By

Dr. RASHID HASSAN

Also called as Rubber Base Impression materials.

Elastomers are rubber like material with long chained polymers, slightly crosslinked & coiled having glass transition temperature much lower than room temperatures.

Accepted in dentistry to overcome 2 main problems associated with Hydrocolloids

Poor tear resistance

Poor dimensional stability

INTRODUCTION

Contain large molecules having weak interaction among them.

Tied together at certain points forming 3 dimensional network.

On mixing with a suitable catalyst, liquid polymer is converted into elastic rubber through addition or condensation polymerization reaction.

Stress application (stretching) causes the chains to uncoil and removal of stress relaxes the chains back to entangled state.

INTRODUCTION

1) Excellent reproduction of fine details (especially low viscosity elastomers).

2) Generally hydrophobic (polyether is hydrophilic).

3) Excellent elastic properties but incomplete elastic recovery.

4) High coefficient of thermal expansion.

5) Excellent tear strength.

6) Electroplating can be done (Copper or silver plated)

7) Shelf life is approximately 2 years (cool conditions increases shelf life).

GENERAL PROPERTIES OF ELASTOMERS

8) Dimensional changes occur.

Due to

a) Curing shrinkage.

b) Loss of by products.

c) Incomplete elastic recovery.

d) Amount of filler content

(less filler = more shrinkage)

(More filler = Less shrinkage)

e) Polyether (being hydrophilic) absorbs water & loose soluble plasticizers causes dimensional change.

f) Thermal contraction when transferred from mouth to room temperature.

g) Time of pouring impression.

GENERAL PROPERTIES OF ELASTOMERS

CLASSIFICATIONOF

IMPRESSION MATERIALS

Elastomers are of 3 types

1) POLYSULPHIDE

2) SILICONES

a) Addition Silicones

b) Condensation Silicones.

3) POLYETHERS

a) Light activated polyethers.

b) Chemically activated polyethers.

ELASTOMERS

POLYSULPHIDE

First elastomeric impression material to be introduced.

Alternate names:

a) Thiokol impression material (By the name of first manufacturer)

b) Marcaptan impression material (by chemistry)

c) Vulcanising impression material (by processing terminology)

INGREDIENTS PERCENTAGE FUNCTION

Polysulphide pre polymer with terminal

SH group

74-80% Reactive ingredient forming rubber

Polysulphideprepolymer with

pendant SH group

2% Reduces permanent deformation during

removal from mouth.

Fillers 16% Paste former

Di butyl Phthlate 0.5% Plasticizer

COMPOSITION OF POLYSULPHIDE IMPRESSION MATERIAL

BASE PASTE

INGREDIENTS PERCENTAGE FUNCTION

PbO2 (Lead dioxide) 78% Oxidizing agent causing polymerization

Sulphur 0.5-3.0% Facilitate reaction

Inert oil (oleic oil, stearic acid)

Traces Pate former

Dibutyl phthalate 17% To form paste withPbO2 and Sulphur.

COMPOSITION OF POLYSULPHIDE IMPRESSION MATERIAL

REACTOR/ACCELERATOR PASTE

BIOLOGICAL:

1) Non toxic, non poisonous.

2) Bad odor due to lead dioxide & Marcaptan group.

3) Easy to disinfect (glutaraldeihyde)

RHEOLOGICAL PROPERTIES:

1) Available in variety of viscosities (Light, Regular, Heavy, Putty)

2) Working time = 3-6 min

3) Setting time = 10-20 min.

PROPERTIES OF POLYSULPHIDE IMPRESSION MATERIAL

MECHANICAL PROPERTIES:

1) Highly flexible of all the elastomers.

2) Elastic recovery improves with time (viscoelasticity).

3) High tear strength.

4) Not dimensionally stable

Cast should be poured immediately.

1) Hardness increases by increasing filler content.

PROPERTIES OF POLYSULPHIDE IMPRESSION MATERIAL

POLYSULPHIDE IMPRESSION MATERIAL

ADVANTAGES

1) Longer working time.

2) Highest flexibility.

3) Highest tear strength.

4) Can be electroplated with silver.

5) Long shelf life.

6) Inexpansive as compared to other elastomers.

DISADVANTAGES

1) Unpleasant odor and taste.

2) Long setting time.

3) Dimensional change due to byproduct formation.

4) Cloth staining.

5) Multiple die pouring not accurate.

