[Dental Biomaterials]Impression Materials(TANTA)_American Corner Family 'October 22nd,2010' [ACFF @AmCoFam]

8/8/2019 [Dental Biomaterials]Impression Materials(TANTA)_American Corner Family 'October 22nd,2010' [ACFF @AmCoFam]

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o Uses

Make an accurate replica of

tissues.o Impression

Single tooth.

Whole dentition.

Partially or

completely

edentulous mouth.









• 1-Biocompatible: non toxic- non irritant.

o 2-Acceptable to the patient: pleasant

odour, taste, esthetic colour.

o 3-Ease of manipulation, reasonable

cost.

o 4-Reasonable setting time.

o 5-Adequate shelf life.

o 6-Adequate strength: not tear or break



o 7-Compatible with model materials.

o 8-Dimensionally stable: neither expands

nor contracts.

o 9-Adequate flow properties: to register

fine details.

o 10-Readily disinfected without loss of

accuracy.



Elastic Non Elastic

Non

Elastic





Sets by a physical

reaction due to

temperature

changes

Sets by achemical reaction.

Reversible

Irreversible





Impre

ssion

Ma

terials

Non-elastic

Elastic

Aqueous

Hydrocolloids

Non-aqueous

Elastomers

Polysulfide

Silicones

Polyether

Condensation

Addition

Agar (reversible

Alginate (irreversible

Plaster

Compound

ZnO - Eugenol

Waxes

O’Brien Dental Materials & their Selection



o Thermoplastic material.

o Composition:

Natural resins e.g., shellac & carnuba

wax.

Fillers: soap or talc.

Lubricants: stearic acid.

Colouring agent: e.g., rouge.







Type I: Type I: low fusing compoundlow fusing compound softens at 53-softens at 53-60°C60°C

Supplied in the form of sheets, or cakesSupplied in the form of sheets, or cakes

used as:used as: impression for edentulous patients.impression for edentulous patients.

OrOr in the form of sticks or cones orin the form of sticks or cones or

cylinders.cylinders.Used as:Used as: impression for a single toothimpression for a single tooth

preparation as in (crowns), known aspreparation as in (crowns), known as

Copper Band ImpressionCopper Band Impression..





Type II: Type II: High fusing compoundHigh fusing compound softens atsoftens at

70°°C.70°°C.

Used as tray material to hold a secondaryUsed as tray material to hold a secondaryimpression materialimpression material

Heating:Heating:

o In a water bath-soaking in water in casesIn a water bath-soaking in water in casesof sheets and cakes.of sheets and cakes.

o Over a flame in case of sticks.Over a flame in case of sticks.

o Avoid over heating.Avoid over heating.o KneadingKneading: with the fingers.: with the fingers.

o Importance: assures uniform heatingImportance: assures uniform heating

Increases the flow.Increases the flow.

Gives workability.Gives workability.

















Cooling:Cooling:

o Assure uniform cooling byAssure uniform cooling by

spraying with water at 16-18°Cspraying with water at 16-18°C

before removal from the mouth.before removal from the mouth.



Flow:Flow: Type 1 Type 1: 85%: 85% at 45°Cat 45°C

less than 6% atless than 6% at

37°C.37°C.

Type II: Type II: 70% at 45°C70% at 45°C

less than 2% at 37°C.less than 2% at 37°C.

Viscous material does not record fineViscous material does not record fine



• Low thermal conductivity.Low thermal conductivity.

• High expansion and contractionHigh expansion and contraction

coefficients.coefficients.

• Linear contraction on cooling fromLinear contraction on cooling from

mouth temperature to roommouth temperature to room

temperaturetemperature

(0.3%-0.4%).(0.3%-0.4%).



o Dimensional Changes: due to relief of Dimensional Changes: due to relief of

internal stresses (relaxation)internal stresses (relaxation) →→ WarpageWarpage

→→distortion of the impression.distortion of the impression.

o Model should be poured as soon asModel should be poured as soon as

possible.possible.

o No separating medium.No separating medium.

o Separation of model.Separation of model.







