DEFINITION

“An impression is essentially a

negative or reverse replica of any

entity. In dentistry, this replica is of

the teeth and its supporting and

surrounding structures.”

According to the ability of the set According to the ability of the set material to be material to be

withdrawn over undercuts :withdrawn over undercuts :

Elastic impression materials Non-elastic or Rigid

impression materials

AgarAlginate

Impression

compound ZOE

Hydrocolloid

RubbersPolysulfide. Poly silicones. Polyether.

Ideal Requirements of Ideal Requirements of Impression MaterialsImpression Materials

Ideal Requirements of Ideal Requirements of Impression MaterialsImpression Materials

1.1. Fluid enough to adapt to the oral Fluid enough to adapt to the oral

tissuestissues

2.2. Viscous enough to be contained Viscous enough to be contained

in the trayin the tray

3.3. In mouth should transform (set) In mouth should transform (set)

into a rubbery or rigid solid in a into a rubbery or rigid solid in a

reasonable amount of time: reasonable amount of time:

setting time less than 7minsetting time less than 7min

• Set impression should not distort Set impression should not distort or tear when removed from mouthor tear when removed from mouth

• Impressions must be Impressions must be dimensionally stable until the cast dimensionally stable until the cast can be pouredcan be poured

Impression should maintain Impression should maintain

dimensional stability after removal of dimensional stability after removal of

cast to enable making of a second or cast to enable making of a second or

third cast from same impressionthird cast from same impression

BiocompatibleBiocompatible

Material associated, processing Material associated, processing

equipment, and processing time equipment, and processing time

should be cost effectiveshould be cost effective

Elastomers Elastomers or or

Rubber base Impression materials Rubber base Impression materials fulfills most of thesefulfills most of these

Soft and rubber-like & are known Soft and rubber-like & are known

as elastomers or synthetic rubbers.as elastomers or synthetic rubbers.

As per ADA Sp. No. 19 they are As per ADA Sp. No. 19 they are

called as - non-aqueous called as - non-aqueous

Elastomeric dental impression Elastomeric dental impression

materials.materials.

Liquid polymers which are converted Liquid polymers which are converted

into solid rubber at room temperature into solid rubber at room temperature

Contains large molecules with weak Contains large molecules with weak

interaction between them, tied together interaction between them, tied together

at certain points and form 3D networkat certain points and form 3D network

Basically used for dentulous cases Basically used for dentulous cases

by virtue of their ability of by virtue of their ability of

withdrawal from under cuts and withdrawal from under cuts and

their excellent surface detail their excellent surface detail

reproduction.reproduction.

Types:

I. According to chemistry ( setting

rxn)

1) Polysulfides

2) Polysilicones – condensation

& addition

3) Polyether

2. According to Viscosity

1) Light body or syringe

consistency

2) Medium or regular body

3) Heavy body or tray

consistency

4) Very heavy body or putty

consistency

3. ADA ClassificationBased on selected elastic properties & dimensional changes

1) Type I

2) Type II

3) Type III

General Properties:General Properties:

Excellent reproduction of Excellent reproduction of

surface details surface details

Generally hydrophobic (except Generally hydrophobic (except

poly ether)poly ether)

Good elastic properties Good elastic properties

(repeated pouring is possible)(repeated pouring is possible)

Dimensional inaccuracies are Dimensional inaccuracies are

lower but exists due to various lower but exists due to various

reasonsreasons

Excellent tear strength.Excellent tear strength.

Extended shelf-lifeExtended shelf-life

Generally higher costGenerally higher cost

Requires tray adhesive or Requires tray adhesive or

mechanical interlocking with the mechanical interlocking with the

tray.tray.

CHARACTERSTICSCHARACTERSTICS

Rheological properties Rheological properties

(viscoelastic )- play major role(viscoelastic )- play major role

Introduced as Viscous pastes- Introduced as Viscous pastes-

setting reaction- viscoelastic setting reaction- viscoelastic

solids.solids.

imp. Mat. should be free of any imp. Mat. should be free of any

distortion dev due to strain during distortion dev due to strain during

its removal, thus the mat. Should its removal, thus the mat. Should

be visco elastic i.e. intermediate be visco elastic i.e. intermediate

behavior between elastic solid and behavior between elastic solid and

viscous liquid.viscous liquid.

