Page 192 - My FlipBook

l6o FILLING MATERIALS

1. Binary—one containing mercury and one other metal.
Example, copper amalgam.

2. Ternary—one containing mercury and two other
metals. Example, Townsend's amalgam, containing mer-
cury, silver and tin.
3. Quaternary—one containing mercury and three other

metals (Black's amalgams). Example, mercury, silver, tin
and copper.
4. Quinary—one containing mercury and four other
metals. Example, mercury, silver, tin, copper and zinc.
Most of the amalgams in use today are either Quaternary or
Quinary amalgams.

Classification of Alloys

Alloys may be classified into two divisions, as follows:
1. High-percentage, or Quick-setting Alloys (containing
a high percentage of silver).

Formula: Silver 65 to 68 per cent
Tin 26 to 28 per cent
Copper 3 to 4 . 5 per cent
Zinc I to 2 . 5 per cent
Properties.— (i) Quick setting. (2) Hard working (lack

of plasticity). (3) Great crushing resistance and edge
strength. (4) Stability of form (minimum of shrinkage,
expansion and flow). These alloys are sometimes designated
Dr. Black's alloys, but they are wrongly named, as they do
not follow his formulae.

2. Low-percentage, Slow-setting or Plastic Alloys.
Formula: Silver 43 to 48 per cent
Tin 48 to 58 per cent
Zinc I to 2 p'er cent
Properties.— (i) Slow setting. (2) Lighter in color. (3)
Plasticity (easy working). (4) Less crushing resistance and