Uses:Uses:

Secondary impression or final wash in aSecondary impression or final wash in a

special tray.special tray.

Composition of powder:Composition of powder:1. Calcium sulphate hemihydrate.(main

ingredient)

2. Potassium sulphate or nitrate:

Accelerator

3. Flavouring agent.

4. Colourin a ents.



Reaction:Reaction:

Chemical reaction:Chemical reaction: crystalization andcrystalization and

exothermicexothermic

CaSOCaSO44 ½ H½ H22O + HO + H22OO →→CaSOCaSO44.2H.2H22O + heatO + heat

Dimensional changes:Setting expansion can be reduced to + 0.06%

by presence of K 2SO4.

Soluble impression plaster:

Contains starch to facilitate the separation of

impression from model by softening when



Manipulation:Manipulation:

Water / powder ratio.55 to 60ml water to 100gm of powder.

Separating medium alcoholic solution of

varnish. Or soap suspensions.

Properties.

o Storage problems:

o kept in sealed containers.



Slide 9 of 33



Advantages and

DisadvantagesAdvantages Disadvantages

Accurate

reproduction of fine details

Minimal dimensionalchanges

Patient may

experiencedry sensation

Material is brittle(fracture If undercuts arepresent)



Uses: as a secondary impression, correctivewash.

Composition

1. Base materials

• zinc oxide• Inert oils: mineral oil.

2. Accelerator:

a. Oil of cloves or eugenol.b. Gum rosin.

c. Fillers: talc, kaolin.

d. Accelertor: MgCl2 and moisture.



Other products: NON Eugenol type

Eugenol free: chlorothymol or

carboxylic acid or lauric acid

substituted for eugenol.



Setting reactionSetting reaction

Acid – base reaction.

Zinc oxide + water zinc hydroxide

Zinc hydroxide + 2 eugenol

Acid base

zinc eugenolate (chelate) (salt)

Chelation reaction



Chelation:

Is the attachment of a molecule or ion to

metal atom at more than one point.

The term is derived from the Greek word

meaning “crab’s claw” indicating two pronged

attachment.• A central zinc atom is held by two eugenol

“claws”.



Setting timeSetting time

Types: S.T Type I: hard 10 minutes

Type II: soft 15 minutes

Factors Controlling the setting time:

Accelerators: water, magnesium

chloride, zinc acetate or alcohol.

Retarders: inert oils such as olive oils,

mineral oil.



Ratio of zinc oxide paste to eugenol

paste.

Cooling spatula and mixing slab.

Effect of high temperature and

humidity:

sets more quickly at high temperature



o Manipulation.









Pouring and separating cast.

Dimensional changes:

Shrink less than 0.1% after 30

minutes.

Delayed pouring of impression – tray

should be stable.

o Do not use base plate (shellac) special

tray →warpage on standing →distortion

of impression

Plaster



Im

pres

sion

Materials

Non-elastic

Elastic

Aqueous

Hydrocolloids

Non-aqueous

Elastomers

Polysulfide

Silicones

Polyether

Condensation

Addition

Agar (reversible


Plaster

Compound

ZnO - Eugenol

Waxes




Solution: homogenous mixture:

one phase system.

Suspension: hetrogenous mixture:

two phase system.

Colloids: hetrogenous, particle size of the

particles are smaller than in suspension:

two phase system.

Dispersed phase.

Dispersion medium →water →Hydrocolloid

• Sol stateSol state: viscous liquidviscous liquid



• Sol state:Sol state: viscous liquid.viscous liquid.

• Gel state:Gel state: jelly like jelly like

solsol

→→ fibrils in a network pattern.

→Brush heap structure.Brush heap structure.

•

reversible hydrocolloidreversible hydrocolloid

Or by: chemical reaction:Or by: chemical reaction:

irreversible hydrocolloidirreversible hydrocolloid..

