c. Recommended Procedures. Any of the gypsum products can be poured
against a modeling plastic impression without the use of a separator. Also, modeling
plastic is one of the impression materials against which an amalgam die can be packed.
(An amalgam die is a model of a tooth in silver amalgam, used for making an inlay or
crown.) Although no separating medium is required in either of these procedures,
extreme care must be exercised in drawing the impression material from the cast or die
since both materials are hard and relatively unyielding. Therefore, the modeling plastic
is softened in water heated to 120 F (49 C) and removed gently so that the cast is not
3-23. IMPRESSION PASTE--CHARACTERISTICS
a. General. Impression paste is a thermoplastic-type impression material. It is
usually supplied as two separate units--a base and a hardener. The principal
ingredients are zinc oxide and eugenol. When the base and the hardener are mixed
together in specific proportions, they form a paste. No separator is required when
pouring the cast in an impression taken with this material.
b. Usage. Impression paste is used primarily as a corrective material inside an
individual impression tray. It is also widely used for rebase impressions for both
complete and partial dentures. (A rebase impression replaces the base material of a
denture without changing the occlusal relations of the teeth.) Occasionally, it is used in
immediate denture fabrication as a lining for a sectional compound impression.
Impression paste can be used to provide a lining for a complete denture baseplate to
make it fit both the cast and the mouth accurately.