- The behaviour of the lower second molars is fairly unpredictable following loss of
lower first permanent molars and is greatly influenced by the timing of the
extractions.
In general, therefore, first permanent molars are only extracted if their long-term
prognosis is felt to be poor, and the orthodontic management of these extractions aims
to minimize disruption of the developing dentition. Where the loss of one or more
first molars is necessary in the mixed dentition, the management of the extractions
depends on whether or not the patient is likely to have active treatment with
orthodontic appliances in the future⎯often a difficult judgement to make.
A panoramic radiograph must be taken to confirm the presence of all permanent teeth
(except for third molars) before finalizing the extractions. The following discussion
assumes the presence of all permanent teeth⎯if a premolar is congenitally absent then
the first molar in that quadrant should be saved if possible.
Extraction of first permanent molars where no orthodontic treatment is planned
The objective is to minimize disruption of the occlusion. Following the extraction of a
first molar, the paths of eruption of adjacent unerupted teeth alter, and erupted
adjacent and opposing teeth also start to drift. Many of these changes are unhelpful,
but some can be used to advantage with careful planning.
In general, the most obvious change is mesial drift of the second molar, especially in
the upper arch. However, in the lower arch some distal movement of premolars and
canines may also be expected, especially where the arch is crowded. The extraction of
first molars can be a convenient way of relieving pre-molar crowding, especially in
the lower arch. In the lower arch the timing of the extraction is important. If carried
out very early the unerupted lower second pre-molar migrates distally, sometimes
leaving a space between the first and second premolars if the arch is uncrowded (907HFig.
14.5). If carried out late, as or after the lower second molars erupts, that tooth tilts
mesially under occlusal forces and can cause an occlusal interference⎯especially if
the opposing upper first molar overerupts into the lower extraction space (908HFig. 14.6
(a) and (b)). There is often residual space mesial to the tilted second molar and this
poor relationship with the second premolar may cause a stagnation area. These
unwanted effects can be minimized in two ways:
- Extraction of the upper first molar⎯this eliminates the problem of overeruption of
the opposing first molar, and removes the occlusal contact which exaggerates mesial
tilting of the lower second molar (909HFig. 14.7 (a) and (b)). - Careful timing of the extractions⎯ideally when the bifurcation of the roots of the
lower second molar is starting to calcify, usually at about 8 1/2 - 9 1/2 years of age
(910HFig. 14.8 (a) and (b)).
In the upper arch the behaviour of the second molar is more predictable, although
timing is still important. The tendency to mesial drift is much greater than in the lower
arch, and there is almost no distal drift of the upper premolars. If the upper first molar
is extracted early, the unerupted second molar migrates mesially so that it erupts into