Page 12 - REMOVABLE ORTHODONTIC APPLIANCES

4 Removable Orthodontic Appliances
appliance. After that time, appliance treatment
may be considered if there has been insufficient
spontaneous change. Frequently, a removable
appliance may be used in the upper arch when
the lower arch either requires no treatment or
will align spontaneously following premolar
extractions.
If the capacity for spontaneous tooth move-
ment is fully utilized throughout treatment then
the range of cases which can be treated with
removable appliances will be extended and the
standard of results improved.

Active movements
Tipping
Removable appliances act by applying
controlled forces to the crowns of the teeth.
Because only single-point contact is possible,
tooth movement occurs solely by tipping
(Figure 1.4). The fulcrum will usually be about
40% down the length of the root from the apex.
By applying forces of 25-50 g, tipping can be
achieved with the crown moving by about 1 mm
per month. Active removable appliances
should be used only where the teeth can be
tipped into their correct positions.
Tipping can either be in a mesio-distal direc-
tion (in the line of the arch) or in a bucco-
Figure 1.3 Relief of crowding in the lower arch in palatal direction. The key feature is the
advance of the upper arch can allow for the position of the apex of the tooth before move-
establishment of a class I molar relationship. ment. When the apex is well positioned, a tooth
will usually respond satisfactorily to removable
appliance treatment provided that the direction
of movement tends to upright it. A tooth which
closure. Unfortunately, the readiness with
which such movement occurs can exacerbate
any anchorage loss produced by injudicious
appliance use.

Timing of spontaneous movement
Spontaneous movement takes place while the
patient is growing and may occur most rapidly
during the pubertal growth spurt, when there is
a considerable amount of bone development
and remodelling. From a practical point of
view, the majority of labio-lingual and upright-
ing movements will take place within a 6-month
period following extractions. Where space is
obviously excessive it may be wise to allow Figure 1.4 Application of a force to the crown of the
some initial closure before fitting the first tooth results in a tipping movement.