Page 47 - My FlipBook

NOMENCLATUBE. 15

long axis of the tooth and may be supposed to cut through the
crown at any point in its length.
The axio-mesio-distal plane, or the mesio-distal plane,
Figure 10, passes through the tooth mesio-distally parallel with
its long axis.
The axio-bucco-lingual plane, or the biicco-lingual plane,
Figure 11, passes through the tooth bucco-lingually parallel
with its long axis. In the incisors and cuspids this is the labio-
lingual plane.
The inclination at which walls of cavities are cut, or of
the dentin wall and the enamel wall, when each is specifically
mentioned, is reckoned from these planes of the teeth. When
great accuracy of statement is desired, the inclination may be
given in centigrades. Moi-e generally the term, outward inclina-
tion, or inclined outward, is used, with some word expressing
degree, as slightly, strongly, etc. In this use of words the wall
of the cavity mentioned is always inclined away from the plane
of the tooth in passing from within outward. The enamel wall
and the dentin wall of any given part of a cavity may be on dif-
ferent inclinations; for instance, the lingual dentin wall of a
mesial cavity in a first molar tooth may be cut in the mesio-distal
plane and the enamel wall inclined outward five or six centi-
grades, as shown in Figure 8. This will make a slight angle at
the dento-enamel junction.
The bevel of the cavo-surface angle is always reckoned from
the plane of the enamel wall.
The Use of Divisions op the Sukfaces of the Teeth in
Cavity Description.
Whenever we wish to indicate in words the portion of a
surface of a tooth involved in decay, or the extent of a cavity,
we may conveniently do so by an imaginary division of the
surface into thirds, fourths or fiifths. This division may be
mesio-distally upon a buccal, lingual, or occlusal surface, or
occluso-gingivally upon a buccal, lingual, mesial or distal sur-
face, or it may be bucco-lingually upon an occlusal, mesial or
distal surface. In other words, the divisions may be made upon
any one of the planes of the tooth. Figures 12, 13, 14.
For instance, of a cavity in a buccal surface, we may say
it involves the middle third mesio-distally of the gingival third
occluso-gingivally. Or, if the cavity is broader, we may say it
involves the middle three-fifths bucco-lingually of the second
fourth of the surface occluso-gingivally, as in Figure 14.