USED TO RECORD IMPRESSIONS FOR CROWNS,

BRIDGES, INLAYS, ONLAYS AND PARTIAL DENTURES

CONDENSATION SILICONE IMPRESSION MATERIAL

Earlier of the two silicone impression materials to be introduced.

Alternate names:

1) Conventional silicones.

2) Room temperature vulcanizing (RTV) silicones.

INGREDIENTS FUNCTION

Hydroxy terminal polydimethylsiloxane

For undergoing polymerization & cross linking to form rubber.

Fillers (copper carbonate, colloidal silica.

1) Paste former.2) Increases strength.

3) Gives body to the mix.

COMPOSITION OF CONDENSATION SILICONE IMPRESSION MATERIAL

BASE PASTE

INGREDIENTS FUNCTIONS

Tri or tetra functional ethyl silicate. Cross linking agent.

Tin Octate. Catalyst.

Fillers. Paste former.

Color pigments. To distinguish from base paste.

COMPOSITION OF CONDENSATION SILICONE IMPRESSION MATERIAL

REACTOR/ACCELERATOR PASTE

BIOLOGICAL:

1) Non toxic.

2) Acceptable taste and odour.

3) Proper mixing is required to prevent accelerator paste from coming in contact with the oral tissues.

RHEOLOGICAL:

1) Available in all 4 consistencies (L,R,H,P)

2) Flow after 1 hour = 0.09%

3) Mixing time = 1 min

4) Working time =3 min

5) Setting time = 6-10 min

PROPERTIES OF CONDENSATION SILICONE IMPRESSION MATERIAL

MECHANICAL:

1) Elastic recovery = 99.5%

2) Good tear strength.

3) Flexibility is less than Polysulphides.

4) Dimensionally not stable:

Due to

a) Polymerization shrinkage.

b) Incomplete elastic recovery.

c) Thermal contraction on removal from mouth to room temperature.

PROPERTIES OF CONDENSATION SILICONE IMPRESSION MATERIAL

CONDENSATION SILICONE IMPRESSION MATERIAL

ADVANTAGES

1) Adequate working time & setting time.

2) Clean & pleasant odour.

3) No staining.

4) Adequate tear strength.

5) Better elastic properties.

6) Can be electroplated with silver and copper.

DISADVANTAGES

1) Lower flexibility than polysulphides.

2) Poor dimensional stability due to release of by products.

3) Less accuracy if poured immediately.

4) Hydrophobic nature.

5) Poor to adequate shelf life (1-2 years)

6) Slightly expansive.USED TO RECORD IMPRESSIONS FOR CROWNS,

BRIDGES, INLAYS, ONLAYS AND COMPLETE

DENTURES

ADDITION SILICONE IMPRESSION MATERIAL

Introduced later.

Have much better properties than Condensation silicones.

Alternate names:

1) Poly vinyl siloxane.

2) Vinyl poly siloxane.

INGREDIENTS FUNCTIONS

Poly methyl hydrogen siloxane or moderately low molecular weight silicone pre polymer with silane terminal

group

Takes part in the polymerization

reaction

Reinforced fillers (Powdered silica)

• Controls the viscosity of the set

material.• Modifies the

physical properties.

COMPOSITION OF ADDITION SILICONE IMPRESSION MATERIAL

BASE PASTE

INGREDIENTS FUNCTIONS

Poly di methyl vinyl siloxane or moderately low molecular weight

silicone prepolymer with vinyl terminal group

• Main reactive agent• Takes part in the chemical reaction

Reinforced fillers(Powdered silica)

• Pate former• Increases strength

• Gives body to the mixture• Modifies physical properties

• Controls viscosity

Chloroplatinic acid Acts as a catalyst

Low molecular weight liquid polymer • Acts as a retarder• Controls working & setting times

Finely divided platinum or palladium Acts as a scavenger for H2 gas

Colour pigments To distinguish from base paste

COMPOSITION OF ADDITION SILICONE IMPRESSION MATERIAL

REACTOR/ACCELERATOR PASTE

BIOLOGICAL:

1) Highly biocompatible with oral tissues.

2) Acceptable colour and taste.

RHEOLOGICAL PROPERTIES:

1) Available in all 4 consistencies.

2) Various consistencies serve different purpose

E.g.

Putty or heavy body is used for primary impressions

Regular or light body is used for secondary impressions.

