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Impression materials and techniques

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  • IntroductionDefinitionHistoryIdeal RequirementsClassificationImpression materials - Elastomeric materials - Hydrocolloids Latest advances Impression Techniques

  • Introduction

  • Impression materials are used to produce the accurate replicas of intraoral tissues.

    There are a wide variety of impression materials available each with their own properties, advantages and disadvantages.

    Materials in common use can be classified as elastic or non-elastic according to the ability of the set material to be withdrawn over undercuts.

  • Definition

  • Any substance or combination of substances used for making an impression or negative reproduction. - GPT

  • An impression is an imprint or negative likeness of the teeth and/or edentulous areas, made in plastic material which becomes hardened or set while in contact with the tissue. -Hartwell 1992

  • An impression is the perpetual preservation of what already exists and not the meticulous replacement of what is missing. -M.M.Devan 1995

  • 1782 : William Rae used wax with Plaster of Paris.1940s: American dentists used Plaster OF Paris for impression & the technique was presented to the profession at large by Chaplin Harris in 1953.1925 : Alphous Poller of Vienna was granted a British Patent for a totally different type of impression material which was later described by Skinner as Colloidal Sols of Emulsoid type. The possibility of using colloidal substance for dental impression became apparent when Pollers Negacoll was modified & introduced into the dental profession as Dentacol in 1928. Agar hydrocolloid was introduced to the dental impression.1930 : JD Hart of Oklahoma began to use Agar for fabrication of cast restoration.

  • 1930 : AW Ward and EB Kelly introduced ZnO Eugenol.1890s : A chemist from Scotland noticed that Brown Seaweed yielded peculiar mucous extraction. He named it Algin.1936-40 : S William Wilding used Algin as a dental impression material1950s : Development of Rubber base impression materials (Polysulphides and Condensation Silicones)1960s : Polyether impression material developed in Germany1970s : Addition silicone was introduced as a dental impression material1988 : Latest addition and light cure elastomers1990-2000 : New auto devices and delivery systems

  • Ideal Requirements

  • Fluid enough to adapt to the oral tissuesViscous enough to be contained in the traySetting time - less than 7 minutesAdequate tear resistanceDimensionally stableBiocompatible Cost effective

  • Classification

  • I. Based on the degree of tissue compression/ amount of pressure applied

    Mucostatic Ex: Impression plaster Mucocompressive Ex: Impression Compound

  • II. Based on Mode Of Setting & Elasticity

    A. Chemical reaction (irreversible)By elasticity and use Inelastic or rigid Elastic Materials Use Material Use 1.Plaster of Paris 2.Zinc-oxide eugenol Edentulous ridge Interocclusal records 1. Alginate 2. Non-aqueous elastomers Polysulfide Polyether Condensation silicone - Addition silicone Teeth and soft tissue B. Physical reaction (reversible)3.ImpressionCompoundPreliminary impression 3.Agar hydrocolloid Teeth and soft tissue

  • III. Based on the chemical composition

  • IV. Based on type of impression & area of use

  • V. According to the use of the materials in dentistry

    A) Materials used for obtaining impression of dentulous mouth

    AlginateAgarNon-aqueous Elastomers

    B) Materials used for obtaining Impression of edentulous mouth:

    Impression Compound Impression Plaster Zinc Oxide eugenol Wax

  • VI. Based on Manipulation

  • VII According to their method of use

  • VIII. Based on the tray used for impression

  • Hydrocolloids

  • Colloids often classed as fourth state of matter as colloidal state. can be considered as a compromise between the very small molecules in solution & very large particles in suspension. Two phases Dispersed phase or dispersed particles Dispersion phase or dispersion medium All colloidal dispersions are termed as sols.

  • Types Of ColloidsThe only exception is the gaseous state, i.e. two gases.

  • Hydrocolloids If the dispersion medium is water, the material is known as hydrocolloid. Particles larger than those in solution. Particle size ranges from 1-200 nm. There is no clear line of demarcation among the solutions, colloids & suspensions.

    Gels Colloids with a liquid as a dispersion medium can exist in two different forms known as Sol & Gel.

  • Sol- has a appearance & many characteristics of a viscous liquid. Gel- is a semisolid & produced from a sol by the process of gelation.

    GelationIt is a process of conversion of sol to gel, to form fibrils, micelles of the dispersed phase which become interlocked to give characteristic jelly like consistency.

    Within the gel, the fibrils branch & intermesh to give a brush heap structure.