• All elastomers - two paste systems (base & catalyst)

• Putty consistency – supplied in jars

Supplied as:

Uses:

Impression material for all applications

including

Fixed partial dentures

Dentures and edentulous impressions

Border molding of special trays (poly ether)

Bite registration

As duplicating material for refractory casts

1.1. POLY SULFIDES:POLY SULFIDES:

IIstst elastomer to be introduced elastomer to be introduced

mercaptan/Thiokol mercaptan/Thiokol

PolysulfidePolysulfide

First dental elastomersFirst dental elastomers IndicationsIndications

complete denturecomplete denture removable fixed partial dentureremovable fixed partial denture

tissuetissue

crown and bridgecrown and bridge

Composition:

Base Paste:

Liquid Polysulfide Polymer - 80 to 85 %

Inert fillers (Titanium dioxide, zinc sulfate ,copper carbonate or silica)

16 to 18 %Plasticizer-- dibutylpthalate (viscosity)

Accelerator--- 0.5% Sulfur

Reactor /catalyst/accelerator Paste

Lead dioxide - 60 to 68 %

Dibutylphthalate (plasticizer) - 30 to 35 %

Sulfur (accelerator) - 3 %

Retarder --- oleic acid or stearic acid

Other substances like Magnesium

& deodorants- 2 %

Tray adhesive:

Butyl rubber or

styrene/acrylonitrile dissolved in a

volatile solvent such as chloroform

or a ketone.

Chemistry and Setting ReactionsChemistry and Setting Reactions

The lead dioxide reacts with the poly sulfide The lead dioxide reacts with the poly sulfide

polymer polymer

Oxidizing agent like lead dioxide initiates Oxidizing agent like lead dioxide initiates

polymerization rxn throughpolymerization rxn through

Chain lengthening by oxidation of the Chain lengthening by oxidation of the

terminal -SH groups andterminal -SH groups and

Cross-linking between pendant -SH groups.Cross-linking between pendant -SH groups.

Exothermic reaction - 3 to 4Exothermic reaction - 3 to 400 C C rise in temp. leaving water as by rise in temp. leaving water as by product.product.

It is accelerated by heat and It is accelerated by heat and moisture moisture

PbOPbO22 + S + S

HS - R- SH HS - R- SH HS - R-S-S-R-SH HS - R-S-S-R-SH

+ H+ H22OO

Mercaptan + Lead dioxide Mercaptan + Lead dioxide Poly sulfide Poly sulfide +Water +Water

T-butyl hydro peroxide – alternative to PbO2

--SH HS---------------------SH HS--

S H

O

=

Pb

=

O

O

=

Pb

=

OO = Pb = OH

S

-S-S---------------S-S-

S

S

+ 3PbO + H2O

mercaptan + lead dioxide polysulfide rubber + lead oxide + water

Polysulfide ReactionPolysulfide Reaction

O’Brien Dental Materials & their Selection 1997

1. Unpleasant odor and colour - stains linen & messy to work with

2. Extremely viscous and sticky - mixing is difficult

3. Mixing time is 45 seconds 4. Long setting time of 12.5 (at 370C) - Patient

discomfort5. Excellent reproduction of surface detail

Properties:

Dimensional stability:

- Curing shrinkage is high 0.45%. It has the highest permanent

deformation (3 to 5%) among the elastomers

It is hydrophobic - so the mouth should be dried thoroughly before making an impression

The shelf life is good (2 years)

AdvantagesAdvantages

Lower costLower costcompared to silicones and compared to silicones and

polyetherspolyethersLong working timeLong working timeHigh tear strengthHigh tear strengthHigh flexibilityHigh flexibilityGood detail reproductionGood detail reproduction

Phillip’s Science of Dental Materials 1996

DisadvantagesDisadvantages

Poor dimensional stabilityPoor dimensional stabilitywater by-productwater by-productpour within one hourpour within one hoursingle poursingle pour

Custom traysCustom trays MessyMessy

paste-paste mixpaste-paste mixbad odorbad odormay stain clothingmay stain clothing

Long setting timeLong setting time

Phillip’s Science of Dental Materials 1996

Silicone Rubber Silicone Rubber Impression Material:Impression Material:

Developed to over come some of the Developed to over come some of the

disadvantages of poly sulfidedisadvantages of poly sulfide

Based on the type of

polymerization reaction

1) Condensation

silicones

2) Addition silicones

Types

• Also known as conventional silicone.

