| Orthodontics is a complex process of tooth movement. In orthodontic clinical treatment we often involves the question of extraction. In nearly a century of the development of orthodontics, various orthodontists in each periods held different attitudes on tooth extraction because of the development of orthodontic theory and techniques. Orthodontic tooth extraction rate in every era appeared a process from low to high and then descend. Orthodontic treatment with extraction possess certain percentage in contemporary era of orthodontic clinical treatment. On the one hand, extraction increase the difficulty of orthodontic treatment. On the other hand it needs more treatment time relatively. So researching the relationship between orthodontic appliances and treatment with extraction involve important clinical significance. And how can we improve the speed of tooth movement and quality in the process of extraction , simplify the treatment process and shorten the course of treatment become a important clinical problem which orthodontists are caring for.Since Edgewise fixed appliance was designed, many fixed appliance came out continuously. Each fixed appliance has its own characteristic and dominance and the effect of teeth movement which every fixed appliance make is different. A new fixed appliance occur accompany with a new orthodontic theory. Dozens of fixed appliance had been used in orthodontic clinical treatment. Some of them are still being used by orthodontists. Today, the most widely used orthodontic appliance is Edgewise fixed appliance and the straight wire appliance which was developed from the basis of Edgewise fixed appliance. Straight wire appliance is a qualitative leap of edgewise fixed appliance .Straight wire appliance entrust the data in the brackets, reduce unnecessary wire preparation and operation time. At the same time, the treatment concept of the straight wire appliance is more advanced than of the Edgewise fixed appliance. Straight wire appliance has been used popularly in China. The all programmable straight wire appliance and MBT straight wire appliance accounted for the majority of that used in clinic.The MBT straight wire appliance is more convenient for orthodontic treatment in the patients with extraction by its light power and sliding mechanics. Meanwhile, the Tip-Edge orthodontic appliance based on Begg orthodontic technology can make teeth move quickly by differential and declivent movement. The effect is obviously applied in patients with extraction. However, the mechanics of tooth movement caused by fixed appliance have not been elucidated. This experiment calculate the the instantaneous displacement of the teeth and stress force on surface of the teeth root , analyze biomechanics in extraction sample which is treated by Tip-Edge Plus and MBT straight wire appliance by the method of three dimensional finite to investigate the characteristic and dominance of the two appliances. Then the result can provide some references to the clinical practice in theory.The model for this study comes from a young male volunteer's maxilla and maxillary dentition. The characteristic include such aspects: Individual normal occlusion, complete dentition, no caries, arch symmetrical, class 1 molar relationship, teeth arranged regularly and periodontium is healthy. This experiment employed helicon-CT to scan the maxilla and maxillary dentition by 0.7mm-thickness layer, re-establish the maxilla bone and teeth , divide grid and finished assembly by software of Mimics and Ansys. Thus, we get the three dimensional model for mechanic analysis.The result of this experiment is: The instantaneous displacement of the teeth and stress force on surface of the teeth root using Tip-Edge Plus appliance is larger than that of using MBT appliance.The instantaneous displacement of the teeth become larger when the force increase, so is the stress force on surface of teeth by using Tip-Edge Plus appliance. The tendency of teeth movement using MBT appliance is similar, but the amount is small relatively.The conclusion of this experiment is: (1).The instantaneous displacement of the teeth and stress force on surface of the teeth root using Tip-Edge Plus appliance is larger than that of using MBT appliance.(2).The instantaneous displacement of the teeth become larger when the force increase, so is the stress force on surface of teeth by using Tip-Edge Plus appliance. The tendency of teeth movement using MBT appliance is similar, but the amount is small relatively.(3)The friction force between appliance and wire of Tip-Edge Plus appliance is smaller than that of the MBT appliance, so is the force of resistance. (4).The passive motion scope of Tip-Edge Plus appliance is bigger than that of MBT appliance when using the same force. And the teeth are tend to move to the extraction gap. (5). Tip-Edge Plus appliance is more suitable for orthodontic treatment of patient with teeth extraction by contrast. |
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