Orthodontic Treatment of Impacted Teeth. Adrian Becker

Anchorage

      A bypass archwire can be used to connect all teeth on the arch with the exception of the ectopic tooth, to form a rigid stabilizing anchorage unit. It requires a heavy archwire that, for maximum anchorage value, needs to be of rectangular stainless steel wire, which ideally will fill the slots of the brackets. Bypasses are stepped out, with either first‐ or second‐order bends, in order to avoid any interference with the erupting ectopic tooth.

      Using a bypassing arch wire, it is possible to distribute the undesired forces and moments over a larger number of teeth and therefore minimize clinical side effects.

Fig. 3.13 When inverting a left upper canine bracket, it has to be kept in the same side of the arch in order to retain the same distal root tip.

      Because of the low forces engaged in orthodontic treatment in general, the reinforcement of anchorage by using mini‐screws is not usually necessary. Nevertheless, the introduction of skeletal anchorage has potentially widened the spectrum of orthodontics, allowing for treatments that could not previously be done solely with conventional appliances. Biomechanical knowledge is, however, mandatory, in order to ensure that the system is not abused [3].

Useful adjuncts

      Efficient biomechanics are not dependent on additional gadgets. The active, tooth‐moving unit solely concerns the ectopic tooth or teeth. In order to have the facility to apply a cantilever, there need to be auxiliary tubes on the first molars. As the ectopic tooth is brought into the proximity of the arch with traction applied to an eyelet, a bracket has to be substituted to enable controlled alignment. If the tooth is severely rotated and/or tipped, the replacement of the eyelet by bonding a bracket, which carries an additional vertical slot incorporated in the bracket base, will be advised. It should be noted that uprighting and de‐rotation of the canine may be accomplished simultaneously, using a cantilever. Since light forces are used, sufficient anchorage is available with the use of a rigid base arch connecting all the other teeth and consolidating them into a single anchor unit.

      If a lingual arch or transpalatal arch is necessary, Goshgarian tubes, Burstone lingual brackets or hinge cap attachments on the first molars will permit simultaneous multitasking.

      In order to use only light forces, composite cantilevers may be prepared, using a stiffer section in TMA 0.017 in. × 0.025 in. and a more elastic section in TMA round 0.018 in. wire. The stiffer part will secure a tight seat in the auxiliary tube, while the elastic part delivers the needed low force.

Forces applied with a cantilever tied to the eyelet/bracket/ligature wire of the tooth to be moved creating a one‐point contact can be controlled using a Correx tension gauge (Figure 3.14).

Fig. 3.14 The use of a Correx tension gauge is recommended to measure/control the level of the applied forces with cantilevers.

      Straight lengths of new materials, such as the Connecticut New Arch Wire, are bendable and produce lower forces than TMA wire [31].

Super‐elastic Nitinol wire may be used for cantilevers, when bended with the Sander Memory Maker, Khouri Bendistal pliers (Figure 3.15) or hammerhead pliers. Third‐order bends cannot conventionally be bent into super‐elastic wires without destroying the structure of the wire. With the help of the Memory Maker (Figure 3.16), it is possible to programme bends of each order into the NiTi wires, as well as torque [32].

Fig. 3.15 Khouri Bendistal pliers are reliable tools for bending wire ends and V bends.

Fig. 3.16 The Sander Memory Maker allows NiTi wire adjustments in all planes of space and torque application.

Appendix: Colour code convention for moments and forces

      Forces and moments in the three planes of space are depicted as follows:

Table 3.1 Colour code convention.

References

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