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150 FILLING MATERIALS

2. In cavities of easy access, heat the Gutta-percha and,

while soft, mold into a mass of sufficient size to fill the cavity,
packing with a warm burnisher, condensing thoroughly against
the walls, and trimming the excess after either of the above
methods. Then go over the surface of the filling with a
pledget of cotton or spunk, moistened with chloroform. For

illustrations of burnishers see Figs. 93 and 94.
Technical Exercises.
Fill several of the cavities, prepared during the study of
cavity preparation, using both methods as outlined above.

CEMENT

There are four varieties of cements used in dentistry, each
receiving a name depending on its chemical composition.
Cements consist of a powder and a liquid, which when mixed
together, form a more or less hard mass. The composition of

these is largely a trade secret, but for all practical purposes it
is as follows

Classification of Cements '
1. Oxyphosphate of Zinc ( Powder, Zinc Oxid (calcined)
(Basic Zinc Phosphates) I Liquid, Phosphoric Acid
^ . , , „ f Powder, Cupric Oxid
^
2. Oxyphosphate of Copper < _ ., „,
"^ ^ ^^ [ Liquid, Phosphoric Acid ,
,
.
.
.
.
_,,.,.„. f Powder, Zinc Oxid (calcined)
3. Oxychlond of Zinc < _ . . , „, „, , . , ,, ,. ..
[ Liquid, Zinc Chlorid (deliquesced)
Beryllium,
Powder ^f"^'.
4. Silicates. Aluminum,
Calcium Compounds
Liquid, Phosphoric Acid
Characteristics.—All of the cements are intended for. tem-
porary filling work, unless covered by some more permanent
material, as they are more or less soluble in the oral fluids, (i)
The Oxyphosphate of Zinc (basic zinc phosphates) is the most