Agglomeration of molecules

SolSol reduction in temperature

gel

gel



Reversible hydrocolloids: Agar-AgarReversible hydrocolloids: Agar-Agar

Liquefaction temperatureLiquefaction temperature: 71°C-100°C.: 71°C-100°C.

Gelation temperatureGelation temperature 37°C-43°C.37°C-43°C.

• Hysteresis:Hysteresis: temperature lag or differenttemperature lag or different

liquefaction and gelation temperatureliquefaction and gelation temperature

• SolSol gel: physicalgel: physical

change.change.



agar hydrocolloid (hot agar hydrocolloid (cold

(sol

cool to 43 C

heat to 100 Cgel



UsesUses

Composition:Composition: AgarAgar 12.5% by wt.(extracted from12.5% by wt.(extracted fromsea weeds)sea weeds)

Borax(strengthener)Borax(strengthener)

Potassium sulphatePotassium sulphate

Alkyl benzoate(anti fungal )Alkyl benzoate(anti fungal )

WaterWater 85.5% by wt.85.5% by wt.

Syringes:Syringes: low viscosity – high flow.low viscosity – high flow.

Tubes: Tubes: high viscosity – heavy body: low flow.high viscosity – heavy body: low flow.



ManipulationManipulation

• Heating and Conditioning BathHeating and Conditioning Bath



Manipulation3chamber conditioning unit

)1(liquefy at 100°C for10 minutes

converts gel to sol

)2(store at 65°C

place in tray

)3(temper at 46°C for 3 minutes

seat tray

cool with water at 13°C for 3

minutes

converts sol to gel

G l tiG l ti U f t li t tU f t li t t



Gelation:Gelation: Use of water cooling system trayUse of water cooling system tray

with means of retention (perforations).with means of retention (perforations).

Avoid iced H2O: concentration of

stresses.

A id ti th t



Avoid exerting pressure on the tray or

moving it.

Removal impression: one single stroke

or sudden pull.

→reduce permanent deformation and

tearing of impression

Dimensional changes:Dimensional changes:



g

Loss of water by EvaporationLoss of water by Evaporation

Synersis:Synersis: Exuding of fluid at surfaceExuding of fluid at surface

of the gel (fibrils cross link continuesof the gel (fibrils cross link continues

..

Imbibition:Imbibition:

If the gel absorbs water If the gel absorbs water

expansion or swelling.expansion or swelling.

Stresses:Stresses:

Pressure on tray during gelation.

Use of iced H2O during initial stages

Shrinkage

Syneresis



60

Syneresis

Imbibition

contract or expand by water loss or gain

H2O

H2O

Ad d



Advantages and

Disadvantages of AgarAdvantages:Detail reproduction is very

good.

Can record undercut areascorrectly.

Distortion on removal isprevented due to elasticrecovery.

Well tolerated by thepatient.

Can be reused.

Disadvantages:Can not be electroplated.

Thin sections of impression

tears easily.Multiple models can not be

poured like elastomericimpression materials.

Special armamentarium

(equipments) required.Gypsum hardener required.

Sterilization of impressionis difficult.



Advantages:Advantages:

Easy to manipulate.

Does not require

special equipment.

Relatively

inexpensive.

Comfortable for the

UsesUsesSolSol gel by chemical reactiongel by chemical reaction



Composition:Composition:

Potassium alginate.(salt of alginic acid)

Calcium sulphate dihydrate.(reactor)

Potassium sulphate.(improves gypsum

surface)

Sodium phosphate: retarder.

Diatomaceous earth: filler.

Glycols: dustless. Pigments.

Flavours.

Quaternary ammonium salts:

i



Reaction:Reaction:

1.1. CaSOCaSO44.2H.2H

22O + NaO + Na33POPO

44

2.2. CaSOCaSO44.2H.2H

22O+k Alginate K O+k Alginate K 22SOSO

44 + calciu+ calciu

alginatealginate

(insolubl(insolubl

gel)gel)

Types:Types: amount of Naamount of Na33POPO44

Fast set: less amount of retarder.

