Page 103 - REMOVABLE ORTHODONTIC APPLIANCES

Chairside management 95
tip of the upper left central incisor. When this improved. It is important to ask to see the
routine must be changed, perhaps because the diary at each visit and to give encourage-
tooth in question is fractured or lost, then the ment or praise in order to reinforce the
position from which the measurements are patient's efforts. Where cooperation is not
taken should be recorded carefully in the notes. adequate, all that can be done is to empha-
size to the patient (and parent) that failure
to wear the appliance as instructed can only
Anchorage delay treatment and prejudice the result.
• Where marked anchorage loss has occurred,
Newton's third law of motion tells us that every changes in the relationship of the two arches
force has an equal and opposite reaction. When will become noticeable. If the upper teeth
teeth are being moved the reactive force will be are brought forward during the canine
transmitted through the appliance and will retraction they will retain the previous arch-
affect other teeth which are themselves capable width because they are held by the base-
of movement. Measurements such as those plate. They will therefore tend to become
described above indicate that movement is buccally placed.
taking place but do not show that only the
intended teeth are moving. It is important to When unwanted movement is discovered,
take further measurements at each visit to corrective action should be taken at once. If the
confirm that anchorage loss is not occurring. active components are exerting too great a
force this must be reduced. Space requirements
• Where only one arch is being treated it is should be reassessed. If there is space to spare
usually easy to use the other arch as a refer- some loss of anchorage may be accepted. If
ence. In the case of upper canine retraction space is short, however, anchorage reinforce-
a measurement of overjet should be taken ment, usually with headgear, is essential.
(Figure 10.12) and any increase in this is
usually a warning that anchorage is being
lost (Figure 10.13). The molar relationship Lack of satisfactory progress
will also become more class II. When lower
arch extractions have been carried out Is the tooth free to move?
assessment can become more difficult.
If the baseplate is in contact with the tooth it
• Imbricated lower incisors can align sponta-
neously and if the overjet was measured should be cut away sufficiently to ensure that
from a tooth which had been prominent it further obstruction does not occur. Where the
will appear to increase as this alignment obstruction is due to occlusal interference the
occurs. bite plane may need to be thickened by the
of
cold-cured
certain
• Where headgear is being worn it is useful to addition unerupted tooth acrylic. Make root has
that
an
or
retained
ask the patient to keep a diary of wear. By
giving the patient a target number of hours not been overlooked.
to be achieved per week, motivation can be
Has the correct force been applied?
Check that a spring is located correctly and on
the right side of the tooth when the patient
inserts the appliance. Make sure that the spring
is adequately activated. Where a screw-plate is
being used the patient may be adjusting the
screw incorrectly. The operator can ask the
patient to demonstrate turning and the screw
can be turned back to check that the number of
turns corresponds with that expected.
The use of heavy pressures will cause hyalin-
ization within the periodontal ligament and
Figure 10.12 Measurement of overjet using a delay resorption, so light pressure should be
millimetre steel rule. maintained and the patient should be warned