• Available in light, medium and putty consistency

CONDENSATION SILICONE:

IndicationsIndications

complete denturescomplete dentures

crown and bridgecrown and bridge

Base Base pastepaste Accelerator pasteAccelerator paste

Polydimethyl siloxanePolydimethyl siloxane

(hydroxyl-terminated)(hydroxyl-terminated)

Tetraethyl Tetraethyl Orthosilicate – (cross Orthosilicate – (cross linking agent)linking agent)

Colloidal silica or Colloidal silica or microsizedmicrosized metal metal oxide (filler) 35-75%oxide (filler) 35-75%

Stannous octoate – Stannous octoate – (catalyst)(catalyst)

Color pigmentsColor pigments

COMPOSITION:

CHCH33 OCOC22HH55

OH-Si-OH + COH-Si-OH + C22HH55O-Si- OCO-Si- OC22HH55

Sn Sn octoate octoate

CHCH33 OC OC22HH55SiliconeSilicone

+ CH+ CH33CHCH22OHOH

Cross-linking between terminal group of the Cross-linking between terminal group of the silicon polymers and alkyl silicate to form 3D silicon polymers and alkyl silicate to form 3D networknetwork

SETTING REACTION:

Dimethyl + Tetraethyl Dimethyl + Tetraethyl orthosilicateorthosilicate

siloxanesiloxane Stannous octateStannous octate

Silicone Silicone + + ethyl ethyl rubber alcoholrubber alcohol

Ethyl alcohol – byproduct-evaporate -shrinkage &dimensional instability

Tray adhesive –

Polydimethyl siloxane & Ethyl silicate

Properties:• Pleasant odor and color.

• Mixing time of 45sec & setting time of

8-9mins.

• Excellent reproduction of surface

details and highly elastic.

• Lesser dimensional stability

- high curing shrinkage (0.4 -

0.6%)

permanent deformation due to

shrinkage caused by the

evaporation of ethyl alcohol is also

high (1-3%).

Hydrophobic - needs a dry field..

Biologically inert.

Compatible with all gypsum

products.

AdvantagesAdvantages

Better elastic propertiesBetter elastic properties

Clean, pleasantClean, pleasant

Stock trayStock trayputty-washputty-wash

Good working and setting timeGood working and setting time

DisadvantagesDisadvantages

Poor dimensional stabilityPoor dimensional stabilityhigh shrinkagehigh shrinkage

polymerizationpolymerizationevaporation of ethanol evaporation of ethanol

pour immediatelypour immediatelywithin 30 minuteswithin 30 minutes

HydrophobicHydrophobicpoor wettabilitypoor wettability

Addition silicones:Addition silicones:

Also called as polyvinyl siloxanesAlso called as polyvinyl siloxanes

Better properties than condensation silicones.Better properties than condensation silicones.

IndicationsIndications

crown and bridgecrown and bridgedenturedenturebite registrationbite registration

-Improvement over condensation -Improvement over condensation siliconessilicones

-no by-product-no by-product

Base: Poly (methyl hydrogen siloxane) Other siloxane prepolymers Fillers

Composition:

Accelerator:

Divinyl poly siloxane Other siloxane pre polymers Platinum salt: Catalyst

(chloroplatinic acid) Palladium (Hydrogen absorber) Retarders Fillers

CHCH33 CHCH33 CHCH3 3 CHCH33

Pt saltPt salt

Si-H + CHSi-H + CH22=CH-Si =CH-Si Si-CH Si-CH22-CH-CH22-Si-Si

activatoractivator

CHCH33 CH CH3 3 CHCH33 CH CH33

Vinyl + Silane Vinyl + Silane SiliconeSiliconesiloxane siloxane siloxane siloxane rubberrubber

SETTING REACTION:

No by product, but imbalance hydrogen gas air bubbles in the stone models

To avoid this palladium /platinum is added.

CLINICAL SIGNIFICANCE:

Sulfur compounds retard the setting of

silicones

One source of sulfur contamination is

from latex gloves

Vinyl gloves should be used

Properties:• Pleasant odor and color

• Excellent reproduction of surface

details

• Mixing time of 45 secs ,setting time of

5-9 mins.

