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pared in such models arc diagramatic. and that they are only intended
to illustrate principles. An attempt will be made to give examples of
the various forms of cavity preparation used in filling teeth with por-
celain. Many of these forms may appear to involve the sacrifice of an
unnecessary proportion of tooth structure, but such sacrifice insures
better retentive resistance and a stronger mass of porcelain.

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FIG. 4.

The preparation of cavities for porcelain in-
Tnstrumcnts. lays requires but few special instruments. Figs.
4 and 5 represent the forms of burs and stones that
are particularly indicated in this work. These instruments should be
obtained for both the straight and the angle hand piece.

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Fig. 4, A, represents the regular forms of flat faced fissure burs.
Fig. 4, B, C and D, represent finishing burs, cylindrical, inverted cone
and round in form. These burs are useful in shaping and finishing the
walls and margins of cavities.
Fig. 5, A and B, represent cavity trimmers and diamond burs.
They are useful in cutting away enamel and shaping cavities. The
grit is fine and thev leave the surface smooth.

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