  • micellesbrush-heap structure

  • Gelation Temperature The temperature at which gelation occurs is known as gelation temperature. Agar - secondary bonds (weak) hold the fibrils together- break at slightly elevated temperatures and become re-established as it cools to room temperature - reversible

    Alginate - the fibrils are formed by chemical action - irreversible

  • The Gel may lose water by evaporation from its surface or by exuding fluid onto the surface by a process known as SYNERESIS. The gel shrinks as a result of evaporation & syneresis.

    If a gel is placed in water, it absorbs water by a process known as IMBIBITION. The gel swells during imbibition, thereby altering the original dimensions.

    The effects of syneresis, evaporation & imbibition on the dimensional changes are of considerable importance in dentistry, since any change in dimension that occurs after the impressions are removed from the mouth will lead to inaccurate casts & models.


  • Reversible hydrocolloids undergo transition from gel to sol on heating.

    On cooling they return back to the original state.

    The hydrocolloid supplied as the gel is heated above its liquefaction temperature, cooled to a temperature compatible with the oral tissues & placed in the mouth. Gelation occurs as the tray continues to cool, after which the impression is removed & poured.

  • Agar It is a sulphuric ester of a linear polymer of galactose. Gelation Temperature of agar is approx- 37-50c. The temperature at which the gel changes to sol i.e. liquefaction temperature is 70-100c.

    Although it is an excellent impression material & yields accurate impressions, it has been largely replaced by alginates & rubber impressions because- Of the minimum equipment required Possibility of obtaining metal dies from rubber impression.

  • ComponentFunctionComposition AgarBrush heap structure13 17% BoratesStrength0.2 0.5% SulfatesGypsum hardener1.0 2.0% WaxFiller0.5 1.0%Thixotropic materialsThickener0.3 0.5% WaterReaction mediumBalance 84%Alkyl BenzoatesPreservatives0.1% Color and FlavorsTaste & appearanceTrace

  • Mode of supply :Gel in collapsible tubes (for impressions)A number of cylinders in a glass jar (syringe material)In bulk containers (for duplication)

  • Full mouth impressions without deep undercutsQuadrant impressions without deep undercutsSingle impressionsCan be used for crown and bridge impressions because of their accuracyCast duplicationTissue conditioner

  • ManipulationPreparation, conditioning and tempering of the agar material:

    Before use the material is subjected to a controlled regimen in three water baths.

    Liquefying bath -100C for 10 min.Storage bath 63-66C Tempering bath- 44-46C for 3-10 min.

  • Conditioning unit

  • Making the Agar impression

  • Syringe material, directly taken from storage compartment - applied on to the prepared tooth.Water-soaked outer layer of tray hydrocolloid is removed from the tempering basin, outer layer removed and impression made. Gelation is accelerated by circulating cool water (18-21oC) through the tray for 3-5 min.

  • According to ADA specification no.11 :-Compressive strength : 8000 gm/cm2Tear strength : 700 gm/cm2Viscosity : Sufficient fluid to allow detailed reproduction of hard and soft tissuesFlexibility: 11% when a stress of 14.2 psi appliedElastic recovery : 98.8%Accuracy : 25mWorking time : 7-15 min.Setting time : 5 min.Gelation temperature : 37-50CLiquefaction temperature : 70-100C

  • HydrophilicGood elastic propertiesCan be re-used as a duplicating materialLong working time and low material costNo mixing technique, the potential for errors are eliminatedPalatable and well tolerated by patientsHigh accuracy and fine detail recordingCompatible with die and cast materials

  • Low tear resistanceLow dimensional stabilityOnly one model can be usedExtensive and expensive equipment requiredIt can not be elecroplatedImpossible to sterilize for re-use


  • Developed as a substitute for the agar impression material when its supply became scarce during World War II.Based on a natural substance extracted from certain brown seaweed. This substance is called as-anhydro--d-mannuronic acid or alginic acid (sodium or potassium or triethanolamine acid) (insoluble in water)

  • Currently, alginate is more popular than agar because- easy to manipulate comfortable for the patient. relatively inexpensive does not require elaborate equipment

  • Composition

    ComponentFunctionWeight percentage Potassium alginateSoluble alginate15 Calcium sulfateReactor16Potassium titanium FluorideAccelerator3 Zinc oxideFiller particles4 Diatomaceous earthFiller particles60 Sodium phosphateRetarder2


    Two main reactions occurs during setting :

    2Na3PO4 + 3 Ca SO4 Ca3(PO4)2 + 3 Na2SO4(Sodium phosphate) (Calcium sulphate) (Retarder) (Reactor)

    Sodium Alginate + CaSO4 + H2O Ca Alginate + Na2SO4 (Powder) (Reactor) (Gel)

  • I. According to concentration of sodium phosphate Fast set Regular set II. According to concentration of filler Soft set Hard set Classification of alginate (Robert G. Craig)

  • Types Mixing time Working time Setting timeI- Fast set 45 sec 1.25 mins 1-2 minsII- Normal set 60 sec 2 mins 2-4.5 minsMANIPULATION :-Prepare a proper mixture of water & powder.The measured powder is sifted into the premeasured water.Water added first to ensure complete wetting of powder particles.Clean equipment is important.Avoid incorporating air into the mix.Figure of-eight motion is best, with the mix being swiped or stropped against the sides of the bowl with intermittent rotations (180) of the spatula to press out air bubbles. All of the powder must be dissolved.

