Page 34 - REMOVABLE ORTHODONTIC APPLIANCES

26 Removable Orthodontic Appliances
Figure 3.24 Self-straightening wires (0.5 mm) on a
labial bow (0.7 mm). Self-straightening wires are
wound loosely on to the bow so that they can slide
freely along it. (a) A labial view, (b) A palatal view
showing the self-straightening wires in their passive
position.

Self-Straightening wires of bow will prevent buccal drift of the canines
during their retraction, but the primary method
A modification of a labial bow to increase its flex- of controlling canine movement should be by
ibility can be made by adding a self-straightening correct adjustment of the spring, rather than by
wire, which can be used to reduce an overjet relying on the bow to compensate for careless
(Figure 3.24). Individual tooth movements adjustment. This bow is rather rigid and should
cannot be undertaken and there is a tendency for be activated by only 1 mm at any time.
this device to flatten the arch anteriorly, although
the use of two wires will minimize this tendency.
Adjustment
The adjustment is carried out in two stages
Adjustment
(Figure 3.26). The vertical loop is first opened
This is done by closing the 'U' loops of the bow by compressing it with pliers. This lowers the
and adjusting its level as necessary. Care must bow in the incisor region so that compensating
be taken to ensure that self-straightening wires bends must be made at the base of the loops.
run freely on the supporting bow. The flexibility of the bow with reverse loops
can be improved either by dividing it or by
adding self-straightening wires, as described
above for the labial bow with 'U' loops.
Labial bow with reverse loops
This is similar to the bow described above
except that reverse loops are used (Figure Extended labial bow
3.25). These loops must be well clear of the
clasps on the first molars or they will be difficult This labial bow is also made from 0.7 mm wire
to adjust. It is sometimes claimed that this type but its flexibility is greatly increased by the