902H
Fig. 14.3 (a) Class I occlusion with crowding of the lateral incisors in an 8 1/2-year
old patient, before extraction of primary canines. (b) Aged 10 1/2-, 6 months before
extraction of first premolars. Upper canines palpable in buccal sulcus, lower canines
crowded buccally. (c) Aged 13⎯excess space in lower arch. (d) Aged 15⎯upper
spaces closed, lower spaces reducing. (Photos courtesy of Mr T. G. Bennett.)
14.3.3 Enforced extraction of primary teeth
The main complication of the enforced extraction of poor quality primary teeth is
mesial drift of the teeth distal to the extraction space, causing crowding of the
permanent successors. Mesial drift is greatest where there is a tendency to crowding,
and it also becomes greater the more distal the tooth to be extracted is. It is greater in
the upper arch than in the lower, as the upper permanent molars are distally inclined
on eruption and readily move mesially by uprighting, whereas the lower permanent
molars are mesially inclined on eruption and move forward less readily, but tilt
mesially as they do so.
Extraction of primary incisors usually causes virtually no drifting of other teeth, but if
done very early may delay the eruption of the permanent incisors. (Loss of a
permanent incisor is a very different matter⎯see 903HSection 14.7.1.)
Extraction of a primary canine causes some mesial drift of the buccal segment,
depending upon the degree of crowding. There is also drift of the incisors into the
space, which causes a centreline shift towards the extraction site. This should be
prevented by balancing the extraction with loss of the contralateral canine. In the
same way the extraction of a primary first molar allows mesial drift of the teeth distal
to it, more than with the loss of a canine, and there may also be some effect on the
centreline. Where the distribution of caries indicates loss of a primary canine on one
side and a primary first molar on the other, these extractions can be regarded as
balancing each other reasonably well and the contralateral teeth can be retained.