Page 760 - My FlipBook

758 ORTHODONTIA AS AN OPERATIVE PROCEDURE.

The semi-V of Dr. Talbot's classification is one in which the causes
named have operated on one side only of the arch. Fig. 748 shows a
serai-V arch due to the last cause
^
mentioned.
{d) The V shape assumed by
the central incisors may be due to
lack of development of the inter-
FiG. 749.

Semi-V-shaped arch. Apices of roots too near together.

maxillary bone at the median suture. This would bring the apices of
the roots of these teeth nearer each other than is normal. As the teeth
erupt they may come in contact with each other above the gum line, but
be separated from each other at the mesio-incisal angles. If they are
now crowded together by the lateral incisors, or if an attempt be made
to draw them together by means of a rubber band or ligatures, they will
roll upon each other in such a manner that when the mesio-incisal
angles touch they have also assumed a V shape with the apex of the
V pointing forward.
Conversely, when a V shape of tiiis kind is reduced by double rota-
tion,^ the teeth will assume the position shown in Fig. 749.
The old theory that it was due to mouth-breathing is no longer ten-
able, as it has been demonstrated that the pressure of the muscles upon
the teeth in such action is not sufficient to cause this deformity. This
has been proved by examination of a great number of children in schools
and public institutions.
Ti^eatment.—The treatment of the pointed arch depends on the
relation in size between the jaw and teeth. If the teeth are not too
large for the jaw, and the deformity consists in the flattening of the
sides of the arch, the operation is comparatively simple. If pressure
be brought to bear on the summit or point of the arch while the base on
each side is fixed, the sides will spring outward like an arch of whale-
bone. (See Fig. 750.)
Many pointed arches are also cases of upper protrusion, and will be
treated of under that division.
One of the oldest appliances and a very satisfactory one is shown in
^ See Class 3.