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PROXIMAL CAVITIES IN INCISORS AND CUSPIDS 75

larly in the larger cavities, as eases Avill be met in Avhich it will
be found necessary to remove the incisal angle to secure proper
** retention form." This looking to the incisal first Avill decide
this point early in the procedure.
The Incisal Line Angle should meet the axial wall at least at
a right angle. In cases where this line angle is short, as^found in
shallow cavities, the incisal line angle should meet the axial wall
at a slightly acute angle. It is not necessary to make a convenience
atigle at the incisal point angle. (Fig. 34.)
The bevel angle on the gingival wall becomes the fulcrum. It
is only necessary that the distance from this point to the incisal
point angle be greater than that from the same point on the gin-

Fig. 34.—Drawing to illustrate the retention at the incisal angle of Class Three cavity.
In shallow cavities with a short incisal line angle as d— b, the angle at b should be acute.
In deeper cavities and longer incisal line angles as the one shown at d— c, the incisal point
angle is efficient if it is a right angle and may even be obtuse. In the illustration shown
the filling would pivot to exit at a. Dotted lines a— fc and a— c are the same length hence
the point angles of the two fillings would describe an arc of the same circle in tipping to exit.
gival wall to the most external portion of the incisal line angle.
The more shallow the cavity in Class Three the more acute must
be the incisal point angle.
Other Point Angles. The gingivo-axio-labial and the gingivo-
axio-lingual point angles are now carried into the dentine at the
expense of both axial and external Avails, care being given not to
groove the gingival Avail.
Line Angles. Line angles are made Avith small hatchets and hoes
of suitable sizes, say, one-third to one-half millimeter in Avidth, Avith
edges that are keen and Avhose corners are Avell defined, not having
been rounded through careless sharpening or Avear.