Regular set.

+ H2O CaCa33POPO

44 + 3Na+ 3Na22SOSO

Concentration of filler:Concentration of filler:



Concentration of filler:Concentration of filler:

Controls flexibility of set impression.Controls flexibility of set impression.

Soft set: less amount of filler. Hard set.

Manipulation:

Proportioning.

Mixing: vigorous mix – against sides of

the rubber bowl. Mixing time: 45 seconds (fast set).

One minute (regular set).

G l ti tiG l ti ti



Gelation time:Gelation time:

1.5-5 minutes from the start of mix till1.5-5 minutes from the start of mix till

material is no longer tacky when touchedmaterial is no longer tacky when touched

with finger.with finger.

Avoid movement of the tray during

setting.

Remove the tray after additional/2-3

minutes as elasticity is improved with

time and permanent deformation is ↓↓.

Control of the S T:



Control of the S.T:

• Do not reduce powder/H2O ratio as

this affects consistency, accuracy and

↓strength.• To prolong S.T: reduce temperature

of H2O *not below 18°C.

temperature of water should be

between 18-24°C.

• Better to choose the suitable type of



H t id di i l hHow to avoid dimensional changes



How to avoid dimensional changesHow to avoid dimensional changes

1.Immediate pouring of the impression.

2.Storing in a humidor: 100% relative

humidity or wrapping in paper towel

saturated with water.

• This does not prevent

synersis.

• Done only for one

hour maximum.

Surface Hardness Of The CastSurface Hardness Of The Cast



Surface Hardness Of The CastSurface Hardness Of The Cast

Gypsum casts poured against

hydrocolloids sometimes have rough or

chalky surface which causes inaccuracy

or lack of sharp details.

Causes:Causes:

• Impression not washed from blood or

saliva after removal from the mouth as

blood and saliva retard the setting of

gypsum.

E H O l ft i i i f b f



• Excess H2O left in impression surface before

pouring dilute surface of the model.

• Impression stored in humidor for ½ or 1

hour, not washed to remove exudate.

• Removal of the model after a long time(several hours)…contact of the gel

containing H2O with gypsum which is

slightly soluble. CaSO4.2H2O chalky

surface.

• Premature removal of the model: not before



Syringed agar: boiled for 8 minutes cooledSyringed agar: boiled for 8 minutes cooled

to 65°C for 10 minutes, injected aroundto 65°C for 10 minutes, injected around

preparation.preparation.

Alginate: mixed inAlginate: mixed in

tray over agar.tray over agar.

Setting time: 4Setting time: 4

minutes.minutes.

Ad tAd t



Advantages:Advantages:

• Simple heating equipment.Simple heating equipment.

• No water cooling system trays.No water cooling system trays.

• Fine details of preparation.Fine details of preparation.

• Agar: more compatible with gypsumAgar: more compatible with gypsum

model materials than alginate, & hasmodel materials than alginate, & has

higher tear strength than algiantehigher tear strength than algiante

Plaster



Impression

Materia

ls

Non-elastic

Elastic

AqueousHydrocolloids

Non-aqueous

Elastomers

Polysulfide

Silicones

Polyether

Condensation

Addition

Agar

(reversible


Compound

ZnO - Eugenol

Waxes




Rubber-like in nature *polymers.

ADA No. 19: Non Aqueous Elastomers

Uses:

• Impression for crown and bridge.

• Partial denture.



Non-Aqueous Elastomers• Synthetic rubbers

• mimic natural rubber• scarce during World War II

• Large polymers

• some chain lengthening• primarily cross-linking

• Viscosity classes• low, medium, high, putty

• monophasic

Phillip’s Science of Dental Materials

I- PolysulphidesI- Polysulphides



I PolysulphidesI Polysulphides

BaseBase CatalystCatalyst

• Polysulphide polymer • Lead

dioxide.

•Dibutylphthalate

• Sulphur

• Copper carbonate

Titanium carbonate

Or silica as filler materials.



