Читать книгу Orthodontic Treatment of Impacted Teeth - Adrian Becker - Страница 60

Root springs (also called alpha–beta springs) can be made from 0.017 in. × 0.025 in. TMA wire. In most cases a truncated V design corresponding to a centred V bend is used.

If the interbracket distance between the displaced tooth and the adjacent tooth is sufficient (>10 mm), intra‐segmental mechanics may also be incorporated in a continuous arch. In order to reduce the load deflection rate, the continuous arch should be made of a rectangular Connecticut New Archwire or NiTi wire. (Note: bends have to be made with a hammerhead plier or the Sander Memory Maker.) A V bend activated in geometry VI will produce molar uprighting by pure rotation. If both units are displaced at the same time, no vertical forces will be generated on either side.

Many other configurations of the root spring/centred V bend are possible. It delivers two equal and opposite moments and no forces. When using a V bend, it is important that the wire has been initially adjusted so that it is completely passive before the V bend is placed (Figure 3.11a, b).

Fig. 3.11 (a) The passive configuration of the alpha–beta spring has to be made and first tested in the mouth. (b) It is recommended to make the V bend activation bend outside the mouth to ensure the geometry corresponds to a geometry VI. The root spring has been activated outside the mouth and reinserted, which produced moments.