Page 87 - REMOVABLE ORTHODONTIC APPLIANCES

Class III malocclusions 79

Figure 9.2 (a) A unilateral crossbite with a displacement of the mandible results in a centre-line shift, (b)
Examination of the patient in the non-displaced position may demonstrate an underlying mild class III skeletal
base.

Overbite and overjet reverts to closure in centric and the prog-
nathism is apparent (Figure 9.2). A unilateral
In the absence of a displacing activity and when
the patient cannot readily obtain an edge-to- crossbite with two or more incisors in reversed
is
be
likely
too
overjet
to
correct
difficult
to
edge incisor relationship, successful correction
is unlikely with removable appliances. Even with removable appliances.
when the patient is able to bite edge-to-edge, A bilateral crossbite normally has to be
the prognosis will depend on the incisor incli- accepted and may be an indication of an under-
nation and the amount of overbite present. lying skeletal pattern, which is too severe to
Where the overbite is reduced, the prospect for respond to simple treatment.
a stable long-term correction may be poor even
if there is a mandibular displacement.
If the incisor inclination already compensates Age factors
for the class III skeletal pattern (with the upper If a reversed overjet is present in the estab-
incisors proclined and the lower incisors retro- lished permanent dentition the considerations
clined), further labial movement of the upper of skeletal pattern, incisor angulation and
incisors will often produce a traumatic relation- displacement will be particularly important. In
ship with the lower incisors. In such a situation the pre-pubertal patient the possibility of
it is unlikely that a stable incisor relationship further mandibular growth must be an impor-
can be achieved by orthodontic treatment tant consideration.
alone. A single, crowded, upper lateral incisor in
crossbite, in the established dentition, may be
difficult to correct with a removable appliance
Buccal crossbite
alone as these palatally placed incisors are
A unilateral crossbite can disguise an underly- usually associated with a centre-line shift
ing class III skeletal pattern because the (Figure 9.3).
displacement causes the mandible to move Upper lateral incisors in lingual occlusion
slightly to one side on closure producing an and with an increased overbite are frequently
effective shortening of its length. When the associated with an anterior displacement of the
displacement is eliminated the mandible mandible on closure, due to a premature