Page 642 - My FlipBook

312 THE TECHNICAL PEOCEDXJEES IN FILLING TEETH.

MODIFICATION OF SILVER-TIN ALLOYS BY THE ADDITION OF
OTHER METALS.
The appended table shows a fairly full range of these that
may be studied. Careful experiment has shown clearly that
additions of more than five per cent of any of these metals will
show positive injury in some direction, and a number of the
metals in any proportion will cause injury. It will be noted
in studying the exhibit that cadmium and aluminum are inju-
rious in any quantity. Experiment in watching fillings for five
years shows also that one-half of one per cent of zinc is
inadmissible for the reason that the amalgam will continue to
change bulk very slowly for that time and perhaps much longer.
Though this change is not large (not more than one to one and
one-half points per year with one per cent of zinc), it will finally
destroy the usefulness of the filling. This effect is so subtle
that it was not at first discovered.
No advantage whatever is derived from adding gold or
platinum to alloys, but so long as these are used very sparingly,
they do not do much harm.
Copper, not more than five per cent, if alloyed with the
silver before combining with the tin, so as to insure a perfect
alloy, increases the strength of the amalgam without doing
injury in other ways and seems desirable. In my present view,
it is the only modifying metal thus far known that is desirable.
EXHIBIT OF MODIFIED SILVER-TIN ALLOYS.
Formulv.
Silver.
Modifying Metal.
None
None
None
None
Gold 5
Gold 5
Platinum 5 .
Platinum 5 .
Copper 5 . . .
Copper 5 . .
.
Zinc 5
Zinc 5
Bismuth 5 .
Hismuth 5 , ,
Cadmium 5.
Cadmium 5.
Lead 5
Lead 5
Aluminum 5.
Aluminum 1.
Aluminum 1.