict the pattern of movement of maxillary right central incisor. 2) The amount of stress on the periodontal ligament as well as the moment/force ratio demanded by each pattern of movement increased as the destruction of alveolar bone was worse. 3) The moment/force ratio demanded by each pattern of movement decreased as the angle between the maxillary central incisor and occlusal plane decreased. 4) The force with the open loop was shown to be large compared to that with the closed loop. Also, the force with the helix decreased by 30% compared to that without the helix. 5) Under the same conditions we observed a larger moment/force ratio when the open loop and/or the helix were used.

Three / 대한정형외과학회잡지

Since the finite element method(FEM) was introduced to the orthopaedic biomechanics, it has been applied with increasing intrest to investigate bone, bone-prosthesis, and fracture fixation device, etc., in terms of stress, strain, force, and displacement. The authors implemented the FEM for the "intact" and the "fractured long bone models respectively to observe the mechanical behaviors of the plate fixation for the long bone fractures, and we observed the followings;l. In the intact model, stresses are evenly distributed and smoothly changed. 2. The maximum equivalent von-Mises stress in the fracture model is higher than that in the intact one. 3. Stresses on the plate are much higher than those on the bony surface in the fracture model. 4. Stresses for the bony surface beneath the plate in the fracture model are much lower than those in the intact model;however, stresses are highly concentrated around the screws. 5. Although two-thirds of total compressive load is transmitted through the fracture site area, maximum von-Mises stress in the fracture site is much lower than that in the plate. 6. High stresses are found at the areas between the plate holes and the screw heads. 7. Shearing forces of the screws are higher at the near and end screws from the fracture site.