Читать книгу Orthodontic Treatment of Impacted Teeth - Adrian Becker - Страница 48

Cantilevers are useful in the delivery of a single extrusive and/or lateral force. A cantilever system is characterized by a pure force acting at its extremity (the free end) with single‐tooth contact. Its other end is engaged in a bracket, slot or tube, where it exerts an equal and opposite force and a moment [12, 13]. The cantilever system may be used in many modifications. As a rule, the cantilever should be as long as possible in order to decrease the force and increase the deflection (activation distance or range). The auxiliary tube of the first molar bands is most suited for engaging the cantilever, since it prevents excess play in the tube. It will accept a 0.016 in. × 0.022 in. cantilever wire in a 0.018 in. or a 0.017 in. × 0.025 in. cantilever wire in a 0.022 in. strap‐up.

With a statically determinate force system, where forces and moments are either known or measurable, the behaviour of the impacted tooth is mostly predictable. Impacted teeth need movement in two directions. An eruptive force is needed to bring the tooth to the level of the occlusal plane and a horizontal (buccal or mesio‐distal) force to bring the tooth into alignment in the arch. This may be achieved using a cantilever. However, it may also be achieved using a triangular elastic (1/4 in., 6 mm/70 cN) to the two opposing teeth, provided that they are engaged in a rigid continuous archwire in the opposing arch.

Cantilevers are made either of beta‐titanium (TMA) wires, Connecticut New Archwires or nickel–titanium (NiTi) wires. When using NiTi wires, bends should ideally be made with a hammerhead plier, or the Sander Memory Maker, to maintain the desired cantilever shape. Using a range of different types of wire for cantilever construction allows the orthodontist to use light forces, which can easily and usefully be measured with a gauge, in combination with long ranges of activation.