Page 105 - REMOVABLE ORTHODONTIC APPLIANCES

Chairside management 97
that treatment will be lengthy. In very rare
cases, treatment may be prolonged by the pres-
ence of dense alveolar bone. Although the
problem is rare, a similar situation can arise
where a tooth, often an upper canine, is
buccally displaced into the cortical plate. The
bone surrounding the root is dense and lamel-
lar and if the tooth is moved parallel to the line
of the arch progress will be slow. Such a tooth
should be moved into the line of the arch by the Figure 10.14 Correct degree of activation of a
shortest path and then retracted through the canine spring. The spring should just contact the
mesial incline on the canine before full insertion of
cancellous bone of the alveolar process.
the appliance.
Has the appliance been worn as
instructed? provides a temptation to overactivate the appli-
ance. This may result in pain, anchorage slip and
Provided that the appliance has been correctly perhaps unwanted tilting of the tooth.
adjusted lack of tooth movement is usually due In general, palatal finger springs made to the
to inadequate wear. It is sensible to look for design described are ideal and we favour the
other signs of poor wear before discussing this use of these whenever possible. If the operator
with the patient. Difficulty in handling and has access to a force gauge of the 'Correx' type
inserting the appliance, speech problems, poor (Figure 10.15), it is possible to check the spring
fit, lack of attrition facets on bite planes and an pressure being applied. This may be carried out
absence of marks on the palate at the periphery in the following manner:
of the baseplate - all these point to lack of full-
time wear. Careful questioning of the patient
may elicit that it is left out for meals, at night, Figure 10.15 Correx spring
gauge to measure force
or at school.
applied by springs.
Activation
For a single rooted tooth a force of 30-40 g is
appropriate to produce controlled movement
with minimal tipping. The thickness and length
of the spring will determine the amount of acti-
vation necessary to produce such a force, but a
desirable activation is roughly one-third to one-
half a unit (about 3 or 4 mm). A palatal finger
spring constructed in 0.5 mm wire correctly acti-
vated will deliver the desired force (Figure
10.14). If more activation is attempted the appli-
ance may be difficult to insert correctly. The
chance of the spring being wrongly positioned is
increased and the spring is also more prone to
damage.
A thicker or shorter spring may easily Palatal springs
produce a force thai is too heavy. For example,
if a buccal canine retractor is constructed in The appliance is placed in the mouth with
0.7 mm wire, activation must not be more than a the spring in the correct position. The point
third of the width of the canine to keep the force at the edge of the acrylic from which the
below 40 g. The tooth will quickly move through spring emerges is marked with a wax pencil.
this distance and halt. Unless the patient attends The point on the spring that delivers the
frequently this produces slow movement and force to the tooth should also be marked.