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CORI^l'.CTION OF DENTAL IRREGULARITIES. I 55

nicnt. The cause is usually the lack of aKcolar development
in the anterior portion of the mouth, sometimes accompanied
with an excessive growth in the molar region.
Treatment.—When the deformity is slight it may be cor-
rected by grinding off all the antagonizing points from the
posterior teeth, thus shortening the bite, bringing the an-
terior teeth cl(^ser together. If the third molars were in
position and adding to the trouble they should be extracted.
Then, if necessary, one or more of the remaining molar
teeth upon either side of the mouth (those in the poorest
condition to be selected) may be devitalized, ground down
beyond the point necessary, and then covered with gold
crowns.
\\'here considerable grinding upon vital teeth is done and
the exposed dentine becomes quite sensitive, it may be ob-
tunded by a repeated application of either chlorid of zinc
or nitrate of silver.
"Retention and Retaining Devices.—The tendency of
teeth which have been regulated is to return to their former
malposition. Retaining devices are therefore designed to
hold the teeth in their new^ position until they become per-
manently so fixed by nature. Fixtures of this nature should
be made as delicate and inconspicuous as possible, consistent
with perfect support. The force or antagonism exerted to
o^•ercome the tendency to a backward mo^'ement is not very
great, but it must be constant. That is a retaining appli-
ance should, as a rule, be made stationary by carefully fitted
and cemented bands. It should also be made with as little
bulk as possible that it may more readily be kept clean by
the patient, and should be inspected occasionally by the
dentist to see that it is kept clean, that no injury may come
to the teeth.
The time required for mechanical retention varies accord-
ing to the age of the patient, the movements which have