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P. 699
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ETIOLOGY OF DENTAL IRREGULARITIES. 697
The habit of sucking the finger or lip may cause protrusion of either
jaw according to the position of tlie finger or lip.
While thumb-sucking sometimes causes the irregularities mentioned,
it is not a frequent cause, and it is a singular fact that the habit does
not cause irregularity of the deciduous teeth.
. The habit of moutli-b reathing , whether owing to nasal obstructions
or not, may cause lack of anterior occlusion—see (e), page 786—or
apparent lower protrusion—see (t), page 774.
(/) Other Causes of Irregularity. Obstruction of the nasal cavity
by a deflected septum, enlarged turbinate bones, polypi, adenoid growths
in the nasopharynx, enlarged tonsils, or any other cause, by preventing
free circulation of air through the nasal cavity, may be the cause of a
lack of development of the frontal, sphenoidal, ethmoidal, and maxil-
lary bones. This lack of development may produce a high and con-
tracted vault, with a narrow and small arch and consequent crowding
of the teeth into various irregularities.
Lack of development of the intermaxillary bone may cause (a) a pointed
arch (page 757), (6) lack of anterior occlusion (page 786), or (c) prom-
inent canines and depressed laterals—see («), page 745.
Disparity in size betiveen the teeth and the jaw may be due to either
of two widely different causes, and yet produce several similar irreg-
ularities.
(1) This disparity in size may be due to teeth too large for the jaw
(indirect heredity — page 690).
(2) It may be due to premature loss of deciduous second molars and
a forward movement of the permanent first molars, thus shortening the
arch and making it too small for the ten teeth that are to occupv it.
The result may be
(a) Prominent canines and depressed laterals (Class 7, page 745).
(6) Pointed arch (Class 8, page 757).
(c) Upper protrusion (Class 9, page 760).
(d) Constricted arch (Class 12, page 784).
(e) Lower protrusion (Class 10, page 773).
The same condition in both jaws at once may cause similar irregu-
larities in both jaws. One of the most notable of these is double pro-
trusion (Class 11, page 782).
Loss of the deciduous second molar on one side may cause anv of
these irregularities on that side only, such as a semi-constricted or
semi-pointed arch.
Chang-es in Surrounding- Tissues when Teeth are Moved.
1. Resorption axd Deposition.—When a single tooth is moved in
any direction, there is first a compression of the soft and then of the hard
tissues in front of the tooth, and at the same time a stretching of the
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ETIOLOGY OF DENTAL IRREGULARITIES. 697
The habit of sucking the finger or lip may cause protrusion of either
jaw according to the position of tlie finger or lip.
While thumb-sucking sometimes causes the irregularities mentioned,
it is not a frequent cause, and it is a singular fact that the habit does
not cause irregularity of the deciduous teeth.
. The habit of moutli-b reathing , whether owing to nasal obstructions
or not, may cause lack of anterior occlusion—see (e), page 786—or
apparent lower protrusion—see (t), page 774.
(/) Other Causes of Irregularity. Obstruction of the nasal cavity
by a deflected septum, enlarged turbinate bones, polypi, adenoid growths
in the nasopharynx, enlarged tonsils, or any other cause, by preventing
free circulation of air through the nasal cavity, may be the cause of a
lack of development of the frontal, sphenoidal, ethmoidal, and maxil-
lary bones. This lack of development may produce a high and con-
tracted vault, with a narrow and small arch and consequent crowding
of the teeth into various irregularities.
Lack of development of the intermaxillary bone may cause (a) a pointed
arch (page 757), (6) lack of anterior occlusion (page 786), or (c) prom-
inent canines and depressed laterals—see («), page 745.
Disparity in size betiveen the teeth and the jaw may be due to either
of two widely different causes, and yet produce several similar irreg-
ularities.
(1) This disparity in size may be due to teeth too large for the jaw
(indirect heredity — page 690).
(2) It may be due to premature loss of deciduous second molars and
a forward movement of the permanent first molars, thus shortening the
arch and making it too small for the ten teeth that are to occupv it.
The result may be
(a) Prominent canines and depressed laterals (Class 7, page 745).
(6) Pointed arch (Class 8, page 757).
(c) Upper protrusion (Class 9, page 760).
(d) Constricted arch (Class 12, page 784).
(e) Lower protrusion (Class 10, page 773).
The same condition in both jaws at once may cause similar irregu-
larities in both jaws. One of the most notable of these is double pro-
trusion (Class 11, page 782).
Loss of the deciduous second molar on one side may cause anv of
these irregularities on that side only, such as a semi-constricted or
semi-pointed arch.
Chang-es in Surrounding- Tissues when Teeth are Moved.
1. Resorption axd Deposition.—When a single tooth is moved in
any direction, there is first a compression of the soft and then of the hard
tissues in front of the tooth, and at the same time a stretching of the
