Page 56 - REMOVABLE ORTHODONTIC APPLIANCES

48 Removable Orthodontic Appliances
length while monitoring the spontaneous screw is that it can be positioned closer to the
improvement of teeth adjacent to the extrac- teeth in crossbite and, by sectioning the
tion site. This applies particularly to maxillary acrylic baseplate into greater and lesser
canines, mandibular canines and mandibular portions, the anchorage balance can be
incisors. It is often only necessary to maintain altered to give differential expansion.
space in the upper arch because, provided the Molar occlusal covering is indicated when
appliance does not disengage the teeth, the there is a significant displacement of the
occlusal relationship of the molars should mandible and is frequently used when cross-
prevent the slower rate of spontaneous space bite correction is undertaken in an estab-
closure in the lower arch. A suitable appliance lished dentition.
can be simple in design because the palatal • Occlusal tooth movement - Where it is
acrylic is the effective component in maintain- necessary to apply direct traction to a
ing arch length and no active springs are partially erupted tooth a removable appli-
required. Good retention might be provided by ance is the method of choice, since it takes
Adams' clasps on posterior teeth and an full advantage of the vertical anchorage
Adams' clasp or Southend clasp on the incisors. provided by the palatal vault through its
Where passive space maintenance is suffi- close contact with the acrylic baseplate. In
cient, night-time wear will be effective. This the early mixed dentition, the eruption of
offers a significant advantage over the fixed central and lateral incisors can be delayed as
appliance alternatives such as the soldered or a result of an interfering factor such as a
removable palatal arch attached to molar supernumerary tooth, which has to be
bands, which must inevitably be in place full removed surgically. More commonly, an
time over an extended period. impacted maxillary canine has to be brought
Lower removable space maintainers can be into the line of the arch following surgical
similarly constructed but are less convenient to exposure. In either event a suitable traction
use than a cemented lingual arch, which may be point, such as a bonded hook or bracket,
a better choice. needs to be provided. In such cases it is usual
to continue removable appliance therapy
until the tooth is at approximately the same
occlusal level as the naturally erupting teeth.
Active tooth movement in Class 1 A fixed appliance can then be used for the
cases detailed tooth movements needed to
complete treatment.
• Mesio-distal tooth movement - This is
commonly required to relieve crowding of • Opening space - In the early mixed dentition
canines or incisors and is a movement that is it is sometimes necessary to recreate suffi-
most satisfactorily carried out with remov- cient space to allow the natural eruption of
able appliances. an incisor which has been delayed for some
• Bucco-palatal movement - Buccal or palatal reason. The principles of such treatment
movement of crowded teeth is satisfactorily involve the removal of any impeding factor
achieved provided that there is sufficient (such as a supernumerary tooth) and the
space in the arch. provision of generous space into which the
• Posterior crossbites - Where there is a tooth can erupt. Since the encroaching teeth
unilateral crossbite in the molar or premolar are generally tipped towards the space it is
region a removable appliance can be very often appropriate to enlarge that space by
effective in eliminating any associated tilting them into an upright position using
mandibular displacement on closure, while springs on a removable appliance. Such
achieving the necessary maxillary expansion treatment is often needed in the early mixed
for correction. Such an appliance can use dentition, when permanent buccal teeth are
either a spring or a screw as an active compo- not available for the placement of fixed
nent. The most appropriate spring in these appliances. Patients in this age range often
circumstances will be the coffin spring with cope better with a removable appliance than
the apphance divided sagittally into halves. with a fixed appliance. Furthermore, any
Screws may be similarly incorporated in the complete treatment with fixed appliances
mid-line of an appliance. The advantage of a will usually have to be deferred for some