Polymer with terminal and pendant mercaptan groups (-SH(

Byproduct H2O

Reaction: condensation polymerizationReaction: condensation polymerization



Reaction: condensation polymerizationReaction: condensation polymerization

Terminal and pendant gps of polymer are

oxidized by lead dioxide →chain extension of

terminal SH gp and cross linking of pendant

gp.

Polysulphide polymer + lead dioxide →

polysulphide rubber + lead oxide + H2O …..

Exothermic 3-4°C.

↑↑ in molecular weight

Paste → rubber.

Base: three consistenciesBase: three consistencies



Base: three consistenciesBase: three consistencies

low: syringe ------ light body

Medium ----------- regular

High: tray ----------- Heavy body

As % filler

increase

viscosity

increase

s



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

SH

HS-

-

S

H

O=

Pb

=

O

O=

Pb

=

OO = Pb =

OHS

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

S

S

+3PbO + H2O

mercaptan + lead dioxide polysulfide rubber + lead oxide +water






Lead dioxide: is dark brown to

gray brown in colour and toxic.

So substituted by hydrated

Cu(OH)2

→green mix

Sili i i t i l



Silicone impression material

I- Condensation SiliconeI- Condensation Silicone

Polymer: hydroxy-terminated polyPolymer: hydroxy-terminated poly

(dimethyl siloxane)(dimethyl siloxane)

BaseBase CatalystCatalyst



Dimethyl siloxane polymer withDimethyl siloxane polymer with

terminal OH gpterminal OH gp

Copper carbonate, silica as fillers.Copper carbonate, silica as fillers.

Stannous octoate + alkylStannous octoate + alkyl

silicate assilicate as

Tetra ethyl silicate Tetra ethyl silicate

ReactionReaction →→ silicone rubber + alcoholsilicone rubber + alcohol

exothermicexothermic 1°C1°CCondensation polymerizationCondensation polymerization →→ largestlargest

dimensional change.dimensional change.

ShrinkageShrinkage -0.6%-0.6%

ConsistenciesConsistencies: only two: only two

LowLow putty very highputty very high

Limited shelf life due to oxidation of stannousLimited shelf life due to oxidation of stannous

octoate and ethyl silicate is not stable in presenceoctoate and ethyl silicate is not stable in presence

++



Hydroxyl terminated polydimethyl

siloxane

Crosslinking reaction

Tin compound





Vinyl terminated polydimethyl siloxane

Crosslinking reaction (no byproduct(



Reaction:Reaction: Ionic PolymerizationIonic Polymerization

Addition type --- no by products.Addition type --- no by products.

If proper balance between two polymers isIf proper balance between two polymers is

not maintainednot maintained →→ 22ryry reaction occurs.reaction occurs.

EvolutionEvolution of the hydrogen gasof the hydrogen gas

→→ bubbles on surface of bubbles on surface of

impressionimpression →→

voids in stone model.voids in stone model.

∴∴ Manufacturers add finely dividedManufacturers add finely divided PlatiniumPlatinium

oror palladiumpalladium to absorbto absorb Hydrogen.Hydrogen.

C i t iC i t i ll didi hi hhi h



Consistencies:Consistencies: lowlow mediummedium highhigh

lightlight regularregular heavyheavy

and a very high (putty).and a very high (putty).

Latex or rubber gloves: containing

sulphur → cause retarded or no

polymerization of addition silicones Use: Vinyl gloves.

IV- Polyethers:IV- Polyethers:



IV Polyethers:IV Polyethers:

BaseBase

Polymer with ethylenePolymer with ethyleneImine rings terminalImine rings terminal

groups.groups.

Silica fillerSilica fillerplasticizer: glycoetherplasticizer: glycoether

phthalatephthalate

CatalystCatalyst

Cross linking agentCross linking agentas dichlorobenzeneas dichlorobenzene

sulphonatesulphonate

Reaction:Reaction:

Cationic polymerization and opening of the iminerings.

