Page 23 - My FlipBook

METHODS OF TAKING IMPRESSIONS. II
—
Tests for Perfect Impression. 'Jhc most reliable test for
a perfect impression is the degree of resistance to its removal.
The time for removal can he ascertained by breaking a
small piece of the plaster from the surplus in front ; as soon
as there is a clean, sharp break the impression should be
promptly removed. If left in beyond this time the mois-
ture may be extracted from the mucous membrane causing
greater adhesion and possibly rupturing that delicate
surface.
Manner of Removing Impression.-—The resistance which
results from the exclusion of the air from between the
plaster and the mucous membrane of the palate should be
considered where a perfect impression has been secured.
This is best overcome by raising the lip and cheek on the
sides and in front, allowing the air to pass in over the rim
of the tray; which will usually allow it to be readily re-
moved. Should there be further difficulty, however, the
air may be admitted by pressing up the soft palate at the
rear of the tray; or the patient may be directed to give a
slight cough; this will raise the soft palate and admit the
air between it and the impression, allowing it to be easily
taken out.
Full Lower Impression.—A tray of suitable shape (see
Fig. 4) and size should be selected, and modified with
a rim of wax to suit the case in hand ; it is also advisable,
especially where a new or very smooth tray is to be used, and
where the mouth presents a decided undercut, to place a film
of wax over its surface to prevent the plaster leaving it.
Fill the tray with plaster, prepared as before, then step
to the right side and a little in front of the chair, facing
the patient, so that you may more readily see to place the
best; give 10 grains before retiring, 20 grains the following morning,
and 20 grains additional in a few hours ; one hour after which take
impression. Local treatment consists in making application of cocain
or manipulating the parts with a feather or edge of a napkin, or in
gargling the throat with camphor water just before taking impression.