Page 80 - REMOVABLE ORTHODONTIC APPLIANCES

72 Removable Orthodontic Appliances
tooth movement with adjustments at 4-6 danger of anchorage loss, tubes should be
weekly intervals. (Whether one or two appli- soldered to the first molar clasps and the
ances are used, the canines must be retracted anchorage reinforced with headgear. Alterna-
fully before the palatal acrylic is trimmed and tive springs for retraction of the incisors are a
the labial bow activated.) high labial arch with apron spring, a split labial
Stability of overbite reduction depends on bow, self-straightening wires or the extended
the establishment of a stable contact between bow as described in Chapter 3.
upper and lower incisors. If the interincisal
angle (angulation between the long axes of the Retraction of individual incisors
upper and lower incisors) is appreciably greater
than 140 degrees, the overbite will deepen Occasionally, individual incisors have to be
when appliances are discontinued. Only mild retracted. An incisor, which is more labially
class II, division 1 cases should be treated with placed than the others, will show a tendency to
removable appliances. If the skeletal pattern is relapse. To allow for this, the tooth should, if
markedly class II, if the overjet is very large, or possible, be over-corrected. Precise control
if the incisors are not proclined, there is little over individual tooth position is more readily
chance of obtaining good results with remov- obtained with a less flexible bow than may be
able appliances. These patients will require a used for the reduction of a large overjet (Figure
more complex treatment. 8.12).

An appliance to retract the upper incisors An appliance to retract a prominent upper
(Figure 8.11) central incisor
Active component Active component
A Roberts' retractor. A labial bow in 0.7 mm wire, either with
reverse loops (see Figure 3.25, p. 27) or 'U'
Retention loops (see Figure 3.21, p. 25) is recommended.
Clasps on 616. An extended bow can also be used (see Figure
3.27, p. 27).
Anchorage
This is provided principally by the first perma- Retention
nent molars. If space is very short, anchorage Clasps on 6|6.
may be reinforced by extraoral traction applied
via tubes on the molar clasps. Anchorage
Adequate anchorage is provided by the first
Baseplate molars.
A bite plane is required to maintain or produce
overbite reduction. The depth of the bite plane Baseplate
will depend upon the size of overjet. If the over- An anterior bite plane should be used to ensure
bite has already been reduced, the bite plane overbite reduction and to allow full retraction
should be made almost level with the lateral of the incisors.
incisor edges. Bite plane adjustment is
described on p. 38. Soft stainless steel wire Points to note
stops are included to prevent relapse of the Space will, again, need to be provided by the
canine retraction. retraction of the canines. This may be carried
out using palatal springs on the same appliance.
Points to note Over-correction of a labially placed incisor,
Anchorage demands during incisor retraction while desirable, can only be carried out when
are generally less than those during canine the lower incisors permit. Upper incisor irregu-
retraction. Occasionally, problems may be larity may often reflect that of the lower
encountered where there is a strong contrac- incisors and permanent correction of the upper
tion of the lower lip behind the upper incisors incisor positions may not be possible unless the
but a full bite plane to the height of the incisors lowers are also to be aligned. The bow should
will usually prevent this. Where there is a be adjusted later with bayonet bends (Figure