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CHAPTER XV.
MANAGEMENT OF PROXIMAL CAVITIES IN INCISORS IN-
VOLVING THE ANGLE. (CLASS FOUR.)

Definition. Cavities of Class Four are those in which the incisal
angle has either been lost or can not be safely retained. The deci-
sion as to its restoration is of most vital importance. To cut the
angle from nearly every incisor which has a proximal decay is little
short of malpractice, while at the same time to attempt to save those
not wholly and adequately supported by dentine is to invite many
disastrous failures.
Conditions Demanding Frequent Angle Restoration. First. When
contact is in the incisal third. In such eases a verj^ small decay will
involve all of the dentine toward the incisal angle.
Second. Incisors which have long flat proximal surfaces. Such
teeth will show a line of decay extending gingivo-incisally and may
entirely weaken the incisal angle before the pulp is in danger.
Third. The pulp may be involved and its removal materially
lessens the resistance of supporting dentine at the angle.
Fourth. The angle under consideration may be so located that it
is frequently requii'ed to stand great stress in service. This is a
point Avhich must not be overlooked as an angle Avhich stands well
exposed must bear much greater and more often repeated force than
an angle which does not occlude or can not be brought into articula-
tion.
Difference Betw^een Mesial and Distal Surfaces. The above four
conditions will be more frequently met with in mesial surfaces,
hence the mesial angles are in greater danger and more often re-
quire restoration.
Plans of Angle Restoration. There are four general plans of re-
storing the incisal angle Avhich are worthy of consideration. Many
plans have been advanced from time to time, but the four given
below seem to have remained in favor.
Retention Form in Class Four Fillings. With each of the plans
presented and generally practiced the effort is made to remove or
nullify the principle of the lever.
With proximal fillings wherein the force of mastication is brought
in direct contact with the filling the principles of the lever must be
reckoned with. The force of mastication is the power, the filling the
lever, the anchorage in the point angles the load and the point on
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