Impression materials /certified fixed orthodontic courses by Indian dental academy

Impression MaterialsImpression Materials

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INDIAN DENTAL ACADEMY

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Impr

essi

on

Mat

eria

lsNon-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


Elastic



Polysulfide

Silicones

Polyether

Condensation

Addition

Agar (reversible)




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


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


Aqueous Hydrocolloids• Semi-permeable membranes

– poor dimensional stability• Evaporation• Syneresis

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

• Imbibition– water absorption

• swells



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 43 C

heat to 100 C



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 gelO’Brien Dental Materials & their Selection 1997


Advantages

• Dimensionally accurate• Hydrophilic

– displace moisture, blood, fluids• Inexpensive

– after initial equipment• No custom tray or adhesives• Pleasant• No mixing required



Disadvantages

• Initial expense– special equipment

• Material prepared in advanced• Tears easily• Dimensionally unstable

– immediate pour– single cast

• Difficult to disinfect



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



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 = OHS

-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



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 materialwww.indiandentalacademy.com

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



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)

Click here for DIS evaluations of VPS impression materialswww.indiandentalacademy.com

http://www.brooks.af.mil/dis/dm.htm#impress

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 before

impressing• 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


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



Handling Properties

Agar Alginate Polysulfide Condensation Silicone

Addition Silicone Polyether

PreparationBoil,

temper, store

Powder, water 2 pastes 2 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 Pleasant Unpleasant

clean

Ease of removal

Very easy

Very easy Easy Moderate Moderate Moderate

to difficult

Disinfection Poor Poor Fair Fair Excellent Fair



Handling Properties



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 hour Immediate

pour 1 week 1 week kept dry

Wettability and

castabilityExcellent Excellent Fair Fair Fair to

good Good

Cost Low Very low Low Moderate High to very high Very high



Properties



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) 700 380 –

700 2240 – 7410 2280 – 4370 1640 – 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



Comparison of Properties

• Stiffness– most to least

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

• Tear strength– greatest to least

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



Comparison of Properties• 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



Comparison of Properties• 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



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


• A good Impression must aid to fulfill M.M. Devan’s dictum: “It is the perpetual preservation of what already exists and not the meticulous replacement of what is missing.”


• DEFINITION• A COMPLETE DENTURE IMPRESSION is

the negative registration of the entire denture bearing, stabilizing and border seal areas, of either the maxillas or mandible in a plastic material that becomes relatively hard or set while in contact with these tissues.


A PRELIMINARY IMPRESSION is made for the purpose of diagnostic treatment planning and the construction of a custom tray while a FINAL IMPRESSION is used for making the master cast over which the denture bases are fabricated.


• According to GPT, 7th Edition, 1999 Impression is defined as a negative likeness or copy in reverse of the surface of an object; an imprint of the teeth and adjacent structures for use in dentistry


• The five objectives of an impression as stated by Carl.D. Boucher in 1944 are

• 1) PRESERVATION OF THE ALVEOLAR RIDGES. This is achieved by using impression techniques which cover maximum supporting areas as possible and using pressure within physiologic limit of the tissue.

• (2) RETENTION - The factors of retention are (1) adhesion (2) cohesion (3) interfacial surface tension (4) mechanical locking into undercuts (5) peripheral seal and atmospheric pressure and (6) oral and facial musculature. Henry A. Collet in 1965 stated that primary retention depends upon close adaptation to the tissues and is proportionate to the area covered.


• . (3) STABII.ITY - It is the relationship of the denture base to the underlying bone.

• Samuel Friedman in 1957, stated that stability is developed in the impression technique through more intimate contact of the labial and buccal flanges with the labial and buccal slopes and of the lingual flanges with the lingual slopes of the ridges. Boucher stated that stability requires maximum use of all bony foundations where the tissues are firmly and closely attached to bone.


• . (4) SUPPORT - Support is provided by the maxillary and the mandibular bones and their covering of mucosal tissue. It is enhanced by selective placement of pressures that are in harmony with the resiliency of the tissues that make up the basal seat.

• (5) ESTHETICS - Role of esthetics in impression making refers to the development of the labial and buccal borders, so that they are not only retentive but also support the lips and cheeks properly.


• Fisher R.D. in 1951 laid down six fundamental rules for making full denture impressions –

• (1) Roentgenographics, visual and digital examination of the oral cavity

• (2) Surgical removal of such abnormal formations as would prevent successful completion of impressions.

• (3) the require extension outlines. • (4) the location and position for area of

variable tissue displaceability (• 5) the required retention outline and • (6) the required adaptation.www.indiandentalacademy.com

• IMPRESSION TECHNIQUES may be classified depending on, [A] Amount of pressure used (Based on the theories of impression).

• Pressure technique based on pressure theory • Minimal pressure technique - based on

mucostatic theory.• Selective pressure technique -based on

selective pressure theory.


• [B] 1. Open or• 2. Closed mouth

• [C] 1. Hand-manipulation or• 2. Functional movements


• [D] Type of tray• 1. Stock tray : 1. Caulks Edentulous Rimlock

Trays.• 2. McGowen Winkler Trays (mandibular)• 3. STO-K Trays. (Square, round or Tapering

shapes of ridges).

• 2. Custom or special tray• 1. Shellac• 2. Acrylic• 3. Wax.



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Impression materials /certified fixed orthodontic courses by Indian dental academy