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THE CHILDHOOD PERIOD OF THE PERMANENT TEETH. 263
cusps only have been mentioned because these only are shown
in the available illustration. The lingual cusps, particularly
of the upper molars, play an important part on the same prin-
ciple mentioned for the buccal cusps. This error when these
teeth come into occlusion is the basis of more irregularities of
the teeth than any other one thing. The opportunity for this,
however, is usually found in caries of deciduous molars by
which they have been lost, lost their crowns, or some part of
their mesio-distal breadth, which allows one or the other of the
first molars to stray too far from its normal position in coming
into occlusion with its fellow. Dentists having families of chil-
dren under their care should discover this particular error in
its inception and contrive means for its correction at that time
and prevent the impending irregularity.
Special Functions of the Fiest Permanent Molars.
The first molars have special functions to perform. They
seem to have been so placed and timed in their coming into
position for these special purposes. They come into position,
occluding with each other, just before the shedding of the decid-
uous teeth begins. Normally, the shedding process begins almost
immediately they come into full occlusion. The front part of
the arch is soon broken by the shedding of the deciduous teeth
and these four teeth stand in occlusion, propping the jaws in
the position they should occupy during the shedding of the
deciduous teeth and during the reformation of the arch. They
hold the jaws firmly in the position they should occupy during
the growth and development of the face. In the examination
of a considerable number of cases, it is found that, with the effect
of disease and the irregularities that occur in the absorption of
the roots of the deciduous teeth and their replacement by the
permanent teeth, the support of the jaws is many times almost
completely lost but for the presence of the first molars. They
do much more than this. Accompanying the shedding process
there is a rapid growth of the bones of the jaws and face, making
for the changes of the features from the form in the child and
the modeling of the features of the adult. Particularly the
space from the lower orbital ridge to the crest of the alveolar
process between the teeth is increasing, the depth of the lower
jaw from the crest of the alveolar process to its lower border
is increasing. Together these are lengthening the face from
above downward. At the same time the whole front of the
face is being carried forward, increasing the distance from