Page 68 - REMOVABLE ORTHODONTIC APPLIANCES

60 Removable Orthodontic Appliances
started to erupt. An attempt to move both first The lower removable sectional
and second permanent molars distally is likely appliance
to procline the lower incisors and, following
removal of the appliance, they will drop back Crowding and irregularity of the lower incisors
into muscle balance and produce secondary present a special problem in orthodontics. A
crowding. Occasionally, it may be necessary to patient may attend with a good occlusion but
remove the second permanent molar in order with irregularity of the mandibular anterior
to move the first molar distally, but the third teeth, which is unacceptable. Such a patient
molar must be present and in a favourable posi- may have had no previous orthodontic treat-
tion. ment or have had a course of treatment some
years previously, perhaps including extractions.
The problem occurs commonly in young adults
An appliance to move a lower first and in these circumstances the sectional remov-
permanent molar distally (Figure 7.17) able appliance described by Barrer (1975) may
Active component be useful. Lower incisors have a mean collec-
tive mesio-distal width of 22 mm (± 1.4 mm).
A screw with a single guide pin.
The enamel thickness of an incisor at the
Retention contact point is 0.75 mm. The removal of 50%
Clasps on 64|46 or clasps on 6|6 and a labial of the enamel from each contact point will
bow. create 3 mm of space in the incisor region. Such
space may be used to effect incisor alignment
Baseplate provided that crowding is not too great and that
any rotations are minimal.
This is split at the screw.
Anchorage Enamel stripping
Provided by the teeth anterior to the second
premolar. This may be carried out before or after appli-
ance construction, but is best done beforehand
Points to note if the appliance can be supplied within a few
As indicated above, anchorage may be a prob- days. Enamel removal may be carried out in
lem but it is not practicable to provide support several ways. Because the contact points will be
from outside the arch for a lower removable tight initially it should be started with metal-
appliance. To minimize the forces on the backed abrasive strips. When adequate access
anchorage, the screw should be activated by has been gained, further enamel may be
only one quarter-turn each week. removed either in the same manner or with a

Figure 7.17 An appliance to move a 6|
distally. Adams' clasps on 6|6 (0.7 mm) and
labial bow (0.7 mm). A carefully sited screw.