1) Addition silicone impression materials exhibit pseudoplastic properties.

PROPERTIES OF ADDITION SILICONE IMPRESSION MATERIAL

MECHANICAL PROPERTIES:

1) Excellent elastic recovery of 99.93%

2) Permanent deformation of 0.07%

3) Tear strength of3500 gm/cm

4) Flexibility is 3%

5) Flow after 1 hour is <0.05%

6) Mixing time is 35-45 sec

7) Working time = 2-3 min.

8) Setting time = 6-8 min.

PROPERTIES OF ADDITION SILICONE IMPRESSION MATERIAL

ADDITION SILICONE IMPRESSION MATERIAL

ADVANTAGES

Records highly accurate impression.

Pleasant to handle.

Acceptable taste.

Shorter setting time.

Excellent elastic recovery.

No elimination of any by products.

Dimensionally stable.

Can be electroplated with silver & copper.

Multiple die pour is possible.

DISADVANTAGES

More expansive with automatic mixing device.

Shorter working time.

May release H2 gas on setting.

Hydrophobic material.

USED TO RECORD IMPRESSIONS FOR

CROWNS, BRIDGES, INLAYS, ONLAYS,

PARTIAL AND COMPLETE DENTURES

POLYETHER IMPRESSION MATERIAL Polyether was introduced in

Germany in 1960.

Commercial names are, Impregum, Remitec, Polyjeletc.

Polyether is available in 3 viscosities (Light, Regular and heavy body)

Dispensed as 3 paste system

1) Base paste.

2) Reactor/Accelerator paste.

3) Modifier (thinner) paste.

INGREDIENTS FUNCTIONS

Imine terminated poly ether or moderately low

molecular weight polyether with ethylene

imine ring as terminal group.

Undergoes cross linking to form rubber

Colloidal silica Fillers

Glycol ether phthallate Plasticizers

COMPOSITION OF POLYETHER IMPRESSION MATERIAL

BASE PASTE

INGREDIENTS FUNSTIONS

Ester derivative of aromatic sulphonic acid.

Cross linking agent.

Colloidal silica. Filler.

Glycol ether phthallate Plasticizer.

COMPOSITION OF POLYETHER IMPRESSION MATERIAL

REACTOR/ACCELERATOR PASTE

BODY MODIFIER PASTE

INGREDIENT FUNCTION

Octyl phthallate (thinner) + 5% methyl cellulose

• It reduces the stiffness / viscosity of the material

• Gives more working time (retarder)

BIOLOGICAL:

1) Non toxic.

2) Non poisonous.

3) Can cause irritation due to presence of aromatic sulphonic acid catalyst in reactor paste.

4) Can cause hypersensitivity in some patients due to presence of ethylene imine rings in base paste.

RHEOLOGICAL:

1) Available in 3 consistencies (L,R & Heavy body)

2) Flow after 1 hour is < 0.03%

PROPERTIES OF POLY ETHER IMPRESSION MATERIAL

MECHANICAL:

1) Elastic recovery =98.9%

2) Permanent deformation is 1.1%

3) Flexibility is low (2%

4) Mixing time is 45 sec to 1 minute.

5) Working time = 2 minutes.

6) Setting time is 3-5 minutes.

7) Good dimensional stability due to

a) Addition polymerization reaction.

b) Less polymerization shrinkage.

PROPERTIES OF POLY ETHER IMPRESSION MATERIAL

POLY ETHER IMPRESSION MATERIAL

ADVANTAGES

Good pseudoplastic properties i.e. same mixture can be used as tray as well as syringe material.

Dimensionally stable.

Less polymerization shrinkage.

No by product formed.

Pour more accurate cats.

Multiple cast pouring is possible.

Cast pouring can be delayed for few hours, even a week.

Long shelf life.

DISADVANTAGES

Very expansive when compared with other elastomers.

High stiffness.

Low tear strength.

Electroplating not easy.

Catalyst can be sensitive to some patients.

Not available in complete range of viscosities.

USED TO RECORD IMPRESSIONS FOR

CROWNS, BRIDGES, INLAYS, ONLAYS,

PARTIAL AND COMPLETE DENTURES

It was introduced in 1988.

Available in 2 viscosities.

Light body supplied in syringes.

