| Background and ObjectiveIn 1935, when the first self-ligating bracket--Russell Lock--born, it did not cause widespread concern in orthodontics doctors. Inventor Jacob Stolzenberg doctor regard the self-ligating bracket haveing lots of advantages, such as reduce referral, the patient feel comfortable, shorten the course of orthodontic treatment, and so on. However, because Russell Lock self-ligating bracket relatively simple structure, the lack of similar Edgewise bracket structure of the wings, and other orthodontic doctors have not been recognized, and eventually did not become a widely used by the self-ligating bracket.since the 1970's, with the development of orthodontic technology, all kinds of self-ligating bracket have been introduced, such as:SPEED (Spring-loaded, Precision, Edgewise, Energy, Delivery) self-ligating bracket, Activa self-ligating bracket, Time self-ligating bracket, TwinLock self-ligating bracket, Damon SL, DamonⅡself-ligating bracket, SmartClip self-ligating bracket and In-Ovation self-ligating bracket.According to forms of slide contacting with brackets slots,above all types of self-lgating bracket generally can be divided into two categories:passive and active. Two kinds of self-ligating bracket all have the features:①eliminates the traditional stainless steel ligation wire or elastic rubber ring.②brackets can limit the treatment arch wire in bracket's slots by using active clip or passive slide.③operation convenient, time-saving operation next chair, and easy to clean. Compared with traditional straight wire bracket, the latest self-ligating brackets not only absorbed straight wire brackets in the orthodontic treatment in the majority of characteristics and performance capabilities, but with many advantages which traditional straight wire bracket does not have. This was greatly promoted the self-ligating bracket in a wide range of orthodontic clinical application. Orthodontic doctors with the United States for more than 10 years has been the use of self-ligating Damon Series Bracket clinical experience.2003,3 M Company introduced Smartclip self-ligating bracket, because simple, easy-to-use, the more successful commercial operation, and attract some of orthodontic doctors who will be its application to clinical practice.In the 1990s, Miao Yaoqiang have used Canada SPEED Bracket attempt. After 2000, China orthodontic doctors aware of the self-ligating bracket advantages, gradually learning in the clinical introduction and try to use. In a few years the clinical application of the process of constantly sum up experience, and self-ligating bracket to explore the use of points, demonstrating its clinical value and prospects. In the use of self-ligating bracket in the process of orthodontic doctors found that self-ligating bracket addition to the aforementioned advantages, such as using light force in treatment, less friction and shorten treatment course. There are also some shortcomings, For example:expensive, dental appliance on the ability to control the three-dimensional drop brackets relatively complex structure, easy to damage.In the United States and Europe, the self-ligating bracket because of good economic prospects, the company has attracted many resources into orthodontic doctors in cooperation with the Research and Development, made a lot of achievements and patents, and its clinical application. Development of self-ligating brackets can not be separated from orthodontic doctors, the same can not be separated from these big companies in research and development.Self-ligating bracket became the successful combination of orthodontic clinical and commercial operation after the MBT straight wire bracket. The self-ligating bracket which China orthodontic doctors used is the majority of the foreign company's products and it's prices more expensive. At present the domestic self-ligating bracket of intellectual property rights less, to the detriment of self-ligating bracket in the promotion and application of our country, there is a need in the self-ligating bracket design study for the establishment of China's own self-ligating bracket knowledge property rights do preliminary exploration.In conclusion of this study used self-ligating bracket on the basis of advantages and disadvantages, design a new type of self-ligating bracket, and the mapping of detailed drawings, produced an enlarged bracket model, the new brackets for laboratory research. This study is divided into two parts: the first part, in a laboratory model of the new brackets friction in vitro experiments on the regulation of different state, the friction brackets ability to control. The second part, with Pro/E software on the new brackets for modeling, using 3D finite element analysis method to simulate the complex mechanics of oral environment, the study of different state, the bracket changes in the internal stress, in the clinical judgement in the application of reliability.Materials and Methods1. Study of adjustable self-ligating bracket on the frictionFirst, we designed a new type of self-ligating bracket, drawing detailed drawings, And applied for a patent (Patent No:ZL200620084676.4)Produced 20 times the size of the steel bracket model, and 20 times the size of the production of steel round wire and wire diameter of 7.2 mm,8.2mm,9.2mm steel round wire (corresponding diameter 0.36 mm,0.41mm,0.46mm round wire), and 9.2 mm x 12.8mm (for 0.46 mm x 0.64mm), and 9.7 x 12.8mm (corresponding 0.485 mm x 0.64mm) steel wire, each arch wire length is 400 mm. As ordinary steel and the friction coefficient between the same stainless steel,the steel of different little effect on the outcome of the experiment.We welded the bracket in a square trough to make sure it will not move, and place two localizers at both ends of the square trough, which are to ensure that the arch wire has no torque and no tip in the bracket。