This document discusses four main types of non-elastic impression materials: impression compound, impression plaster, impression waxes, and zinc oxide impression pastes. It provides details on the composition, properties, advantages, and limitations of each material type. Impression compounds are available in high or low fusing varieties and are used to record tooth positions. Impression plaster is similar to dental plaster but has a higher water-powder ratio and mucostatic properties. Impression waxes are used for maxillofacial defect patients. Zinc oxide impression paste is a two-paste system that sets quickly in thin sections and provides good surface detail of ridges.

2.  Four main types of products form the group of
impression materials classified as non-elastic
materials:
 Impression compound
 Impression plaster
 Impression waxes
 Zinc Oxide impression pastes = Cavex

3. Impression Compounds

5. High fusing
 Usually red color cakes/ discs
 Easily breakable – brittle
 Material is softened in temp of up to 85ºC
 It is kneaded to remove folds and then adapted to tray

10. Low fusing
 Ideal for recording peripheries in custom trays
 Material is softened over flame and applied in a
uniform thickness
 It must be tempered in hot water bath before placing
into patients mouth

12.  Used to build up periphery of stock or custom trays
 Material is brought to recordable state by heating over
a flame
 The soft material is adjusted on the tray periphery
then “tempered” in a hot water bath before placing
into patients mouth

14. ZnO paste
 Supplied as 2 pastes system
 White paste – base
 Blue paste – initiator, catalyst
 This material is used for recording edentulous ridges in a
close fitting “custom”/ “special tray” or the patients existing
dentures (if they are not be used further). The material is
mixed in a 1:1 (equal) paste ratio and used in thin sections
only (2-3mm) as a wash impression. Vaseline is used as a
separating agent on those areas requiring protection (soft
tissues, teeth etc). Firm pressure is used during impression
taking.
 Also used to check extension of custom tray periphery
accurate/ over extended/ under-extended)

15.  Composition
 The white paste
 metallic oxides : app. 80 %
 vegetable oil : app. 20 %
The dark blue paste
fatty acid : app. 69 %
fillers : app. 21 %
natural waxes : app. 3 %
organic acid : app. 6 %
pigment : < 1 %

23. BASE PASTE - white
 Zinc oxide
 Inert oils (plasticizer)
 Hydrogenated resins (increases setting time and
improves cohesion)
REACTOR PASTE - blue
 Zinc acetate (accelerator)
 Fillers (talc or kaolin)

24. PROPERTIES
 Non toxic
 Adherence to tissues
 Mucostatic or muco - displacive (depending on brand
used)
 Good surface detail in thin section
 Good dimensional stability (little or no dimensional
change on setting, 0.1% dimensional change during
setting)
 Can be added to.
 Stable on storage and good shelf life

25. ADVANTAGES
 1. Dimensional stability
2. Good surface detail
3. Can be added to
4. Mucostatic or muco-displacive
DISADVANTAGES
 1. Cannot be used in undercuts
2. Only sets quickly in thin section

26. Impression plaster
 Impression plaster is similar in composition to the
dental plaster used to construct models and dies
 It consists of calcined, β-calcium sulphate
hemihydrate which when mixed with water reacts to
form calcium sulphate dihydrate.
 The material is used at a higher water/powder ratio
than is normally used for modeling plasters

27.  Salt can be added as accelerator
 It has mucostatic properties. The setting expansion of
dental plaster is reduced to minimal proportions by
using anti-expansion agents e.g. Potassium sulphate
 Very fine details can be recorded in impression plaster
but its use is limited

28. Limitations
 Cannot be used in undercuts
 Easily fractured

29. Impression waxes
 Used in impression of maxillo-faical defect patients

32.  Periphery wax can be used with all types of impression
materials for making wax stops, post-damming and
lining the periphery of trays. Surgident Periphery wax
is a soft, tacky wax that is easily shaped at room
temperature.