Page 83 - REMOVABLE ORTHODONTIC APPLIANCES

Class II malocclusions 75

Figure 8.15 An appliance to move upper buccal segments distally. The extraoral bow is embedded into the
acrylic of the appliance. A coffin spring (1.25 mnni) is available for expansion.

Baseplate facebow directly, enabling the molars to be
This is normally trimmed away from behind the moved distally with extraoral force. The inner
upper incisors, but is split in the mid-line to arch of the facebow should be expanded
permit compensating expansion. slightly to provide arch-width correction and
the outer arms should be directed upwards and
Points to note backwards and attached to a safety headgear.
To achieve satisfactory buccal segment move- The molars may become slightly mobile and
ment the headgear needs to be worn for a mini- care should be taken that they are not extruded
mum of 14 hours each day - a longer period than by a downward component force from the face-
would be needed to support a screw-plate. Some bow.
overjet reduction may occur at the same time. It is common to find that the premolars follow
The mid-line screw should be adjusted by the the molars distally due to the effect of the
operator so that the buccal segments diverge as transeptal fibres. If this does not occur a remov-
they move distally, preserving the transverse able appliance can be fitted over the molar
arch relationship and avoiding the creation of a bands once these teeth are in a class I relation-
crossbite. One quarter turn every 4-6 weeks is ship so that premolars and/or canines can be
usually adequate. Alternatively, if a coffin retracted with palatal finger springs. A final
spring is used, this will require expansion by the appliance can also be clipped over the molar
operator at the routine visits. The correction of bands so that extraoral support can, if neces-
an existing crossbite requires more expansion sary, be continued during overjet reduction.
so a mid-line screw should be used and can be
adjusted weekly by the patient.
Because the facebow is An appliance to facilitate distal movement
integral with the of upper molars with bands and extraoral
appliance, this is one of the safest ways of traction (Figure 8.16)
applying extraoral force to the upper arch. Active components
Palatal springs in 6 mm wire can engage both
Bands on first molars
upper first molars to support the distal force
Bands may be placed on upper first molars with applied by the facebow directly to the molar
buccal tubes which accept the inner arms of the bands.