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CAVITY PREPARATION. 105

CAVITY PREPARATION.

DEFINITION. By the phrases "Excavation of cavities,"
"Preparation of cavities," or "Cavity preparation," is
meant such a mechanical treatment of the injuries to the teeth
produced by dental caries as will best fit the remaining part of
the tooth to receive a filling restoring the original form, give it
strength, and prevent recurrence of decay in the same surface.
To do this best requires a good knowledge of the pathology of
dental caines, as a basis for further study by observation and
practice. In this place certain leading facts as to the character
of these injuries, and the steps of the pi'ogress of caries, though
given before, will be regrouped and given as a guide to the begin-
ning of the work of cavity preparation.
Brief Review op the Injuries to the Teeth by Caries, in Their
Relation to Cavity Preparation.
ILLUSTRATIONS: FIGURES 111119.
Caries never begins on clean, smooth surfaces of the teeth.
So long as the function of mastication of food is normally per-
formed, much the greater proportion of the surface of each tooth
is habitually kept sufficiently clean to prevent caries from begin-
ning. In chewing, food stuff is forced over the surfaces of the
teeth at each meal time, cleaning most of the surface of each
tooth, preventing decay at all points so cleaned. There are, how-
ever, certain regions of the surface of each tooth that are so pro-
tected by their i^osition, or by their form, that they are not well
cleaned by this process. Of these there are two main divisions
in which caries occurs : (1) Pit and fissure cavities ; (2) Smooth-
surface cavities.
Pit and fissure cavities. These occur in the pits, fissures,
or deep grooves in the occlusal surfaces of the bicuspids and
molars, less frequently in pits in the occlusal half of the buccal
surfaces of the molars, and occasionally in pits in the lingual
surfaces of incisors. In a few instances also caries will occur
in the lingual portion of the disto-lingual groove of the upper
molars, or in the mesio-lingual groove when there is a fifth cusp
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