Читать книгу Orthodontic Treatment of Impacted Teeth - Adrian Becker - Страница 61

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°).