element; thus when
they form the voltaic pair, the tin becomes coated or oxidized and the
current practically ceases.

There is more or less therapeutical and chemical action in cavities
filled with tin, and its compatibility and prophylactic behavior as a
filling-material depends partly upon the chemical action which occurs.

Some dentists fill sensitive cavities with tin, in order to secure
gentle galvanic action, which they believe to be therapeutic,
solidifying the tooth-structure.

"Tin possesses antiseptic properties which do not pertain to gold for
arresting decay in frail teeth; it not only arrests caries mechanically,
but in chalky (imperfect) structure acts as an antacid element in
arresting the galvanic current set up between the tooth-structure and
filling-material." (Dr. S. B. Palmer.) If the metal is acted on, the
tooth is comparatively safe; if the reverse, it is more or less
destroyed. The galvanic taste can be produced by placing a piece of
silver on the tongue and a steel pen or piece of zinc under it; then
bring the edges of the two pieces together for a short time, rinse the
saliva around in the mouth, and the peculiar flavor will be detected.

"In 1820 attention was called to the injurious effects of the galvanic
current on the teeth, and dentists were advised never to use tin and
amalgam in the same mouth.

"A constant galvanic action is kept up in the mouth when more than one
kind of metal is used in filling teeth, and galvanism is often the
cause of extensive injury to the teeth. The most remarkable case I ever
saw was that of a lady for whom I filled several teeth with tin. After a
time decay took place around some of the fillings. I removed them and
began to refill, but there was so much pain I could not proceed. I found
that by holding a steel plugger an inch from the tooth I could give her
a violent galvanic shock. I observed that the exhalation of the breath
increased the evolution of galvanism." (Dr. L. Mackall, _American
Journal of Dental Science_, 1839.)

"When a faulty tooth in the upper jaw had been stopped from its side
with tin, the interstice between it and the adjoining tooth being quite
inconsiderable, while the upper surface of a tooth not immediately
beneath it in the lower jaw was stopped with the same metal, I have
known a galvanic shock regularly communicated from one tooth to the
other when by the movement of jaws or cheeks they were brought near
together." (Dr. E. Pa