Correcting Torsiversion Torsiversion is a medical condition in which a tooth is rotated away from its normal position about the long axis of the root. Studies show that about 2 percent of the population suffer from this condition to some degree. For those who do, the improper alignment of the tooth can lead to tooth-to-tooth collisions during eating, as well as other problems. Typical patients display a rotation ranging from 20 ∘∘ to 60 ∘∘ , with an average around 30 ∘∘ . An example is shown in the figure(Figure 1), where the first premolar is not only displaced slightly from its proper location in the negative yyy direction, but also rotated clockwise from its normal orientation. To correct this condition, an orthodontist might use an archwire and a bracket to apply both a force and a torque to the tooth. In the simplest case, two forces are applied to the tooth in different locations, as indicated by F1F1 and F2F2 in the figure (a). These two forces, if chosen properly, can reposition the tooth by exerting a net force in the positive yyy direction, and also reorient it by applying a torque in the counterclockwise direction. In a typical case, it may be desired to have a net force in the positive yyy direction of 1.8 NN. In addition, the distances in the figure (a) can be taken to be ddd = 3.2 mmmm and DDD = 4.5 mmmm. Given these conditions, a range of torques is possible for various values of the yyy components of the forces, F1yF1y and F2yF2y. For example, the figure(Figure 2) shows the values of F1yF1y and F2yF2y necessary to produce a given torque, where the torque is measured about the center of the tooth (which is also the origin of the coordinate system). Notice that the two forces always add to 1.8 NN in the positive yyy direction, though one of the forces changes sign as the torque is increased.
Correcting Torsiversion Torsiversion is a medical condition in which a tooth is rotated away from its normal position about the long axis of the root. Studies show that about 2 percent of the population suffer from this condition to some degree. For those who do, the improper alignment of the tooth can lead to tooth-to-tooth collisions during eating, as well as other problems. Typical patients display a rotation ranging from 20 ∘∘ to 60 ∘∘ , with an average around 30 ∘∘ .
An example is shown in the figure(Figure 1), where the first premolar is not only displaced slightly from its proper location in the negative yyy direction, but also rotated clockwise from its normal orientation. To correct this condition, an orthodontist might use an archwire and a bracket to apply both a force and a torque to the tooth. In the simplest case, two forces are applied to the tooth in different locations, as indicated by F1F1 and F2F2 in the figure (a). These two forces, if chosen properly, can reposition the tooth by exerting a net force in the positive yyy direction, and also reorient it by applying a torque in the counterclockwise direction.
In a typical case, it may be desired to have a net force in the positive yyy direction of 1.8 NN. In addition, the distances in the figure (a) can be taken to be ddd = 3.2 mmmm and DDD = 4.5 mmmm. Given these conditions, a range of torques is possible for various values of the yyy components of the forces, F1yF1y and F2yF2y. For example, the figure(Figure 2) shows the values of F1yF1y and F2yF2y necessary to produce a given torque, where the torque is measured about the center of the tooth (which is also the origin of the coordinate system). Notice that the two forces always add to 1.8 NN in the positive yyy direction, though one of the forces changes sign as the torque is increased.
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