  • PROPERTIES :-According to ADA specification No 18:Flexibility : 14% at a stress of 1000gm/cm2Elastic recovery : 97.3%Tissue detail reproduction : 0.075mmCompressive strength : 5000-8000/cm2Tear strength : 350-700gm/cm2Poor dimensional stability

    USES :-Impression making in complete denture prosthesis and orthodonticsIn undercuts and in excessive salivary flowFor impressions for mouth protectorsFor impression in study models and working cast.

  • ADVANTAGES :-Easy to mix and manipulateMinimum requirement of equipmentFlexibility of set impressionAccuracy if properly handledLow costHygienic, fresh material for each impressionGood surface details even in salivaComfortable to the patient

    DISADVANTAGES :-Cannot be electroplatedDistortion occurs easilyPoor dimensional stabilityPoor tear strength

  • RECENT ADVANCES IN ALGINATESSol containing water but no source of calcium ions .A reactor of Plaster of Paris can be added to the sol later.The two component system may be in the form of two pastes- One contains the alginate sol and the other contains the calcium reactorSiliconised alginatesChromatic alginates eg. Integra & KromaFaze (Dux dental) ,Take one alginate(Kerr)Dustless alginates( glycerin is added on the alginate powder to agglomerate the particles) eg.Identic dust free alginate (Dux dental),Jeltrate Dustless(Dentsply Caulk) , Integra dustfree alginate(Kerr)AlginotAlginator 2

  • Laminate technique (Alginate Agar Method)The hydrocolloid in the tray is replaced with a mix of chilled alginate that bonds to the syringe agar. Alginate gels by a chemical reaction whereas agar gels by means of contact with the cool alginate rather than with the water circulating in the tray.Since the agar, not the alginate is in contact with the prepared tooth, maximum detail is produced.

  • ADVANTAGES :-Most cost effective way of producing an impression with adequate detail. less preparation time required.

    DISADVANTAGES :-The bond between the agar & alginate is not always sound.The higher viscosity of the alginate material displaces the agar hydrocolloid during seating.Dimensional inaccuracy of the alginate hydrocolloid limits its use to single units.

  • Elastomeric Impression Materials

  • Soft and rubber-like & known as elastomers or synthetic rubbersAs per ADA Sp. No.19- non-aqueous elastomeric dental impression materialsLiquid polymers when mixed with a suitable catalyst are converted into solid rubber at room temperature.TYPES :-I. According to chemistry PolysulphidesCondensation polymerizing siliconeAddition polymerizing siliconePolyetherVisible light curable polyether urethane dimethacrylate ( a new class added recently)

  • II.ADA ClassificationBased on selected elastic properties & dimensional changes(sp no.19) Maximum permanent Maximum flow Maximum dimensional deformation in compression change in 24 hrsType I 2.5 0.5 -0.5Type II 2.5 0.5 -1Type III 5.5 2.0 -0.5Each type is further divided into four viscosity classes;III. According to Viscosity(ISO 4823) 1) Light body or syringe consistency 2) Medium or regular body 3) Heavy body or tray consistency 4) Very heavy body or putty consistency

  • Excellent reproduction of detailsGenerally hydrophobicGood elastic propertiesExcellent tear strengthHigh coefficient of thermal expansionElectroplatable :-silver or copper platedExtended shelf-life : 2 yearsGenerally higher costRequires tray adhesive and mechanical interlocking.

