Page 194 - My FlipBook

178 THE TREATMENT OF TEETH
reasonable time if left alone. In order to save
time it has been suggested that the asbestos
should be mixed with alcohol, and then the alcohol
set fire to and blazed off. This, however, produces
a much more friable and more easily damaged
investment than if water were used, and as an
investment of asbestos and water can be com-
pletely dried in five minutes if necessary, there is
only a saving of about three or four minutes in
using alcohol, and if the alcohol investment is
accidentally dropped on the floor it flies all to pieces.
It also happens that unless great care is taken some
of the more friable alcohol and asbestos investment
may be rubbed off and become mixed up with the
inlay body. The writer is indebted to Mr. T. M.
Mitchell for the method of rapidly drying the
investment, which is as foUows:—Place the tray
containing the invested matrix on a stand over
a spirit-lamp. (The lid of a small tin box on two
improvised uprights will serve the purpose.) The
flame at first must be very small. Prick into the
investment every now and then with a probe or an old
excavator, so as to allow the steam to escape, and as
soon as the investment becomes sufficiently dry to
admit of it, scrape two small holes in it, one at each
end of the tray between the matrix and the edge of
the tray. At first the holes will fill up as soon as