impression materials

Impression MaterialsImpression Materials

Course Date: 5/05 Reviewed/Updated: 10/10Expiration Date: 10/13

Objectives

• Provide general review of types of dental impression materials.

• Provide general information on the physical and handling properties and indications for use of various types of impression materials.

Official Disclaimer

• The opinions expressed in this presentation are those of the author and do not necessarily reflect the official position of the US Air Force or the Department of Defense (DoD).

• Devices or materials appearing in this presentation are used as examples of currently available products/technologies and do not imply an endorsement by the author and/or the USAF/DoD.

Impression Materials• Non-elastic• Elastic

– Aqueous hydrocolloids• Agar• Alginate

– Non-aqueous elastomers• Polysulfide• Silicones

– Condensation– Addition

• Polyether

Indications

• Diagnostic casts– preliminary– opposing

• Indirect reconstruction– fixed– removable

• Bite registration

Giordano, Gen Dent 2000

Elastomeric Impression Materials

• Viscoelastic– physical properties vary

• rate of loading

• Rapidly remove– decreases permanent

deformation• chains recoil from a recoverable distance

– increases tear strength

Phillip’s Science of Dental Materials 1996

Impr

essi

on

Mat

eria

ls

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 1997

Aqueous Hydrocolloids• Colloidal suspensions

– chains align to form fibrils– traps water in interstices

• Two forms– sol

• viscous liquid

– gel• elastic solid

• Placed intra-orally as sol– converts to gel

• thermal or chemical processPhillip’s Science of Dental Materials 1996


• Semi-permeable membranes– poor dimensional stability

• Evaporation• Syneresis

– fibril cross linking continues• contracts with time• exudes water

• Imbibition– water absorption

• swellsPhillip’s Science of Dental Materials 1996

Elastic



Polysulfide

Silicones

Polyether

Condensation

Addition

Agar (reversible)



Reversible Hydrocolloid (Agar)

• Indications– crown and bridge

• high accuracy

• Example– Slate Hydrocolloid (Van R)

Composition• Agar

– complex polysaccharide• seaweed

– gelling agent

• Borax– strength

• Potassium sulfate– improves gypsum

surface

• Water (85%)

agar hydrocolloid (hot) agar hydrocolloid (cold)

(sol) (gel)

cool to 43ºC

heat to 100ºC


Manipulation

• Gel in tubes– syringe and tray material

Manipulation• 3-chamber conditioning unit

– (1) liquefy at 100C for 10 minutes

• converts gel to sol

– (2) store at 65C– place in tray– (3) temper at 46C for 3 minutes– seat tray– cool with water at 13C for 3 minutes

• converts sol to gel


Advantages

• Dimensionally accurate• Hydrophilic

– displaces moisture, blood, fluids

• Inexpensive– after initial equipment

• No custom tray or adhesives• Pleasant flavor• No mixing required


Disadvantages

• Initial expense– special equipment

• Material must be prepared in advanced• Tears easily• Dimensionally unstable

– Must be poured immediately– Can only be used for a single cast

• Difficult to disinfect


Elastic



Polysulfide

Silicones

Polyether

Condensation

Addition

Agar (reversible)



Irreversible Hydrocolloid (Alginate)

• Most widely used impression material

• Indications– study models– removable fixed partial dentures

• framework

• Examples– Jeltrate (Dentsply/Caulk)– Coe Alginate (GC America)


Composition• Sodium alginate

– salt of alginic acid• mucous extraction of

seaweed (algae)

• Calcium sulfate– reactor

• Sodium phosphate– retarder

• Filler• Potassium fluoride

– improves gypsum surface

2 Na3PO4 + 3 CaSO4 Ca3(PO4)2 + 3 Na2SO4

Na alginate + CaSO4 Ca alginate + Na2SO4

(powder) (gel)

H2O

O’Brien Dental Materials & their Selection 1997

Manipulation

• Weigh powder• Powder added to water

– rubber bowl– vacuum mixer

• Mixed for 45 sec to 1 min• Place tray• Remove 2 to 3 minutes

– after gelation (loss of tackiness)

Caswell JADA 1986

Advantages

• Inexpensive

• Easy to use

• Hydrophilic– displace moisture, blood, fluids

• Stock trays


Disadvantages

• Tears easily• Dimensionally unstable

– immediate pour – single cast

• Lower detail reproduction– unacceptable for fixed pros

• High permanent deformation• Difficult to disinfect


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


Elastic



Polysulfide

Silicones

Polyether

Condensation

Addition

Agar (reversible)



Polysulfide

• First dental elastomers• Indications

– complete denture– removable fixed partial denture

• tissue

– crown and bridge

• Examples– Permlastic (Kerr)– Omni-Flex (GC America)

