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withdrawn over undercuts :withdrawn over undercuts :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