Additional polymerization

exothermic 4°C



Structure of polyether

crosslinking reaction with imine end groups

No byproduct

Consistencies: *medium consistency + thinner



Consistencies: medium consistency + thinner

in a separate tube to ↓↓viscosity.

Recently low and high viscosity.

Hydrophilic must not be stored in H2O or

humid atmosphere.

Very short working time 2.5 minutes

↑↑by thinner

Stiff: difficult to remove from the patient’s

mouth and to separate from the cast.

Properties of elastomeric impressionProperties of elastomeric impression



materialsmaterials

Setting timeSetting time

Polysulphide: longest S.T 7-10 min.

↓Condensation silicone 6-8 min.↓Addition silicone 6-8 min.

↓Polyethers 3-4.5 min.

W.T and S.T Decreases as viscosity increases from

low to high

W.T and S.T ↓↓ b ↑↑ in tem erature and

Dimensional Changes on SettingDimensional Changes on Setting



Dimensional Changes on SettingDimensional Changes on Setting

Addition silicone: smallest change

-0.15%

Polyethers -0.2%

Polysulphides -0.4%

Condensation silicone: largest change

-0.6%

Causes of dimensional



Causes of dimensional

changes:Continuation of the polymerization rxn

Thermal contraction

Volatile components

Elastic Recovery from Deformation:Elastic Recovery from Deformation:



yy

Addition silicone: shows the best recovery

from deformation↓Condensation silicone.

↓Polyethers

↓Polysulfies shows greatest deformation

i.e., poorest recovery.

Visco elasticVisco elastic

Mechanical properties are time dependent,

higher rate of deformation → higher tear

strength (sudden pull).



Detail Reproduction:Detail Reproduction:

All reproduce 0.02mm wide line except

the very high viscosity 0.075mm line.

Compatible with gypsum.

St i i iSt i i i



Strain in compressionStrain in compression

Measure of flexibility.Low consistency more flexible than high

consistency.

Polyethers highest stiffness

Addition silicone

Condensation silicone

Polysulfides lowest

Lowest strain(flexibility)

Highest strain

Shore A HardnessShore A Hardness



Shore A HardnessShore A Hardness

Highest: polyethers.

Lowest: polysulfides

Hardness and flexibility (strain) affect

the force necessary for removal of

impression from mouth.

Tear strength:Tear strength: withstand tearing in thin



Tear strength: Tear strength: withstand tearing in thin

interproximal areas.

Much higher than hydrocolloids 350-700

g/cm.

Elastomers:Elastomers: 2000-4000g/cm.

Polysulfides:Polysulfides: shows the highest tear

strength.

But due to high permanent deformation

→ inaccurate impression



Double mix technique-single impression

• Syringe or light bodied material is

injected in and around preparation.• Heavy body is mixed, inserted in tray

and placed over syringed material.

Two materials bond, set at about the

same time.





1- Automatic mixing systems (mixing

gun).

Advantages



• Uniform dispensing of catalyst and

base.

• Fewer bubbles.

• Less waste than in hand mixed.



2- Hydrophilic Addition Silicone:

Hydrophobic materials has poor

wettability: high contact angle: casts with

voids (water repellent).

In hydrophilic: surfactants (wetting

agents) added → ↓↓contact angle, improve

wettability, simplify pouring of gypsummodels.

Di d b l l d



Disadvantage: cannot be electroplated as

metallizing powder does not adhere to

surface of hydrophilic silicone.

3-Addition Silicone Containing Hydrogen

Absorbers

So that dies can be poured as

soon as desired without bubbles.

4 Single viscosity (Monophase) addition



4- Single viscosity (Monophase) addition

silicone with sufficient shear thinning

qualities

So they can be used as both syringe and

tray material.

Decrease in viscosity at high shear stress

as during syringing or mixing, highviscosity at low stress as when inserted

in the tray.



Documents

[Dental Biomaterials]Impression Materials(TANTA)_American Corner Family 'October 22nd,2010' [ACFF @AmCoFam]