• Best dimensional stability

- low curing shrinkage (0.17 %)

- lowest permanent deformation (0.05 – 0.3 %)

Stone pouring delayed by 1-2 hoursExtremely hydrophobic, some

manufacturers add a surfactant (detergent) to make it more hydrophilic

Good shelf life of 1-2 yrsGood tear strength (3000gm / cm2)

AdvantagesAdvantages

Highly accurateHighly accurateHigh dimensional stabilityHigh dimensional stability

pour up to one weekpour up to one weekStock or custom traysStock or custom traysMultiple castsMultiple castsEasy to mixEasy to mixPleasant odorPleasant odor

DisadvantagesDisadvantages

ExpensiveExpensiveSulfur in latex gloves + ferric and Sulfur in latex gloves + ferric and

Al sulfate in retraction solutionAl sulfate in retraction solution

inhibits settinginhibits setting

Polishing teeth with pumice req Polishing teeth with pumice req before impression.before impression.

Short working timeShort working time

Lower tear strengthLower tear strength

Possible hydrogen gas releasePossible hydrogen gas releasebubbles on diebubbles on die

palladium or platinum salts added to palladium or platinum salts added to

absorb gases and act as scavengerabsorb gases and act as scavenger

Addition SiliconesAddition Silicones

Surfactants addedSurfactants added reduce contact anglereduce contact angle improvedimproved

castabilitycastabilitygypsumgypsum

wettability?? wettability?? still need dry field clinicallystill need dry field clinically

Pratten J Dent Res 1987 Mandikos Aust Dent J 1998

Poly ether Rubber Poly ether Rubber Impression materialImpression material

Introduced in Germany in late Introduced in Germany in late 1960’s 1960’s

Good mechanical properties and Good mechanical properties and dimensional stability, but short dimensional stability, but short working time, very stiff material and working time, very stiff material and expensive expensive

Composition:

Base Paste

Poly ether polymer

Colloidal silica (filler)

Glycol ether or phthalate

(plasticizer)

Accelerator paste

Aromatic sulfonate ester (cross-linking agent)

Colloidal silica (filler) Phthalate or glycol ether (plasticizer)

Available as 3 viscosities: light, medium & heavy bodied.

CHEMISTRY & SETTING CHEMISTRY & SETTING REACTIONREACTION

H O O H H O O H

CHCH3 3 – C - CH– C - CH2 2 – C – O – R – O – C - CH– C – O – R – O – C - CH2 2 – C - CH + – C - CH + Crosslinked Crosslinked

rubberrubber N N N N

CHCH22-CH-CH22 CH CH22-CH-CH22

Polyether + Sulfonic ester Polyether + Sulfonic ester Crosslinked rubber Crosslinked rubber

Exothermic reaction Exothermic reaction 4-5 4-500 C C

Properties:

1. Pleasant odor and taste

2. Mixing time is 30 secs, setting time of

8 mins

3. Dimensional stability is very good.

Curing shrinkage is low (0.24%)

The permanent deformation is

also low (1-2%).

Very stiff (flexibility of 3%), needs extra space,

around 4 mm is given. 5. Hydrophilic (moisture control

not critical) 6. Shelf life extends upto 2 years

AdvantagesAdvantages

Highly accurateHighly accurateGood dimensional stabilityGood dimensional stabilityStock or dual-arch traysStock or dual-arch traysGood surface detailGood surface detailPour within one weekPour within one week

kept drykept dryMultiple castsMultiple castsGood wettabilityGood wettability

DisadvantagesDisadvantages

ExpensiveExpensiveShort working timeShort working timeRigidRigid

difficult to remove from undercutsdifficult to remove from undercutsBitter tasteBitter tasteLow tear strengthLow tear strengthAbsorbs waterAbsorbs water

changes dimensionchanges dimension

AUTOMATIC DISPENSING & MIXING DEVICES

ADVANTAGES:

- More uniform mix

- Less air bubbles

- Reduced working time

Different methods of making impressions

1. Single mix or mono-phase technique:

- Regular viscosity elastomer is used (addition silicone/polyether)

- Paste is mixed, part of it is loaded on to the tray & the

remaining onto the syringe

- Syringe material is injected onto the prepared area & tray material is seated over it.