Composition• Base

– polysulfide polymers– fillers– plasticizers

• Catalyst– lead dioxide (or copper)– fillers

• By-product– water


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

S H

O

=

Pb

=

O

O

=

Pb

=

OO = Pb = O

HS

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

S

S

+ 3PbO + H2O

mercaptan + lead dioxide polysulfide rubber + lead oxide + water

Polysulfide Reaction


Manipulation

• Adhesive to tray• Uniform layer

– custom tray

• Equal lengths of pastes• Mix thoroughly

– within one minute

• Setting time 8 – 12 minutes• Pour within 1 hour

Advantages

• Lower cost– compared to silicones and polyethers

• Long working time

• High tear strength

• High flexibility

• Good detail reproduction


Disadvantages• Poor dimensional stability

– water by-product– pour within one hour– single pour

• Custom trays• Messy

– paste-paste mix– bad odor– may stain clothing

• Long setting time


Elastic



Polysulfide

Silicones

Polyether

Condensation

Addition

Agar (reversible)



Condensation Silicone

• Indications– complete dentures– crown and bridge

• Examples– Speedex (Coltene/Whaledent)– Primasil (TISS Dental)

Composition

• Base– poly(dimethylsiloxane)– tetraethylorthosilicate– filler

• Catalyst– metal organic ester

• By-product– ethyl alcohol

Phillip’s 1996


HO – Si – O – Si - O - H

CH3

CH3 CH3

CH3 n

HO – Si – O – Si - O - H

CH3

CH3 CH3

CH3 n

C2H5O OC2H5

Si

C2H5O OC2H5

HO – Si – O – Si - O -

CH3

CH3 CH3

CH3 n

HO – Si – O – Si - O -

CH3

CH3 CH3

CH3 n

OC2H5

Si

OC2H5

+ 2C2H5OH

Condensation Silicone Reaction

metal organic ester

ethanol


Manipulation• Mix thoroughly

– paste - paste– paste - liquid

• Putty-wash technique– reduces effect of polymerization shrinkage– stock tray

• putty placed

• thin plastic sheet spacer

• preliminary impression– intraoral custom tray

• inject wash material

Advantages

• Better elastic properties

• Clean, pleasant

• Stock tray– putty-wash

• Good working and setting time


Disadvantages

• Poor dimensional stability– high shrinkage

• polymerization

• evaporation of ethanol

– pour immediately• within 30 minutes

• Hydrophobic– poor wettability


Elastic



Polysulfide

Silicones

Polyether

Condensation

Addition

Agar (reversible)



Addition Silicones• AKA: Vinyl polysiloxane• Indications

– crown and bridge– denture– bite registration

• Examples– Extrude (Kerr)– Express (3M/ESPE)– Aquasil (Dentsply Caulk)– Genie (Sultan Chemists)– Virtual (Ivoclar Vivadent)

Composition

• Improvement over condensation silicones– no by-product

• First paste– vinyl poly(dimethylsiloxane)

prepolymer

• Second paste– siloxane prepolymer

• Catalyst– chloroplatinic acid

Phillip’s 1996


O

H - Si – CH3

O

CH3 - Si - H

O

---O – Si – CH = CH2

CH3

CH3 CH = CH2 – Si – O ---

CH3

CH3

O

- Si – CH3

O

CH3 - Si -

O

---O – Si – CH2 - CH2

CH3

CH3

CH2 - CH2 – Si – O ---

CH3

CH3

Chloroplatinic Acid Catalyst

Addition Silicone Reaction


Manipulation

• Adhesive to tray

• Double mix– custom tray

• heavy-body

– light-body to prep

• Putty-wash– stock tray

Craig Adv Dent Res 1988

Advantages

• Highly accurate

• High dimensional stability– pour up to one week

• Stock or custom trays

• Multiple casts

• Easy to mix

• Pleasant odor


Disadvantages• Expensive• Sulfur inhibits set

– latex gloves– ferric and Al sulfate

retraction solution

• Pumice teeth beforeimpressing

• Short working time• Lower tear strength• Possible hydrogen gas release

– bubbles on die– palladium added to absorb

Manikos Aust Dent J 1998

Addition Silicones

• Surfactants added– reduce contact angle– improved

• castability– gypsum

• wettability?? – still need dry field clinically

Pratten J Dent Res 1987 Mandikos Aust Dent J 1998

Elastic



Polysulfide

Silicones

Polyether

Condensation

Addition

Agar (reversible)



Polyether

• Indications– crown and bridge– bite registration

• Examples– Impregum F (3M/ESPE)– Permadyne (3M/ESPE)– Pentamix (3M/ESPE)– P2 (Heraeus Kulzer)– Polygel (Dentsply Caulk)

