Page 46 - REMOVABLE ORTHODONTIC APPLIANCES

38 Removable Orthodontic Appliances
clinicians will build up the bite plane by a small
amount every few visits as long as overbite
reduction is needed. Most children, however,
can tolerate a greater opening and this means
that greater increments can be added less
frequently. If the bite plane is constructed to
half the incisor height on the first appliance and
to full incisor height on the second, few, if any,
chairside increments will be required. It is wise
to wait until the posterior teeth have regained
contact before undermining the bite plane to
permit overjet reduction. In adults, overbite
reduction is difficult to achieve and will take
place slowly, so it is important to increase the
thickness of the bite plane slowly with progres-
sive additions of cold-cured acrylic as the over-
bite reduces. Figure 5.4 Trimming an anterior bite plane to allow
overjet reduction. The fitting surface is progressively
trimmed away to allow the upper incisors to be
retracted while the lower incisors are still in contact
with the bite plane. The leading edge of the bite
Anterior bite plane adjustment and plane is trimmed in a smooth curve.
overjet reduction
Before the upper incisors can be retracted to
reduce an overjet the anterior bite plane will
need to be trimmed away from these teeth. It Posterior bite planes
will also require later progressive, careful Posterior bite planes should be adjusted at the
reduction so that the lower incisors maintain time of fitting so that there is an even contact
their contact with it until the overjet is almost with the posterior teeth on both sides of the
corrected. These teeth will otherwise re-erupt arch. It is almost inevitable that some adjust-
and the overbite increase again. The acrylic ment of the occlusal surface will be necessary.
. should first be trimmed vertical to the bite This should be checked with articulating paper
plane, by the required amount. It is helpful to - ensuring that the patient closes in centric - so
mark this with a wax pencil on the bite plane - that the occlusal surface of the bite plane is
trimming up to, but not beyond the line. The faceted to accept the opposing teeth in the
acrylic should be trimmed back only as far as centric relationship. If an anterior crossbite is
necessary to permit the tooth movement being corrected the bite plane needs only to be
expected by the next visit. Excess trimming of sufficiently thick to disengage the occlusion on
acrylic may encourage the patient to posture the anterior teeth. Quite commonly the poste-
the mandible forwards in front of the bite plane rior aspect of a bite plane may perforate
and any achieved overbite reduction will be because the acrylic is thin. Once the crossbite is
lost. If the bite plane has not been made suffi- corrected, the molar capping should be reduced
ciently high then contact with the lower incisors or removed. If there is concern that the sudden
will quickly be eliminated as the acrylic is cut removal of bite planes may allow the patient to
away (Figure 5.4) and to rebuild it sufficiently posture the mandible to the original position
at the chairside is tedious. When the acrylic has then reduction may be carried out over two or
been cut back sufficiently, it should be under- three consecutive appointments.
mined to clear the palatal surfaces of the
incisors and the palatal mucosa. If this is done
before overbite reduction has been completed
the appliance may rock when the patient Further reading
occludes. The problem can be avoided by
ensuring that the overbite is reduced Cousins. A.J.P., Brown. W.A.B.. Harkness, E.M. (1969) An
adequately before incisor retraction investigation into the effect of the maxillary biteplate on
incisor
lower
teeth.
of
Transactions
the
ihe
height
of
commences.
BSSO, 55: 105-109