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192 THE TECHNICAl, PBOCEDURES IN FILLING TEETH.

In distal surfaces nearly the same conditions will occur but
will be found less frequently. In these the angle is more rounded
in form and the contact point is farther from the incisal edge.
For this reason the incisal angle is less frequently involved;
indeed, is but rarely involved in cavities that are yet small.
Otherwise than these points the conditions in distal surfaces
will be similar to mesial surfaces and require similar treatment.
This applies to the mesial and distal surfaces of the lateral incis-
ors in all respects, except that these are smaller teeth, which
increases the difficulty of treatment in eases in which an incisal
angle must be restored.
The plans of repair in these several conditions will differ
with the amount of substance lost, and the opportunities offered
for anchorage in the remaining parts of the tooth. In each of
these the position of the pulp in relation to the incisal edge,
whether it is near to or far from it, becomes important. The
pulp extends farther toward the incisal edge, and is larger in
young people than in older persons. In teeth with very thin
incisal edges, the pulp extends proportionally nearer the incisal
edge than in thick teeth, and especially it extends nearer the
incisal edge of the dentin, leaving less room for anchorage in
the dentin between the pulp and the incisal enamel. The longer
and thinner labio-lingually the crown, the shorter proportionally
the distance from the incisal edge of the pulp to the incisal edge
of the dentin. The two central incisors may often be shortened
by grinding the incisal edge in imitation of normal wear with-
out material injury to their appearance. By such grinding,
the remaining edge is left thicker so that a thicker and stronger
angle of filing material may be built. All of these points must be
considered in planning for the building of broken angles. Quite
a large majority of these occur on mesial angles, seemingly
because the contact point is usually nearer the incisal edge on
mesial surfaces, and therefore decay begins nearer the incisal
edge.
General statement of choice of plans. (1.) Wlien there
is room for anchorage in the dentin between the pulp and the
incisal edge without danger to the pulp, the plan of undercutting
the incisal edge may be chosen. This has the merit of disfigur-
ing the tooth less than the incisal step plan (compare Figures
275 and 278) and, in case the pulp is exposed, the cutting is in
line for its removal and the use of the pulj) chamlier for anchor-
age. (2.) When there is not room to make sufficient anchorage
by undercutting the incisal edge, an incisal step should be made