• Base– difunctional epimine-terminated prepolymer– fillers– plasticizers

• Catalyst– aromatic sulfonic acid ester– fillers

• Cationic polymerization– ring opening and chain extension

Composition


SO3-

+ R+

CH3 – CH – CH2 – CO2 – CH – (CH2)n – O – CH – (CH2)n – CO2 –CH2 – CH –CH3

N

H2C CH2

R R

m

N

H2C CH2

N

H2C CH2

R – N – CH2 – CH2 – +N

H2C CH2

N

H2C CH2

R – + +

Polyether Reaction

catalyst

base

ring opening


Manipulation

• Adhesive to tray– stock or custom tray

• very stiff

• Paste-paste mix• Auto-mixing

– hand-held• low viscosity

– mechanical dispenser• high viscosity

Advantages

• Highly accurate• Good dimensional stability• Stock or dual-arch trays• Good surface detail• Pour within one week

– kept dry

• Multiple casts• Good wettability


Disadvantages• Expensive

• Short working time

• Rigid– difficult to remove from undercuts

• Bitter taste

• Low tear strength

• Absorbs water– changes dimension


Impression Material Usage*Civilian General Dentists

• Crown & Bridge– vinylpolysiloxane 81%– alginate 38%– polyether 28%

• Inlays and Onlays– vinylpolysiloxane 71%– polyether 22%– alginate 20%

*Multiple responses DPR 2001

Impression Material Usage*Civilian General Dentists

• Complete dentures– alginate 58%– vinylpolysiloxane 55%– polyether 27%

• Partial dentures– alginate 78%– vinylpolysiloxane 43%– polyether 15%

*Multiple responses DPR 2002

Handling Properties

Agar Alginate PolysulfideCondensation

SiliconeAddition Silicone

Polyether

PreparationBoil,

temper, store

Powder, water

2 pastes2 pastes or paste/liquid

2 pastes 2 pastes

Ease of Use Technique sensitive

Good Fair Fair Excellent Good

Patient Reaction

Thermal Shock

Pleasant, clean

Unpleasant, stains

Pleasant, clean

PleasantUnpleasant

clean

Ease of removal

Very easy

Very easy

Easy Moderate ModerateModerate to difficult

Disinfection Poor Poor Fair Fair Excellent Fair


Handling Properties



Polyether

Working Time (min)

7 – 15 2.5 5 – 7 3 2 –4.5 2.5

Setting Time

(min)5 3.5 8 – 12 6 – 8 3 – 7 4.5

Stability 1 hour 100% RH

Immediate pour

1 hourImmediate

pour1 week

1 week kept dry

Wettability and

castabilityExcellent Excellent Fair Fair

Fair to good

Good

Cost Low Very low Low ModerateHigh to

very highVery high


Properties



Polyether

Elastic Recovery (%)

98.8 97.3 94.5 – 96.9 98.2 – 99.6 99 – 99.9 98.3 – 99.0

Flexibility (%) 11 12 8.5 – 20.0 3.5 – 7.8 1.3 – 5.6 1.9 – 3.3

Flow (%) -- -- 0.4 – 1.9 < 0.10 < 0.05 < 0.05

Shrinkage, 24 hours (%)

Extreme Extreme 0.4 – 0.5 0.2 – 1.0 0.01 – 0.2 0.2 – 0.3

Tear Strength (g/cm)

700380 – 700

2240 – 7410 2280 – 43701640 – 5260

1700 - 4800


Comparison of Properties

• Working time– longest to shortest

• agar > polysulfide > silicones > alginate = polyether

• Setting time– shortest to longest

• alginate < polyether < agar < silicones < polysulfide



• Stiffness– most to least

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

• Tear strength– greatest to least

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



• Cost– lowest to highest

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

• Dimensional stability– best to worst

• addition silicone > polyether > polysulfide > condensation silicone > hydrocolloid

Phillip’s 1996



• Wettability– best to worst

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

• Castability– best to worst

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


Regularly-Used Impression Materials*Civilian Practitioners

• Alginate 88%

• Polyvinyl Siloxane 85%

• Polyether 27%

• Other 6%

*Multiple Responses DPR 2005

Summary

• Study models– Alginate most widely used

• inexpensive

• displaces moisture

• lower detail reproduction

• dimensionally unstable

Summary

• Prosthodontics– Addition silicones most popular

• accurate

• dimensionally stable

• user friendly

• expensive

References• Phillips’ Science of Dental Materials, edited by K Anusavice,

11th ed., 2008, Saunders Publishing.

• Dental Materials and their Selection, edited by WJ O’Brien, 4th ed., 2008, Quintessence Publishing.

• Dental Products Report, 2001, 2002, 2005.

• CW Caswell, AS von Gonten, and TR Meng, Volumetric proportioning techniques for irreversible hydrocolloids: a comparative study, J Am Dent Assoc 1986 112:859-861.

• MN Mandikos, Polyvinyl Siloxane Impression Materials: An Update on Clinical Use, Australian Dental Journal, Dec 1998, 43(5): 428-434.

• RG Craig, Review of Impression Materials, Advance in Dental Research, Aug 1988, 2,51-64.

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