Editorial. Memoir of Prof. Chapin A. Harris. [Volume: 2, Issue: 5, December, 1860, pp. 274-288]

286

THE DENTAL COSMOS.

removal, it is unavoidably fractured, the pieces may be retained and replaced with but little trouble.
"Lower impressions may be obtained as readily in plaster as with any
other material, provided a few simple facts are remembered and acted
upon. The plaster should be mixed somewhat thicker than for the superior arch, the same care being requisite in the introduction of the cup and
the position of the head. Directions should also be given to elevate the
tongue while the impression cup is being pressed into place; it should
then be allowed to take its natural position in the mouth; this will prevent
the retention in the impression of any loose folds of mucous membrane or
muscular tissue of the tongue, or its attachments. The same care should
be extended to free the muscles of the cheek.
"The above instructions, if followed, will, in my judgment, give any
operator what is most to be desired in forming artificial dentures, viz.,
a perfect impression of the mouth."
"TAKING IMPRESSIONS. (BY C. M. FORBES, St. Louis, Mo.)-A correct impression of the mouth depends, in a great measure, upon a careful
attention to the details of the operation. It is necessary to be elaborate,
overlooking no part of the operation because it seems to be unimportant.
Every single detail bears a relative importance to the whole, and nothing
can be omitted without affecting the end to be accomplished. It is requisite that the operator should possess a nicety of manipulation; and
quite important that every article should be clean and in order. Having
ascertained the mouth to be in a proper condition for taking the impression, I first select a suitable impression cup, (should prefer silver,) which
must conform, in size and shape, as near as possible to the shape of the
arch. If there be peculiarities in the case, which render the ordinary cup
unsuitable, I would take an impression in wax, get up metallic dies, and
construct a cup out of sheet zinc, which would be perfectly adapted to
the angular form of the arch. Having selected a cup, and arranged convenient for use such articles as will be needed-napkins, wax, plaster,
lamp, etc.,-I heat the wax slowly over a spirit-lamp, working it
thoroughly with the fingers. The wax should be pure, and, if remelted
and worked, it is better than new. When it is sufficiently soft, I take a
first impression of the mouth in wax. After this has become cool, I cut
away the outer alveolar ridge, down to the edge of the cup; a part of the
posterior portion is also cut away. Before taking the second impression,
the patient should be seated in an upright position, with the head a little
forward to prevent the plaster from getting into the throat; and a napkin should be spread upon the breast to prevent the patient's clothes from
being soiled by the plaster or saliva that may drop from the mouth. I
then prepare the plaster, which has been previously dried or boiled, mixing it in warm or tepid water, in which a little salt has been dissolved.
It should be stirred a moment or two until thoroughly mixed. It is then
poured into the wax impression, which is replaced in the mouth, and held
firmly in its place until the plaster sets. This usually requires from three
to seven minutes, depending somewhat upon the quality of the plaster.
When some of the teeth remain in the mouth, and especially when there
is an abnormal absorption of the gums, leaving the necks of the teeth
bare, the removal of a plaster impression from the mouth without injury
to it, is often attended with considerable difficulty; but by exercising care
and patience, the operator will seldom fail to obtain a good impression;