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194 CLASSIFICATION OF DECAYED CAVITIES.

It is often the case, that the finger is too short to
reach a desired point, to hold down a napkin, or
paper, or hold away the soft parts, or so large as to
fill the space inconveniently, obstructing the view or
the operation. To overcome both of these difficulties
an extension thimble is used; it may be made of silver
or rubber, though better of the former. In addition

to the uses mentioned it may by having a fine steel
point, be used to aid in introducing fillings. (Fig. 51.)
Fia 51.

Various appliances have been used for holding

away the cheek, keeping down the tongue, and re-
Fie. 52.

taining the jaws apart. A good instrument, however,
for this purpose is shown in Fig. 52.