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REVIEW OF DENTAL IMPRESSION
MATERIALS
R.G. CRAIG
Department of Biomaterials, School of Dentistry, University of Michigan, Ann Arbor, Michigan 48109
Adv Dent Res 2(l):51-64, August, 1988

ABSTRACT
Major advances in impression materials and their application have occurred during the last decade, with greater emphasis being placed on rubber impression materials than on dental compound, zincoxide-eugenol, and agar and alginate. Of particular interest has been the effect of disinfection solutions on the qualities of impressions and the biocompatibility of impression materials. The principal advance in hydrocolloids has been the introduction of the agar/alginate impression technique, which has simplified the procedure and
improved the quality of gypsum dies compared with those preparedin alginate impressions. The tear strength of some alginates has been improved, and some have been formulated so that the powder is dustless, thus reducing the health hazard as a result of patient inhalation of dust during the dispensing process. Polyether
and silicone impression materials have been modified so that the working time, viscosity, and flexibility of the
polyethers have beenimproved and, with the introduction of addition silicones, their accuracy has become
exceptional. Although the early addition silicones liberated hydrogen after setting, thus delaying the pouring
of models and dies, most addition silicones have been improved so that no hydrogen is released and dies can
be poured immediately. The introduction of automatic mixing systems for addition silicones hassimplified their
manipulation, has reduced the number of voids in impressions, and has reduced the amount of material wasted.
The incorporation of surfactants into addition silicones has made them hydrophilic, with wetting properties
similar to those of polyethers, and has made pouring bubble-free gypsum dies easier.
This review is confined to published and unpublished information of the pastdecade. It will also suggest
trends that should be anticipated in the near future based on this information. The review will not present
information developed before 1975, which is available in several textbooks on dental materials by Craig (1985a),
Phillips (1982), and Williams and Cunningham (1979).
RIGID IMPRESSION MATERIALS
IMPRESSION COMPOUND
The use of dental tray compound has decreasedwith the increased substitution of acrylic tray materials.
The application of dental impression compound
has also decreased with the increased use of rubber
impression materials, which can also be electroformed
to produce metal dies. However, impression
compound is useful for checking cavity preparations
for undercuts and for making impressions of full crown
preparations where gingivaltissues must be displaced.
Excessive temperature rise of the pulp chamber
is undesirable, and Grajower et al. (1975) recently
measured temperature increases in the pulp when
Presented at the International State-of-the-Art Conference on Restorative
Dental Materials, September 8-10, 1986, National Institute
of Dental Research
compound impressions of crown preparations were
taken in copper bands.They measured temperatures
of up to 53°C when the bands were heated in an
uncontrolled manner, <44°C when bands were flamed
under controlled conditions for about one min, and
to about 41°C when the bands were heated for seven
min in 52°C water. No graininess was observed at a
magnification of 10 x for this last condition. Temperature
measurements showed that when the impression
cools onits own, the pulp temperature is >37.5°C
for more than three min. Chilling should start as soon
after seating as possible, and chilling times of approximately
20 and 30 sec were recommended for
copper band impressions of incisors and molars.
ZINC OXIDE-EUGENOL
Although zinc oxide-eugenols are excellent materials
for wash impressions of edentulous areas, they
have been replaced to a...