  • Dimensional changes occur due to :- - Curing shrinkage - Loss of by products of reaction - Condensation silicone lose alcohol - Polysulphide lose volatile accelerators(Hydroperoxide type) - Polyethers absorb water and loses soluble plasticizers - Thermal contraction when transferred from mouth to room temperature. - Incomplete elastic recovery after removal - Increased filler content reduces the shrinkage - Uniform thickness of the material : shrinkage more uniform - Good adhesion of tray : Shrinkage is directed towards outer surface of the tray - Time of pouring : after elastic recovery

  • SUPPLIED AS :-All elastomers two paste systems(base and catalyst)Putty consistency supplied in jarsUSES :-1) Impression material for all applications including - Fixed partial dentures - Dentulous and edentulous impressions2) Border moulding of special trays(polyether)3) Bite registration4) As duplicating material for refractory casts

  • Polysulfide (Synonyms : Rubber base, Mercaptan, Thiokol rubber)

  • First elastomeric impression to be introducedComposition : Base paste : Liquid Polysulphide Polymer - 80-85% Inert fillers( Titanium dioxide, Zinc sulfate , - 16-18% copper carbonate or silica) Plasticizers Reactor Paste Lead dioxide - 60-68% Dibutyl phthalate - 30-35% Sulfur - 3% Other substances like Magnesium Stearate(retarder) & deodorants - 2%

  • Tray adhesive :- Butyl rubber or styrene/acrylonitrile dissolved in a volatile solvent such as chloroform or a ketone is used with polysulphides

    Mode of supply: - Available as 2 systems : Base and accelerator - 3 viscosities: light, medium and heavy bodiesChemistry and Setting Reactions :-

    On mixing base and accelerator pastes the liquid polymer sets to form a solid, but flexible and elastic rubber like material.

  • Lead dioxide reacts with the polysulfide polymerChain lengthening by oxidation of the terminal SH groupsCross-linking by oxidation of the pendant SH groups PbO2 + SHS - R - SH HS - R-S-S-R-SH + H2OOR

    Mercaptan+ Lead dioxide Polysulphide + WaterCommercial products :

    Permlastic (Lead dioxide system), Coeflex, Omniflex (Copper hydroxide system)

  • AdvantagesDisadvantages - High tear strength - Dimensionally unstable

    - Long working time- Unacceptable odor - Established precision- Untidy and stains clothing - Economic- Long setting time

    - Extensive shelf life- Least elastic recovery - Less hydrophobic- Subsequent pours are less accurate.

  • Silicones

  • These materials were developed to overcome some of the disadvantages of polysulphide materials :-Objectionable odorStaining of linen by lead dioxideAmount of effort required to mix the base with the acceleratorLong setting timesModerately high shrinkage on settingFairly high permanent deformationPouring should be within one hourTYPES :- - Condensation silicone - Addition silicones

  • Polymer chains grow simultaneously and a reaction byproduct is formed with associated shrinkageProducts available:- - Accoe(GC) - Cuttersil(Heraeus Kulzer) - Silene(Bosworth) - Speedex(Coltene Whaledent) - Xantopren(Heraeus Kulzer)Advantages :- -It is clean and pleasant - Good working time - Easily seen marginsCONDENSATION SILICONE

  • DISADVANTAGES :- - High polymerization shrinkage - Volatile alcohol byproduct - Low tear strength - Hydrophobic - Pour immediatelyCOMPOSITION :- Base Paste - Polydimethylsiloxane (Hydroxy-terminated) - Colloidal silica or microsized metal oxide(filler) 35-75% - Colour pigments Accelerator Paste - Orthoethyl silicate - (cross linking agent) - Stannous octoate - catalyst


  • These reactions are effected at ambient temperatures and the materials are therefore called RTV( Room Temperature Vulcanization) silicones.

    The ethyl alcohol formed evaporates gradually leading to shrinkage & instability. So a condensation silicone should be poured as soon as possible after removal from the mouth.

  • Also called as polyvinyl siloxanesHas better properties than condensation siliconesMODE OF SUPPLY :-Available in various viscosities and paste and jars with contrasting colorsEg: - Impressiv( Cosmedent) - Imprint 3 Penta (Putty impression material with automix) - Aquasil/Reprosil/Hydrosil(Dentsply Caulk) - Exaflex/ Examix/Exafast/Hydroflex(GC America) - Express, Imprint/Imprint II(3M ESPE) - Flexitime(Heraeus Kulzer)ADDITION SILICONE

  • Composition:- Base :- - Poly(methyl hydrogen siloxane) - Other siloxane prepolymers - Fillers Accelerator : - Divinyl polysiloxane - Other siloxane prepolymers - Platinum salt : Catalyst (chloroplatinic acid) -Palladium (Hydrogen absorber) - Retarders - Fillers

  • CHEMISTRY AND SETTING REACTION :-Vinyl siloxane + Silane siloxane Silicone rubber

