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OBJECTIVES: To evaluate, using the finite element method (FEM), the factors that allow control of the anterior teeth during en masse retraction with the Biocreative hybrid retractor (CH-retractor) using different sizes of nickel-titanium (NiTi) archwires and various gable bends on the stainless-steel (SS) archwires. MATERIALS AND METHODS: Using FEM, the anterior archwire section, engaged on the anterior dentition, was modeled in NiTi, and another assembly, the posterior guiding archwire, was modeled in SS. Two dimensions (0.016 × 0.022- and 0.017 × 0.025-inch NiTi) of the anterior archwires and different degrees (0°, 15°, 30°, 45°, and 60°) of the gable bends on the guiding wire were applied to the CH-retractor on the anterior segment to evaluate torque and intrusion with 100-g retraction force to TSADs. Finite element analysis permitted sophisticated analysis of anterior tooth displacement. RESULTS: With a 0° gable bend all anterior teeth experienced extrusion. The canines showed a larger amount of extrusion than did the central and lateral incisors. With a gable bend of >15°, all anterior teeth exhibited intrusion. Bodily movement of the central incisor required a 30°âˆ¼45° gable bend when using anterior segments of 0.016 × 0.022-inch NiTi and 15°âˆ¼30° gable bend with the 0.017 × 0.025-inch NiTi. CONCLUSIONS: With the CH-retractor, varying the size of the NiTi archwire and/or varying the amount of gable bend on the SS archwire affects control of the anterior teeth during en masse retraction without a posterior appliance.

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BACKGROUND:With the development of modern orthodontics, to invent an efficient appliance is the focus in recent studies. Transmission straight wire appliance was born on this background. This appliance can accelerate occlusion and shorten treatment duration. The relationship between distal width and angulation of gable bends of main arch wire needs to study in depth. OBJECTIVE:To establish three-dimensional finite element model of transmission straight wire appliance with better biological and mechanical similarity, and to obtain the relationship between distal width and angulation of gable bend of main arch wire. METHODS:By using scanning of spiral CT with 64 rows, the sectional image data in DICOM format of maxil ary dentition and maxil ae of the volunteers (Class Ⅱ, division 1) were obtained. With the help of Ansys workbench 13.0, Mimics 10.01, Unigraphics NX and Geomagic Studio 8.0 softwares, the three-dimensional finite element model including transmission straight wire appliance, bend, Australian Orthodontic Wire, maxil ae, maxil ary tooth and periodontal ligament was established in Windows XP Service Pack 3 system. RESULTS AND CONCLUSION:A three-dimensional finite element model of transmission straight wire appliance was established, which consisted of 250 929 elements and 657 766 nodes. Furthermore, three-dimensional finite element model had higher geometric similarity and mechanical similarity, as wel as the advantages of adding or subtracting components according to the requirement of the research. The model was conductive to analyze the mechanical system of transmission straight wire appliance and guide the clinical application and appliance modification.

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The purpose of this experimental study was to determine appropriate magnitude of the Gable bends to produce maximum retraction of the anterior teeth. The Calorific Machine was used to illustrate the tooth movement in three dimension. The experimental teeth except the first premolar were embedded in the artificial alveolar bone part. In a series of experiments, the extraction space was closed using arch wires with bull loops into which the gable bends of 10degrees, 20degrees, 30degrees degrees were incorporated. The experiments were repeated three times for each degree of the gable bend. Before and after the space closure, radiographs were taken in the sagittal and occlusal directions using occlusal films. Analysis of variance and Scheffe post hoc test were used to determine significant differences among the three groups. The following results were obtained. 1. As magnitudes of the gable bends increased, more bodily anterior tooth movement was seen and the distance of retraction also increased. 2. As magnitudes of the gable bends increase, the amount of posterior tooth protraction decreased while intrusive and buccal movement increased. 3. The arch was coordinated by distal-in rotation of the canine and mesial-in rotation of the second premolar adjacent to the extraction space.

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This study was designed to investigate force systems and tooth movements produced by retraction archwire during retraction of four maxillary incisors after the maxillary canine retraction into the maxillary first premolar extraction space using the computer-aided three-dimensional finite element method. A three-dimensional finite element model, consisting of 2248 elements and 3194 nodes, was constructed. The model consisted of maxillary teeth and surrounding periodontal membranes, .022" x .028" -slot brackets, and 5 types of retraction archwires(.019" x .025" stainless steel archwire) modeled using the beam elements. The contact between the wire and the bracket slot was modeled using the gap elements because of the non-linear elastic behaviors of the contact between them. The forces and moments, and displacements produced by retraction archwire were measured at various conditions to investigate the difference according to types of loops, magnitudes of activation force, gable angle, and anterior lingual root torque. The results were expressed quantitative and visual ways in the three-dimensional method. The following conclusions can be drawn from this study: 1. When the tear-drop loop archwire was activated, the mesio-distal and lingual translational movements of the teeth helped to close the extraction space, but unwanted movements of the teeth including intrusions and extrusions, and rotational movements in each direction occurred. 2. Activation of T-loop archwire compared with those of other types of retraction archwires produced the least translational movements of the teeth helped to space closure and also the least unwanted movements of the teeth. 3. Increasing amount of activation in the tear-drop archwire led not only to increase of translational movements of the teeth helped to space closure, but also to increase of unwanted movements of the teeth. 4. Addition of gable bend in the tear-drop archwire helped anterior teeth to translational movements in the mesio-distal direction, but increased unwanted movements of the teeth. 5. Addition of anterior lingual root torque in the tear-drop archwire helped central and lateral incisor to improve their facio-lingual inclination, but increased unwanted movements of the teeth.

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