Fasten one end of the sensor for pulling force on the archwire and the other end on the transmission shaft of the electrical machinery, so when the electrical machinery and the gears begin to pull the transmission shaft, the sensor will change the deformation signal into the voltage signal and send it to the compute that will record the changing conditions of the pulling force. Adjust the localizer before the experiment to make it touch the arc wire in a tangent and no pressure condition and its height level with the slot. The electrical machinery and the gears pull the archwire at a speed of 10mm/min. Ireland's study 13has proved that changing of the speed does not affect the magnitude of the frictional force remarkably when the speed of the transmission shaft goes from 0.5 to 50mm/min..Since the FAS unit can up and down by revolving, the position of the shim and archwire can be changed accordingly. The positions of the shim in this experiment fall into four states:the highest, touching the wires in a no pressure and tangent condition, turning a half circle, and turning a whole circle. The slot of bracket in experiment has no tip and torque, wires was putted in center of the slot。Five kinds of wire and four states bring 20 combinations, and every one is tested 10 times. Clean the wires and the bracket with 95% alcohol before the experiment to avoid the lubrication of the greases. The experiment is conducted under a condition of 24℃inside and dryness. Clean the model of the bracket every time the wire is changed in case the abrasion causes the frictional force goes down. Therefore, use the magnifier to observe the frictional plane to confirm that no obvious abrasion occurs. Since the frictional force can be divided into the kinetic and the static, they are recorded respectively. The highest frictional force when the wire just starts to move is stated as the numerical value of the static, while the numerical value when the wire has moved steadily for 3mm is the kinetic。The values of the forces are put into the computer through the sensor, and then are processed by a special software. The SPSS 11.0 software is applied to conducting them statistic analysis.2. The three-dimensional finite element analysis of adjustable self-ligatingbracketFirst choosen imported steel SUS304 as the bracket material in experiment, determine the density of SUS304, Vickers hardness, yield strength, tensile strength, elongation, modulus of elasticity, Poisson's ratio, and other indicators. Used Pro/E software defined unit type, material properties, mesh size of the grid. This model uses the 8-node hexahedral artificial-net, divided into 320 nodes,304 units.In brackets in the mesial-distal-fixed constraints, and in the structure of the upper bracket Centre from 0°-180°loading 200 N load on the surface and then from within the brackets plots to the center bracket covered 0°-180 N°200 loading on the surface load, carried out in the Ansys Workbench for analysis. Application of the self-ligating bracket Von Mises stress (Equivalent stress, stress EQV) peak mechanical assessment.Ansys software used to record the results of experiment.Results1.In the result of this research, to the round wire, there is no significant difference on frictional force between state A and B, and obvious difference in statistics between states A,B and C,D (P<0.01) and difference in frictional forces between state C and D (P<0.01). To the square wires, the frictional force is too strong to be measured under state D, and there is no significant difference in frictional force between state A and B, but obvious difference in statistics between state A,BandC (P<0.01).2.When from different angles on the external surface load loading process, the stress distribution model more similar. Mainly concentrated in the axial stress on the surface, cover and the base occupies a bit (switch). When the external load and model X-axis was 30 degrees, the largest peak stress model.When the trenches internal loading surface in the process of loading the model stress distribution is relatively similar, mainly concentrated in the shaft surface and the gasket and cover with the lower edge of the base interface (switch). When the load and surface model X-axis was 80 degrees, the largest peak stress model.Conclusions1 Round wire and wire care bed in the slide, dynamic and static friction between the significant difference, more than round wire to wire.2 When the gasket in the A, B status, arch wire and brackets contact state and Damon passive self-ligating bracket similar.3 Adjustable upper bracket adjustment device through the rotation, can effectively adjust the size of friction, the friction to control purposes.4 When the adjustable brackets in the mouth by the external surface of the load, the surface shaft, covered with the base occupies a bit (switch) is a major stress on the regional, easily damaged when the external load and a 30 model X-axis degrees, the largest peak stress model.5 When plots internal loading surface in the process of loading, mainly concentrated in the shaft surface and the gasket and cover with the lower edge of the base interface (switch) is a major stress on the region. When the load and surface model X-axis was 80 degrees, the largest peak stress model.6 Whether external or internal loading loading surface load, the stress peaks were less than the yield coefficient of stainless steel, adjustable brackets can withstand the pressure instead of the normal oral permanent deformation occurred.
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