Page 35 - REMOVABLE ORTHODONTIC APPLIANCES

Active components 27
Figure 3.25 A reverse loop labial bow
(0.7 mm).

Figure 3.26 Adjustment of a reverse loop labial Figure 3.27 An extended labial bow (0.7 mm).
bow. When the pliers compress the loop at A, the
anterior part of the bow drops down and a
compensating bend needs to be made at B.

enlarged loops (Figure 3.27). This bow is a Nevertheless, there are certain situations in
useful alternative to the Roberts' retractor for which screws are very useful.
reduction of an overjet and it is also suitable for Many types of screw are commercially
the alignment of irregular incisors. Due to the available for use in removable appliances.
size of the loops, it may be less comfortable for Desirable features in a screw are adequate
the patient to wear. travel, stability and minimal bulk (Haynes and
Jackson, 1962). Screws can be used for many
tooth movements, but they add to the expense
Adjustment
of an appliance while making it more bulky.
The bow must be adjusted with care to avoid Adjustment is normally carried out once or
trauma to the buccal mucosa. twice weekly by the patient. We recommend
screws only in those few situations where
springs would be unsatisfactory: for example,
Screws where the teeth to be moved are required for
retention of the appliance (see Figuie 9.9
An alternative method of providing a force is to p. 84). Single and double guide pin screws are
use a screw as an integral part of the removable available (Figure 3.28). The latter are more
appliance. The screw normally transmits its stable but the former is useful where space is
force by means of the acrylic, which comes in limited. Problems can occur with screws. Some
contact with the teeth. The patient usually acti- tend to turn back under load. If the appliance
vates a screw once or twice a week. A fairly is left out it may not be possible for the patient
high force is generated but is intermittent. to re-insert it and treatment may thus be