Page 106 - REMOVABLE ORTHODONTIC APPLIANCES

98 Removable Orthodontic Appliances
• The appliance is withdrawn from the mouth. emerges on the buccal side of the arch so that
• The arm of the force gauge can then be the coil is correctly positioned. The coil itself
pushed against the spring to return it to the can then be grasped in the beaks of the spring
mark on the baseplate. The force that will be forming pliers and the free end flexed with the
delivered to the tooth can then be read. thumb to the desired position.

Secondary adjustments
Buccal springs
Both buccal and palatal springs may require
A buccal spring can be checked by measuring further adjustment. In the case of a palatal
the position of the spring tip relative to the finger spring, the height may need adjustment
mesial arrowhead of the molar clasp on that so that the spring rests just clear of the gingival
side. This can be done with a pair of spring margin. If the wire projects too far buccally it
dividers when the appliance is in the mouth. may cause trauma to the cheek and require
The appliance is removed from the mouth and shortening. If a guard is being used care must
the arm of the force gauge again used to flex the be taken to see that the spring slides smoothly.
spring back into its original place. A buccal spring may also require adjustment
It is not necessary to measure force routinely for height and it may be necessary to flex the
in this manner, but it does help the operator to free end of the spring inward with the thumb so
assess the amount of activation that will deliver that it engages the tooth firmly, or sometimes
the required force. Once this activation, has to flex the entire spring inwards if the coil is too
been assessed it is still often useful to mark the prominent.
position of a palatal spring with a wax pencil When such adjustments have been carried
when the appliance is in position. The position out it is necessary to re-check that the spring
of a buccal spring can be measured in the way activation has not been inadvertently altered.
described so that the actual amount of activa-
tion can be seen more easily.
Labial wires
Buccal canine retraction springs The general principle of avoiding existing
bends during activation and of carrying out the
Activation is carried out by holding the spring adjustment at different points still applies.
close to the coil with the plier beaks and flexing
incisors
may
be
it with a finger or thumb until the desired posi- Where the to combine are irregular it grinding
careful selective
necessary
tion is reached. During activation the spring is of the palatal acrylic with activation of the
permanently deformed by bending it beyond its labial wire. The wire may also be kinked to
elastic limit. It is good practice to avoid bend- bring pressure to bear on a particular tooth and
ing the spring at places where the Vire has been so help in obtaining alignment.
bent during its formation and also to avoid
carrying out successive activations at the same Again, it is possible to measure activation of
position. It should be remembered that activa- anterior wires and this can be done by drilling
tion of a spring offers a chance to modify the a small pin-hole into the acrylic of the anterior
direction of tooth movement. bite plane and measuring from this to the mid-
point of the labial wire, which can be marked
An appliance may sometimes be constructed with a wax pencil. The difference between this
with the coils of the canine finger springs, for measurement taken with the appliance in and
example, placed too far distally. Simple activa- out of the mouth will show the amount of acti-
tion of the spring from the coil will move the vation (Figure 10.16). A spring gauge can be
canine buccally as it is retracted. A crank used to produce the same amount of deflection
progressively placed into the spring will and so indicate the force being used.
provide activation and help to limit this
tendency. When such cranking is not necessary
the bend should be placed near to the coil.
The labial bow
In the case of a buccal spring it may often be
necessary to adjust the spring at more than one This is activated by reducing the size of the
point. The wire can be bent near to where it loops. Each side is dealt with individually by