Elastomeric Impression Materials Part 1 Dr. Noland Naidoo

ElastomericImpression Materials

Part 1

Dr. Noland Naidoo

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

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

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

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

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 polymerSuitable filler (titanium dioxide or lithopone)Plasticizer ( eg. dibutyl phthalate)Sulphur – small amount that enhances reaction ( catalyst)

Polysulphides

The catalyst paste:Lead dioxidePlasticizer- chlorinated parafinApprox same amount of filler as in base pasteOleic or stearic acid- retarders- control the rate of setting

Polysulphides

Must be used with a special trayReasonable tear strength and good elastic propertiesUnpleasant odor and tasteWork well in the presence of moisture- moderately hydrophilicUsed commonly for crown and bridge impressionsCasts should be poured within 24hrs of impression but not immediately as to allow for full elastic recoilReported incidences of allergic reaction to patients sensitive to latexImpressions 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


• 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



Moderate tear strength Poor dimensional stability

Good working time Poor wetability

Good setting time

SiliconesAddition 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)


• 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


• Handling characteristics similar to condensation silicone

• Routinely used for crown and bridge impressions

• Preferred to condensation silicones due to its dimensional stability.



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


Polyethers

Also supplied as two pastes and automix

Examples: Impregum F, Permadyne (3M ESPE), Polyjel

(Dentsply/Caulk)


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

Polyethers

• The major disadvantage is its rigidity during its set state- but this is also an advantage , e.g. when taking impressions for implants


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


End of Part 1

Documents

Elastomeric Impression Materials Part 1 Dr. Noland Naidoo