and reinserted, which produced moments.
Torqueing auxiliaries/torque application
Ectopic teeth brought into the arch may require torque application. For torqueing a single tooth the use of auxiliary springs may be the preferred solution. Warren spring auxiliaries can torque the canine independently [29]. When an archwire–Warren spring combination for palatal crown torque is used with a full‐size archwire, the spring is bent to push against the incisal part of the crown, but no torque movement will occur because the edgewise wire will twist to produce lingual root torque, thereby making this appliance inappropriate [1]. This auxiliary must be placed on a round or undersized rectangular wire in order to make the mechanism a valid one [1]. Wires adjusted to torque individual teeth should be sufficiently undersized to allow the wire to rotate in the slot of the adjacent tooth with no reciprocal torque reaction on that tooth. This precaution is more easily observed with a 0.022 in. slot than with a 0.018 in. bracket slot [30].
A good alternative is the von der Heydt torqueing auxiliary on a heavy passive round arch. This auxiliary is formed from 0.014 in. or 0.016 in. hard stainless steel wire and placed under a passive base arch of 0.018 in. or 0.020 in. round stainless steel. Simply by tying the two arms of the auxiliary into the brackets, piggyback style down to the main arch, torque is introduced to rotate the long axis of the tooth around the main arch (Figure 3.12a, b). It may incorporate two spurs for torqueing both central incisors or four spurs for all four incisors concurrently. It may be used for labial root torque by pointing the spurs above the brackets. For lingual root torque, the auxiliary is inverted, with the spurs point inferiorly to the brackets. Since it is it is supported by a round base arch, this mechanism cannot cause reactive lingual root torque on the adjacent incisors – no ‘round‐tripping’.
Fig. 3.12 (a, b) A 0.016 in. main arch is combined with a 0.016 in. von der Heydt torqueing auxiliary engaged in 0.018 in. × 0.025 in. brackets.
The von der Heydt auxiliary is routinely used in the Begg technique, has a very long range of action and a single activation is often adequate to complete a significant degree of torque. However, should the patient not attend for routine observation and adjustment, a few extra weeks can sometimes find the root apex bulging the oral mucosa.
A 0.016 in. main arch will need reinforcement if it is to supply the needed anchorage. The possible reinforcements would need to include one or both of a more substantial compensatory curve of the main arch or a Goshgarian or soldered transpalatal arch.
Furthermore, the use of available variable torque options may help to achieve the required root torque. In more demanding cases, reverse torque can be employed by inverting the bracket to change the torque value from positive to negative or vice versa (Figure 3.13).
The effective torque of inverted brackets is dependent on the preferred bracket prescription. For instance, an inverted upper canine bracket of the McLaughlin‐Bennett prescription will not deliver buccal root torque, but will deliver an increased inclination of 14° (from –7° palatal root torque to 7°).
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
