Page 318 - My FlipBook

316 PLASTIC FILLING MATERIALS.
amalgams, each having its own time of setting and rate of contraction.
If only enough mercury has been used to make a creaky mass the sur-
faces of eacli alloy particle are covered by an amalgam of indefinite
composition which acts as a cement binding the particles together. In
this line the same experimenter has shown that mixing the alloy and
mercury in a mortar by means of a pestle, wringing the surplus mer-
curial solvent from the mass by means of heavy pliers, and packing the
filling with steel burnishers are all influences which lessen the strength
of the completed filling.
The conditions are now a prepared and sterilized cavity ; any miss-
ing wall required to give four sides has been replaced by a properly
adjusted matrix (see Figs. 255, 256, Chapter XII.).

Fig. 275.

Dr. Herbst's matrix.
Matrices.—Matrices may be readily and quickly formed by cut-
ting strips from a sheet of very thin steel which has been annealed

Fig. 276.

Fig. 277.

Herbsl pliers.

and polished. By means of contouring pliers the matrix is given
the correct contour, then wedged or tied into place. They must