Page 50 - REMOVABLE ORTHODONTIC APPLIANCES

42 Removable Orthodontic Appliances

Figure 6.5' (a) When only intraoral anchorage is used, canine retraction results in forward movement of the
anchor teeth, (b) Intraoral anchorage can be reinforced with extraoral thus limiting forward movement of the
posterior teeth during canine retraction.

if necessary. When anchorage is solely intraoral while upper canines are being retracted,
it is very common for some movement of the provides a simple and reliable way of checking
anchor teeth to occur. This may be acceptable in anchorage stability. This measurement must be
some situations but, if space is critical, it may be taken with the mandible in a fully retruded posi-
wise to plan for extraoral anchorage from the tion on each occasion. It is easy to be misled if
start (Figure 6.5). If this is not done, it is very the patient progressively postures the mandible
tempting to delay anchorage reinforcement forwards to maintain occlusal relationships.
until excessive space has been lost and must A sure sign that anchorage loss is occurring
then be regained - a tedious exercise for patient in the upper arch is a tendency for a buccal
and operator alike. crossbite to develop. If the upper molars are
Assessment of anchorage stability can be diffi- brought forward while the transpalatal distance
cult. Measurements taken to other teeth in the between them is maintained by the baseplate,
same arch are frequently misleading because all they will come to oppose a narrower part of the
teeth contacting the baseplate may move by an lower arch.
equal amount leaving their relationship to each
other unchanged. Reference to the opposite
arch is more reliable, but here, too, teeth may Anchorage control
move if premolars have been extracted. The
most reliable base for measurement is the lower If anchorage loss is detected action must be
labial segment, which should be stable in the taken immediately. The forces being supported
intact lower arch. If lower premolars have been by the anchorage need to be checked first. If too
extracted, however, imbricated lower incisors many teeth are being moved at the one time, or
may start to align and the most labially placed it excessive forces are being used, this must be
incisor is likely to drop back. This will be shown remedied. Attention should then be paid to
as a slight increase in overjet and must be reinforcing the anchorage itself. The only effec-
allowed for. Provided the baseplate contacts all tive way of improving anchorage is to supple-
the teeth that are not to be moved a change in ment it with extraoral force. If headgear is
the position of any of these teeth relative to a already fitted the elastic traction may need to be
stable point in the lower arch gives a warning of strengthened. If this is already adequate then
anchorage loss. A record of the overjet, kept the hours of wear may need to be increased.