Page 117 - REMOVABLE ORTHODONTIC APPLIANCES

Problem cases 109
segment relationship due to the discrepancy in extracted and the premolars retracted to
the number of teeth in each arch. relieve crowding. Once this is completed another
appliance will be required, clasping the premo-
lars and the second molar, while the opposite
Non-vital teeth first molar is extracted and further tooth move-
ment carried out. This will, inevitably, lengthen
Non-vital teeth may be moved orthodontically, treatment.
provided that they have been adequately root Where there is marked crowding or a signifi-
filled and have a reasonable root length. The cant overjet to be reduced, it may be more
patient and parents should be warned that it is sensible to extract the upper first molars, allow
possible for such teeth to become excessively spontaneous space closure and consider further
mobile or to resorb during treatment. Gentle extractions at a later stage.
forces must be used; a check on tooth mobility
should be made regularly and radiographs
taken if necessary. Centre-line shift
Where a tooth is traumatized but remains
vital, orthodontic movement may cause loss of A shift of the centre-line may occur following
vitality. Following a history of trauma the unilateral early loss of a deciduous tooth,
child's parents should be warned of this possi- whether this has occurred spontaneously or as
bility before orthodontic treatment the result of enforced extraction. Unilateral
commences. loss of a permanent tooth, for example a Jfirst
molar, may also produce a centre-line shift.
This tends to be more noticeable in the upper
Enforced extractions arch, but is just as significant in the lower arch.
Maintenance of a correct centre-line in the
The need to extract teeth as the result of caries lower arch is important if a satisfactory buccal
has reduced greatly in recent years. First molars intercuspation is to be achieved at the end of
may still present problems on occasion either treatment. Balancing extractions should be
due to caries or hypoplasia. considered, especially in the lower arch, if there
Provided that all unerupted premolars and is an element of crowding. In the upper arch,
second molars are present, the early extraction correction of a shifted centre-line cannot be
of lower first molars can give good results in a achieved with a removable appliance.
crowded case. Usually, such extractions will An apparent shift of the lower centre-line may
demand compensating upper first molar extrac- be due to a displacing activity of the mandible
tions to avoid the over-eruption of the upper associated with a buccal crossbite. The initial
first molar, which might interfere with space treatment will usually involve elimination of the
closure in the lower arch. In the established displacing activity by means of upper arch
dentition, extraction of the lower first molars expansion before the extraction of any perma-
will invariably require the use of a fixed appli- nent teeth is considered (see Chapter 7).
ance to achieve satisfactory space closure and
alignment.
In the upper arch, a limited amount of tooth Unilateral crowding
movement can be achieved following the
extraction of upper first molars. This does not Occasionally, marked crowding may be present
give sufficient room to reduce an overjet. In a on one side of the arch. If this is associated with
class I case, movement of the premolars into a centre-line shift then unilateral extraction
the first molar extraction site can give space to may allow the shift to worsen, especially in a
align canines. growing child. Unilateral extraction can be
Where the upper first molars must be considered in an established dentition or in an
extracted before the eruption of second molars adult.
it may be difficult to provide adequate reten- Where unilateral crowding is present in the
tion. The problem may be overcome by retain- absence of a centre-line shift then premolar
ing one of the first molars temporarily to accept extractions may be considered at the site of
a clasp, while the opposite first molar is crowding.