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FILLING BY CLASSES AND MODIFICATIONS. 207

to manipulate with facility, and to see as directly as
possible into the cavity.
Cavities of this class are various in form; and they
require much skill in their excavation and formation.
Great care is to be exercised not to leave any portion

of decay in them. By a fatal oversight, decayed den-
tine is often permitted to remain on that side next to
the neck of the tooth; and we have seen fillings that
in other respects were good, very deficient here; so
deficient, indeed, that a sharp instrument would
readily penetrate the softened dentine above them,
or even pass between the filling and the wall of the
cavity. The removal of the decay from the cervical

walls of all proximal cavities is an important particu-
lar, neglect of which occasions thousands of failures.
This class of cavities at this point should be most
thoroughly filled; for it is a point more vulnerable
than any other, on account of the facility with which
foreign substances are here lodged and retained.
In the formation of these cavities the cervical wall
should be made to incline slightly inward, and the

lateral walls, if the tooth will bear the loss, made at
least parallel with each other;' but if that would im-
pair its strength, grooves or pits may be made upon
them for this purpose at proper points. When these
cavities are large, the dentine is usually all decayed
in that part of the cavity next to the masticating sur-