Page 184 - My FlipBook

152 FILLING MATERIALS

Disadvantages.
1. Lack of edge strength.
2. Low crushing resistance.
3. SolubiUty in the fluids of the mouth.

4. Incapabihty of polish (except siUcates).
5. Change of molecular form while setting (some ex-
pand, some shrink).
Method of Mixing Cements.—Use a dean glass slab (Fig.
178), with a heavy, steel, ivory, bone or agate spatula (see
For the silicates, no steel instruments can be used
Fig. 95).
in the mixing or packing, on account

of chemical action, and consequent
discoloration of the mass. Tanta-
lum, agate, ivory, stellite, or tortoise-
shell instruments are recommended.

The oxychlorid of zinc and oxyphos-
phate of copper are mixed to a creamy
consistence; the oxyphosphate of zinc
^o the Consistence of putty for fining,
Fig. i78.-Giass cement slab,
and to a creamy consistence for set-
ting crowns, inlays and regulating appliances. The silicates
are mixed stiffer than the oxyphosphate of zinc, working

in all the powder possible, which will be greater in amount
than that taken by the liquid of the zinc phosphate cements.
Directions.— (i) Place, by means of a glass rod or pipette,

the necessary amount of liquid in the center of the clean slab.
(2) Deposit, by tapping the bottle, or with a clean spatula or
other convenient carrier, the necessary amount of powder at
one end of the slab. (3) Draw in one-fourth of the powder
and spatulate thoroughly with a swinging, circular movement.
(4) Then draw in another one-fourth of the powder and spatu-

late as before until thoroughly mixed, continuing to add the
powder, and spatulating until the mix is of the desired con-