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CHAPTER yill.

PREPARATION OF CAVITIES—OPENING THE CAVITY—RE-
MOVING THE DECAY—SHAPING THE CAVITY—CLASSI-
FICATION OF CAVITIES.
By S. H. Guilford, A. M., D. D. S., Ph. D.

General Considerations.—The importance of the proper preparation
of a cavity for the insertion of a filling can scarcely be oyerestimated.
Upon its being well done the success of the completed operation largely
depends. As many fillings fail from lack of thoroughness in the pre-
paration of the cavity as from any other cause.
The operator should not be actuated by haste, but should be deliber-
ate, careful, and painstaking. Each stage of the operation should be
thoroughly performed in order that when completed the cavity may be
in the best possible condition for the reception and retention of the
filling.
The operation is naturally divided into three stages :
1. Opening the Cavity.
2. Removing the Decay.
3. Shaping the Cavity.

Opening the Cavity.
Every cavity to be excavated must first be opened, so that it may be
approached and operated upon at all points. The particular manner of
doing this will have to be determined by the extent of the decay and its
position, but in all cases the opening must be as full and free as the
conditions will permit.
The accessibility of the cavity will depend upon its location. Upon
the three exposed surfaces of a tooth crown (occlusal, lingual, and labial
or buccal) access to a cavity is usually easy, but upon the unexposed
surfaces (a])proximal) access can only be had after the teeth have been
pressed apart. For methods of securing temporary separation of the
teeth see Chapter VI.
A cavity U])on an exposed surface, if small, can usually best be
opened by the use of some form of engine buk. A few sizes each of
the forms known as " fissure," " inverted-cone," and " round " (or
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