Page 26 - REMOVABLE ORTHODONTIC APPLIANCES

18 Removable Orthodontic Appliances
Springs are not normally made in wire diam-
eter of less than 0.5 mm, as the patient would
readily distort thinner wire and they are not
generally recommended.
To give a spring a degree of stability while
still retaining flexibility, 0.5 mm wire can be
sheathed with stainless steel tubing having an
internal diameter of 0.5 mm. The tubing is then
incorporated into the acrylic of the appliance.
Such supported springs are used for canine
retraction and overjet reduction (Figure 3.6). Figure 3.8 A supported buccal canine retractor to
Unsupported buccal springs (Figure 3.7) and move the tooth distally and palatally.
bows have to be made from 0.7 mm wire to
provide sufficient strength. Unsupported buccal
springs are often rather stiff. Such springs must buccal spring must be used if palatal movement
not be activated by much more than 1 mm, if is required, or if it is not possible to engage a
excessive force is to be avoided. Because the palatal spring correctly on the tooth surface
force decays rapidly as the tooth moves, the (Figure 3.8).
spring may not remain active throughout the
period between visits. This means that continu-
ous tooth movement is difficult to maintain.
Ease of insertion and patient comfort
Most springs are readily managed by the
Direction of tooth movement patient but, if palatal finger springs are used to
move cheek teeth buccally then correct inser-
The point of contact between the spring and tion may be difficult and'T' springs (Figure 3.9)
tooth determines the direction in which the are preferable. Most palatal springs are
tooth moves. A palatal spring is satisfactory for comfortable but the ends must be carefully
labial and mesio-distal tooth movements, but a finished to avoid lacerating the patient's buccal
mucosa.
Buccal springs and bows can cause discom-
fort and traumatic ulceration if they have been
extended too deeply into the sulcus or if they
project buccally, so care must be taken to posi-
tion such springs correctly when fitting the
appliance.

Figure 3.6 A supported buccal canine retractor
0.5 mm wire sheathed in stainless steel tubing.

Figure 3.9 A 'T' spring constructed from 0.5 mm
Figure 3.7 Unsupported buccal canine spring wire. Adjustment loops are incorporated so that the
0.7 mm. spring can be elongated as the tooth moves buccally.