Elastomeric
Impression Materials
Part 1
Dr. Noland Naidoo
Classification
Plaster
Compound
Non-elastic
Impression
wax
ZnO- Eugenol
Impression
Materials
Aqueous
Hydrocolloids
Elastic
Agar
(Reversible)
Alginate
(Irreversible)
Polysulfide
Condensation
Non-aqueous
Elastomer
Silicones
Addition
Polyether
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 crosslinking
Cross linking form a three-dimensional network
The amount of cross-linking determines the stiffness and
elastic behaviour of the material
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
Classification
Plaster
Compound
Non-elastic
Impression
wax
ZnO- Eugenol
Impression
Materials
Aqueous
Hydrocolloids
Elastic
Agar
(Reversible)
Alginate
(Irreversible)
Polysulfide
Condensation
Non-aqueous
Elastomer
Silicones
Addition
Polyether
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
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)
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
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.
Polysulphides
Advantages
Disadvantages
Good tear strength
Poor dimension stability
Good elasticity
Offensive odor
Low cost
Stains clothing
Long setting time
Polysulphides
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
Silicones
Condensation silicone impression material
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•
•
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•
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
Silicones
Condensation silicone impression material
Advantages
Disadvantages
Moderate tear strength
Poor dimensional stability
Good working time
Poor wetability
Good setting time
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)
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
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.
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
Silicones
Addition silicone impression material
Polyethers
Also supplied as two pastes and automix
Examples: Impregum F, Permadyne (3M ESPE), Polyjel
(Dentsply/Caulk)
McCabe and Walls,
2008
Polyethers
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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
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
Polyethers
Comparison of the
properties of elastomeric
impression material
McCabe and Walls,
2008
End of Part 1