Page 78 - REMOVABLE ORTHODONTIC APPLIANCES

70 Removable Orthodontic Appliances
3. Retention by extraction (usually of the first premolars) or
by retraction of the buccal segments. Remov-
The reduced overjet requires retention which is
best provided by a purpose-made retainer with able appliances are suitable for the retraction of
Retraction
mesially
the
inclined
of
canines.
cribs on upper first molars and a 'U' loop labial
until the canines have
bow. The Roberts' retractor is not ideal for reten- incisors must be delayed anchorage will be over-
corrected
been
or else
tion because it is too flexible and can, over a loaded. For a canine in the line of the arch a
period of time, become distorted. When a
buccal
best,
but
is
spring
reverse loop labial bow is being used for overjet palatal for a buccally crowded a tooth. spring is
better
reduction, this may be used for a retention phase.
Provided that the lower incisors and canines
are well aligned the upper canines should be
Extraoral anchorage retracted into a class I relationship with the
lowers. If the canines are to be retracted by more
If the molars are not class I at the outset of a four than half a tooth-width then extraoral support
premolar extraction case extraoral support must must be considered. Where a class II skeletal
be considered. The use of extraoral force pattern precludes the establishment of a normal
supports the molars during canine retraction and incisor relationship (i.e. if a residual overjet is to
aids the achievement of a class I molar relation- be accepted or if the upper incisors will be retro-
ship. Sometimes it will only be needed during clined after retraction) the canines may not have
canine retraction; sometimes through the entire to be moved so far. If slight lower incisor crowd-
treatment. The choice will depend upon the ing is to be accepted, the upper canines need to
severity of the problem and clinical judgement be retracted further unless a residual overjet or
must be used in the management of each case. upper incisor crowding is to be accepted.
Where first premolars are extracted from the
upper arch alone there should be a class II
molar relationship at the end of the treatment.
Extraoral support will be required only if the An appliance to retract upper canines
molar relationship was originally a half-unit (Figure 8.10)
class II or more. Active components
Where the canines are in the line of the arch,
palatal cantilever springs, boxed and guarded,
Canine retraction
should be used. Where a canine must be moved
Before the overjet can be reduced and the palatally as well as distally a palatal spring is
incisors aligned the upper canines must be not suitable and a buccal spring is necessary in
retracted. Space can be provided for this either order to engage the tooth correctly and to

Figure 8.10 An appliance to retract
upper canines. Palatal cantilever springs
(0.5 mm) boxed and guarded. Southend
clasp (0.7 mm). Adams' clasp (0.7 mm). A
flat anterior bite plane.