Multiple mix

technique

DISADV: Higher viscosity material may displace more fluid wash material

RELINE OR 2-STAGE PUTTY WASH TECHNIQUE

• Preliminary impression is made with a putty

consistency using a thin plastic sheet or spacer

over it (acts as a spacer)

• Light body is injected around the prepared

tooth

• The plastic sheet is removed & putty

impression is seated back

ELASTOMERIC IMPRESSION ELASTOMERIC IMPRESSION MATERIALS: MATERIALS: PROPERTIESPROPERTIES

WORKING AND SETTING TIMESWORKING AND SETTING TIMESWorking time- begins at the start of Working time- begins at the start of

mixing and ends just before the elastic mixing and ends just before the elastic properties have developedproperties have developed

Setting time- time elapsing from the Setting time- time elapsing from the beginning of mixing until the curing has beginning of mixing until the curing has advanced sufficiently so that the advanced sufficiently so that the impression can be removed from the impression can be removed from the mouth with a minimum of distortionmouth with a minimum of distortion

Increase in temperature- accelerates Increase in temperature- accelerates

curing timecuring time

Increase in viscosity- decrease in working Increase in viscosity- decrease in working

and setting timeand setting time

Dimensional stabilityDimensional stability

1.1. Polymerization shrinkagePolymerization shrinkage

2.2. Loss of byproductLoss of byproduct

3.3. Thermal contraction from oral to room Thermal contraction from oral to room temperaturetemperature

4.4. ImbibitionImbibition

5.5. Incomplete recovery of deformation Incomplete recovery of deformation because of viscoelastic behavior because of viscoelastic behavior

Reproduction of oral detailReproduction of oral detail

The rubber impression materials are The rubber impression materials are

capable of reproducing detail more capable of reproducing detail more

accurately than can be transferred accurately than can be transferred

to the stone die or castto the stone die or cast

ELASTICITYELASTICITY

Elastic properties of elastomeric impression Elastic properties of elastomeric impression materials improve with an increase in materials improve with an increase in curing time in the mouthcuring time in the mouth

Permanent deformation following strain in Permanent deformation following strain in compression increases in following order- compression increases in following order- addition silicone, condensation silicone, addition silicone, condensation silicone, polyether and polysulfidepolyether and polysulfide

Tear strengthTear strength

Measures the resistance to fracture of Measures the resistance to fracture of elastomeric material subjected to a tensile elastomeric material subjected to a tensile force acting perpendicular to a surface force acting perpendicular to a surface flawflaw

Biocompatibility Biocompatibility

Polysulfide- lowest cell death countPolysulfide- lowest cell death count

Polyether- highest cell toxicityPolyether- highest cell toxicity

Elastomeric Impression Elastomeric Impression MaterialsMaterials

Rapidly removeRapidly removedecreases decreases

permanent permanent deformationdeformationchains recoil from chains recoil from

a recoverable a recoverable distancedistance

increases tear increases tear strengthstrength

Phillip’s Science of Dental Materials 1996

Comparison of PropertiesComparison of Properties

Working timeWorking timelongest to shortestlongest to shortest

agar > polysulfide > silicones > alginate agar > polysulfide > silicones > alginate = polyether= polyether

Setting timeSetting timeshortest to longestshortest to longest

alginate < polyether < agar < silicones < alginate < polyether < agar < silicones < polysulfidepolysulfide

O’Brien Dental Materials & their Selection 1997

StiffnessStiffnessmost to leastmost to least

polyether > addition silicone > polyether > addition silicone > condensation silicone > condensation silicone > polysulfide = hydrocolloidspolysulfide = hydrocolloids

Tear strengthTear strengthgreatest to leastgreatest to least

polysulfide > addition silicone > polysulfide > addition silicone > polyether > condensation silicone polyether > condensation silicone >> hydrocolloids>> hydrocolloids

O’Brien Dental Materials & their Selection 1997

CostCostlowest to highestlowest to highest

alginate < agar = polysulfide alginate < agar = polysulfide <condensation silicone < addition <condensation silicone < addition silicone < polyethersilicone < polyether

Dimensional stabilityDimensional stabilitybest to worstbest to worst

addition silicone > polyether > addition silicone > polyether > polysulfide > condensation silicone polysulfide > condensation silicone > hydrocolloid> hydrocolloid Phillip’s 1996

O’Brien Dental Materials & their Selection 1997

WettabilityWettabilitybest to worstbest to worst

hydrocolloids > polyether > hydrocolloids > polyether > hydrophilic addition silicone > hydrophilic addition silicone > polysulfide > hydrophobic addition polysulfide > hydrophobic addition silicone = condensation siliconesilicone = condensation silicone

CastabilityCastabilitybest to worstbest to worst

hydrocolloids > hydrophilic addition hydrocolloids > hydrophilic addition silicone > polyether > polysulfide > silicone > polyether > polysulfide > hydrophobic addition silicone = hydrophobic addition silicone = condensation siliconecondensation silicone

O’Brien Dental Materials & their Selection 1997

Thank you