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1 68 FILLING MATERIALS

lengths are required, depending on the size and depth of the
cavity. Gold cylinders in both cohesive and non-cohesive
forms are also prepared ready for use by the manufacturer I

(Fig. 183).
5. The Cushion or Mat.—Fold a ribbon lengthwise upon
itself with a spatula, until made into a mat or cushion. The
size will depend on the size of the cavity, and may be varied
by regulating the width of the ribbon, the amount of gold

used and the number of folds.
Another Method.—Roll a cylinder on a flat-sided broach,
and then, after withdrawal from the broach, flatten it more;
or roll the cylinder as usual and flatten into a mat.
Advantages of Tin.
1. Non-conductivity. (Lowest of all the metals.)

2. Ease of introduction. (Works rapidly when non-
cohesive.)
3. Adaptability to cavity walls.
4. Therapeutic action. (Supposed by some to prevent

decay.)
5. Capability of polish. (It takes a high polish, but does
not retain it.)
Disadvantages.
1. Inharmonious color. (Oxidizes and darkens readily.)
2. Lack of crushing resistance and edge strength.

3. Flow.
4. Disintegrates in the fluids of the mouth.
Tin is still used by some operators for filling cavities in
children's teeth on account of its ease of introduction and
supposed therapeutic effect; also in rapid caries on surfaces

unexposed to view and mastication. It is too soft to be
subjected to the forces of occlusion in permanent teeth. As
the method of working non-cohesive gold and tin is identical,
the description here given will apply to both materials.