Heavy body supplied as tubes

COMPOSITION OF LIGHT ACTIVATED POLYETHER

LIGHT ACTIVATEDPOLY ETHER IMPRESSION MATERIAL

INGREDIENT FUNCTION

Urethane di methacrylate elastomer resin

Visible light curing polyether

Champhorquinone Photo initiator

Di methyl amino ethyl meth acrylate

Photo accelerator

Silicone dioxide Fillers

LIGHT ACTIVATEDPOLY ETHER IMPRESSION MATERIAL

PROPERTIES OF LIGHT ACTIVATED POLY ETHER

• Excellent elasticity.

• It has operator control over the polymerization.

• Infinite working time.

• Short setting time.

• Low volume shrinkage on setting.

• Impression can be stored upto 2 weeks.

MIXING SYSTEMS FOR ELASTOMERS

MIXING SYSTEMS:

3 types of systems are available to mix catalyst and base thoroughly.

1. Static mixing system.

2. Auto mixing system.

3. Dynamic mechanical mixing system.

MIXING SYSTEMS FOR ELASTOMERS

MIXING SYSTEMS FOR ELASTOMERSSTATIC MIXING SSTEM:

1. Impression pastes are dispensed from collapsible tubes.

2. Equal lengths of catalyst and base paste are dispensed on a paper pad.

3. Initial mixing is accomplished with a circular motion.

4. Final mixing is done with broad strokes of spatula.

5. Final mix should be smooth.

6. Mixing is readily accomplished in 45 seconds.

All 4 types of elastomers are available for mixing in this fashion.

MIXING SYSTEMS FOR ELASTOMERSAUTO MIXING SYSTEM:1. Very popular means for

mixing catalyst and base.2. Base and catalyst are in

separate cylinders of plastic cartridge.

3. Cartridge is placed in mixing gun containing 2 plungers.

4. Equal quantities of base and catalyst are forced through static mixing tip.

5. The tip contains stationary internal plastic spiral to fold both the components over each other to get a uniform mix at the end of the tip.

6. The first part of mix should be discarded for a uniform consistency.

7. Mixed material can be extruded directly either into an injection syringe or impression tray.8. Intra-oral injection tips can be placed at the end of static mixing tip.

9. Material left at the tip gets wasted.(1-2mL).3-4 times less waste as compared to hand mix.

Silicones (both addition & condensation) and Poly ethers are

available with this means of mixing.

MIXING SYSTEMS FOR ELASTOMERSDYNAMIC MECHANICAL MIXING SYSTEM:1. Newest system.Catalyst and base are supplied in large plastic bags, housed in a cartridge.2. Cartridge is inserted into the top of mixing machine.3. A new plastic mixing tip is placed on the front.4. On pressing the button, parallel plungers push against the plastic bags, thus opening the bag.5. Material is forced into the dynamic mixing tip.6. Mixing tip differs from that of Automixing. (internal spiral is motor driven i.e. it rotates with speed )

7. Mixing is accomplished by rotation + forward motion of material through spiral.8. Helpful technique for mixing highly viscous materials.(Polyether and addition silicone are available for mixing with this system)9. Advantages are ease of use, speed and thoroughness of mixing.

10. Disadvantage is cost of the system.Slightly more material is retained at the

tip than Auto mixing but still less wastage as compared to hand mixing.

IMPRESSION TECHNIQUES

FOR ELASTOMERS

IMPRESSION TECHNIQUES FOR ELASTOMERS

SINGLE VISCOSITY TECHNIQUE (Monophase):

1. Often taken with medium viscosity material.

2. When forced through impression syringe, the viscosity decreases but when used with tray the viscosity is unaffected.

3. Addition silicones and Poly ethers are well suited for this technique.

IMPRESSION TECHNIQUES FOR ELASTOMERS

DUAL VISCOSITY TECHNIQUE

(Simultaneous or multiple mix technique):

Low consistency (viscosity) material is injected with a syringe into and around the critical areas and a high consistence (viscosity) material is mixed and placed in the tray.

Both materials bind, join and set together.

IMPRESSION TECHNIQUES FOR ELASTOMERS

PUTTY WASH TECHNIQUE:1. 2 step impression

procedure.2. Preliminary impression is

taken in high or putty consistency material before cavity preparation.

3. Cavity is prepared.4. Low consistency material is

syringed into the prepared cavity.

5. Preliminary impression is then reinserted.

6. The low & high consistency materials bind.

7. When low viscosity material sets the impression is removed.

Technique developed for condensation silicone to minimize dimensional

changes.