a lower conductivity than
gold. A new filling is harder than tin, softer than gold, but after a
time it becomes as hard as amalgam. It oxidizes and thus helps make
tight margins, and is very useful at cervical margins; generally
discolors, but not always, and does not discolor the tooth unless a
carious portion has been left, and then only discolors that portion. In
oral fluids it is indestructible if well condensed, otherwise it is
crumbly. There is no change of form, except a _slight_ expansion, which
does no harm. A weak electric current is set up between the gold and
tin, and tin oxid is formed. The hardening and discoloration both depend
upon the separation of the tin by the electrical action and its
deposition on the surface of the gold. I generally prepare cavities the
same as for non-cohesive gold, but a Tg filling may be held in a more
shallow cavity and with less undercuts than for gold. Hand pressure is
adopted, but a mallet may be used advantageously. Lay a sheet of No. 4
non-cohesive gold on a sheet of No. 4 tin, then cut into strips and
twist into ropes; keep the tin on the outside, for it does not tear as
easily as gold. Carry the material against the walls and not against the
base, otherwise the filling will be flat or concave; but should this
occur, then force a wedge-shaped plugger into the center of the filling,
and drive the material toward the walls, and then fill the hole or
remove all the filling and begin anew.

"In very deep cavities use a mat of Tg, dampened in carbolic acid and
dipped in powdered thymol, as a base; this has an antiseptic action, and
also prevents pressure on or penetration into the pulp.

"Drs. Abbot, Berlin; Jenkins, Dresden; Sachs, Breslau, have observed
tin-gold fillings from fifteen to twenty-five years, and say that for
certain cases it is better than any other material. I use square-pointed
pluggers (four-cornered), as part of the packing is done with the side
of the plugger. Tg is useful in partly erupted molars, buccal cavities
under the gums, occlusal cavities in temporary teeth, cavities where all
decay cannot be removed. Use Tg with a gold capping in small, deep
occlusal cavities, cavities with overhanging walls, occlusal cavities
with numerous fissures, large, deep occlusal cavities near the pulp, in
proximal cavities.

"Line labial walls of incisors with non-cohesive gold, and fill the
remainder with Tg. For repairing gold fillings I use Tg." (Dr. Miller,
Berli