ies (now an accepted practice), and he finds that it prevents
further caries oftener than any other metal or combination of metals he
has ever seen used. In filling such cavities, adjust the rubber, and use
a shield or matrix of such form as to just pass beyond the cervical
margin; this will generally push the rubber out of the cavity, but if it
does not, then form a wedge of wood and force between the metal and the
adjoining tooth, thus bringing the metal against the cervical margin,
and if a small film of rubber should still remain in the cavity, it may
be forced out by using any flat burnisher which will reach it, or it can
be dissolved out with a little chloroform. Fill from one-fourth to
one-half of the cavity with tin, and complete the remainder with gold
when the tooth is of good structure; this gives all the advantages of
gold for an occlusal surface.

Before beginning with the gold, have the tin solid and square across the
cavity, and the rest of the cavity a good retaining form, the same as
for gold filling; then begin with a strip of gold slightly annealed and
mallet it into the tin, but do not place too great reliance upon the
connection of the metals to keep the filling in place.

On the same plan, proximal cavities in the anterior teeth can be filled,
and also buccal cavities in molars, especially where they extend to the
occlusal surface. The cervical margin should be well covered with tin
thoroughly condensed, thus securing perfect adaptation, and a solid base
for the gold with which the filling is to be completed. Time has fully
demonstrated that the cervical margin is most liable to caries, and here
the conservative and preservative qualities of tin make it specially
applicable.

"Electrolysis demonstrates to us that no single metal can be decomposed,
but when gold and tin are used in the above manner they are united at
the line of contact by electrolysis. The surface of both metals is
exposed to the fluids of the mouth, and the oxid of tin is deposited on
the tin, by reason of the current set up by the gold; thus some atoms of
tin are dissolved and firmly attached to the gold, but the tin does not
penetrate the gold to any great extent." (Dr. S. B. Palmer.)

This connection of the metals assists in holding the filling in place,
but it is more likely to break apart than if it was all gold. After
electrolysis has taken place at the junction, it requires a cutting
instrument to completely separate the