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12 MECHANICAL DENTISTRY AND METALLURGY.

tray in the proper position. Distend one corner of the
month and the cheek with the side of the impression tray
as it is being- passed into the month, and the other at the
same time with the left hand, and adjnst the cup to the
ridge, that is, place it so that the center of the cup will come
directly over the top of the ridge.
Fig. 4.

Now step back quickly to the position taken for upper
impressions, pass the left hand back of and around the
patient's head ; press the cheeks away from the impression
tray when necessary, so there will not he a fold of membrane
underneath; then with the thumbs, one on either side over
the center of the ridge, press the cup down carefully but