1. Elastomeric Impression Materials
Part 1
Dr. Noland Naidoo

2. Classification Impression Materials Non-elastic Plaster Compound
Impression wax
ZnO- Eugenol
Elastic
Aqueous Hydrocolloids
Agar (Reversible)
Alginate (Irreversible)
Non-aqueous Elastomer
Polysulfide
Silicones
Condensation
Addition
Polyether

3. Introduction Rubberlike elastic impression materials
Currently referred to as elastomers or elastomeric impression materials.
Elastomeric material consists of large molecules or polymers that are joined by a small amount of cross- linking
Cross linking form a three-dimensional network
The amount of cross-linking determines the stiffness and elastic behaviour of the material

4. Requirements
Accuracy- must reproduce the entire surface upon which the prosthesis to be made will fit
Elasticity- low elastic modulus and high elastic range
Dimensional stability- the way in which accuracy varies with time after recording the impression
Ease of handling
Good tear strength
Non-toxic and non-irritating
Compatible with die and model materials

5. Classification Impression Materials Non-elastic Plaster Compound
Impression wax
ZnO- Eugenol
Elastic
Aqueous Hydrocolloids
Agar (Reversible)
Alginate (Irreversible)
Non-aqueous Elastomer
Polysulfide
Silicones
Condensation
Addition
Polyether

6. Classification
The ADA considers three types of elastomeric material and each type can be further divided into four viscosity classes:
light body
medium body
heavy body
putty

7. Polysulphides
Supplied in the form of two pastes- a base and a catalyst
Examples: Permlastic (SDS/Kerr), Coe-Flex, Omniflex (GC America)
The base paste consists of:
Polysulphide polymer
Suitable filler (titanium dioxide or lithopone)
Plasticizer ( eg. dibutyl phthalate)
Sulphur – small amount that enhances reaction ( catalyst)

8. Polysulphides The catalyst paste: Lead dioxide
Plasticizer- chlorinated parafin
Approx same amount of filler as in base paste
Oleic or stearic acid- retarders- control the rate of setting

9. Polysulphides Must be used with a special tray
Reasonable tear strength and good elastic properties
Unpleasant odor and taste
Work well in the presence of moisture- moderately hydrophilic
Used commonly for crown and bridge impressions
Casts should be poured within 24hrs of impression but not immediately as to allow for full elastic recoil
Reported incidences of allergic reaction to patients sensitive to latex
Impressions made from polysulfide materials should be poured within 30 minutes following removal from the mouth, because in the first hour they undergo 50% of their 24-hour shrinkage.

10. Poor dimension stability
Polysulphides
Advantages
Disadvantages
Good tear strength
Poor dimension stability
Good elasticity
Offensive odor
Low cost
Stains clothing
Long setting time

11. Polysulphides

12. Silicones Condensation silicone impression material
Supplied in a base paste and low viscosity liquid
Examples: Speedex (Coltene/Whaledent), Accoe (GC America)
McCabe and Walls, 2008

13. Silicones Condensation silicone impression material
Setting characteristics more favourable than polysulphide
Setting time shorter and elasticity developed earlier
Very hydrophobic- repelled by water or saliva therefore necessary to dry areas of the mouth for an acurate impression
Adequate tear resistance for most purposes
Models must be poured as soon as possible after impression recordings
The increased use of addition silicones has lead to a gradual decline in the use of addition silicone

14. Silicones Condensation silicone impression material
Advantages
Disadvantages
Moderate tear strength
Poor dimensional stability
Good working time
Poor wetability
Good setting time

15. Silicones Addition silicone impression material
Also supplied as two paste
The hydroxyl group from the condensation silicone is replaced by vinyl group
Examples: Extrude, Take 1 (SDS/Kerr), President (Coltene/Whaledent), Express, Imprint II (3M ESPE), Examix, Exaflex (GC America), Reprosil, Aquasil, Hydrosil (Dentsply/Caulk)

16. Silicones Addition silicone impression material
Properties are similar to condensation silicones
They have near ideal elasticity with adequate tear resistance and setting characteristics
The use of the light body and putty enables accurate impressions to be recorded
Dimensional stability is greater than condensation silicones
Also inherently hydrophobic therefore a dry field is required during impression recording
Although surface active agents have been added to newer materials to make it less hydrophobic

17. Silicones Addition silicone impression material
Handling characteristics similar to condensation silicone
Routinely used for crown and bridge impressions
Preferred to condensation silicones due to its dimensional stability.

18. Silicones Addition silicone impression material
Advantages
Disadvantages
Excellent dimensional stability
Hydrogen gas release
Good tear strength
Inhibition of setting by sulphur containing materials
Good working and setting time
Expensive
Excellent wettability
Stiff
Automix system

19. Silicones Addition silicone impression material

20. Polyethers Also supplied as two pastes and automix
Examples: Impregum F, Permadyne (3M ESPE), Polyjel
(Dentsply/Caulk)
McCabe and Walls, 2008

21. Polyethers
Tear resistance and elasticity approaching that of silicones
Relatively rigid when set
It is dimensionally stable under relatively low humidity conditions
The set material is hydrophilic and absorbs moisture under high humidity conditions
Can record accurate impression even when perfect moisture control is not achieved

22. Polyethers
The major disadvantage is its rigidity during its set state- but this is also an advantage , e.g. when taking impressions for implants
Advantages
Disadvantages
Excellent wettabillity
Poor tear strength
Good dimensional stability
Short working and setting time
Stiff
Difficult to disinfect
Expensive
Patient sensitivity

23. Polyethers

24. Comparison of the properties of elastomeric impression material
McCabe and Walls, 2008

25. End of Part 1