  • Complications from latex gloves :-

    Contact of polyvinyl siloxanes with latex gloves should be avoidedEspecially true when handling and placing gingival cordsMechanism :- - Migration of particulate sulfur and sulphur chloride compounds to the surface and are transferred to prepared teeth and adjacent soft tissues - When mixing by hand, mechanism of inhibition is thought to be contamination of chlorplatinic acid catalyst with free sulfur left in glove - Residues from acrylics,methacrylates and petroleum jelly lubricants may interfere with setting reaction of materialContact of internal surface of impression with gloved hands :- - Failure of the material adjacent to the tray to polymerize - Separation of the tray from the impression material

  • Prevention :- - Use vinyl or nitrile gloves to eliminate the problem - Preparations should be cleaned after temporary prosthesis before making final impression - Avoid handling retraction cords with latex gloves

    TRAY ADHESIVE :-Polydimethyl siloxane & Ethyl silicate

  • Available in 4 consistencies Light bodyMedium body Heavy body Putty

  • AdvantagesDisadvantages - Excellent dimensional accuracy - Hydrophobic - Long term dimensional stability- Expensive - Hydrogen gas evaluation in some materials - Pleasant to use- Short setting time- Hydrophilic formulations imbibe moisture- Auto mix available- If hydrophilic, good compatibility with gypsum - Sulfur contamination by latex glove

  • PolyetherIntroduced in Germany in late 1960s Good mechanical properties and dimensional stability, but short working time, very stiff material and expensiveCommercial names: - Impregnum(ESPE,Germany) - Permadyne(ESPE,Germany)Available as 3 viscosities: light,medium & heavy bodied

  • COMPOSITION :- Base Paste - Polyether polymer - Colloidal silica(filler) - Glcol ether or phthalate(plasticizer) Accelerator paste - Aromatic sulfonate ester (cross-linking agent) - Colloidal silica (filler) - Phthalate or glycol ether (plasticizer)CHEMISTRY & SETTING REACTIONPolyether + Sulfonic ester Crosslinked rubber

  • PROPERTIES :- - fast setting time of less than five minutes -Undergo addition based polymerization reaction - Have no reaction by product so are dimensionally stable - Must be stored dry as they absorb water and swell under conditions of high humidity - Are relatively hydrophilic and hence more forgiving of inadequate moisture control - Have good tear resistance, but are rigid, hence considerable force may be required when removing from mouth or cast

  • AdvantagesDisadvantages Dimensional stability- Set material very stiff Accuracy- Imbibition Shorter setting time- Short working time. Automix available- Allergic hypersensitivity in some cases.

  • PROPERTIES OF ELASTOMERIC IMPRESSION MATERIALSAccuracy :- - According to ADA sp no 19, elastomeric impression materials must be able to reproduce fine detail of 25m. Differences in ability to record fine detail of various viscosities :- -Lower the viscosity of impression materials , better it will record fine detailsElastic recovery :- -No impression material has 100% elastic recovery - Eliminate or block out any undercuts in the tooth preparation before making impressionDimensional stability - PVS materials possess ideal dimensional stability - Hydrocolloids are subject to imbibation & syneresis

  • Flow & flexibility - Addition silicone and polyether are pseudoplastic impression materialsRigidity - Polyether impression materials tend to be more rigid than the other materials - PVS materials are reasonably stiff, but fracture of the dies are uncommon - Reversible hydrocolloid is the least rigid of all impression materials -With dual arch impressions, use a very rigid impression material.Workability - Automix devices, electronic mixing devices, and simpler mixing guns provide a standardized mix

  • Hydrophilicity :- - Reversible hydrocolloid impression materials are truly hydrophilic - Polyether impression materials are also hydrophilic but require a dry field for making impressions - The original PVS were hydrophobic but wettability is improved in the later formulationsShelf life :- -No more than 6 months supply of impression material should be kept on hand at any timePatient comfort :- - Polysulphide & Agar is less patient friendlyEconomic factors :- - Reversible hydrocolloid is less expensive than elastomeric impression materials

  • RECENT ADVANCESVisible light cured polyether urethane dimethacrylateIn early 1988, a visible light cured impression was introduced(Genesis L.D. caulk).Two viscosities :-Light and heavy bodiedComposition :- - Polyether urethane dimethacrylate - Photoinitiators (camphoroquinone) - Photoaccelerators (Diethyl amino ethyl methacrylate) - Silicone dioxide (Filler)Chemistry :- Similar to light cured composites

  • Properties :- - Long working time and short setting time - Blue light is used for curing with transparent impression trays - Tear strength-6000-7500 gm/cm2 (Highest among elastomers) - Dimensional stability, flow, detail reproduction, permanent deformation, wettability, compatibility with cast and die materials and electroforming is similar to addition silicone

  • Manipulation :- - Light body is syringed into the sulcus and over the preparation -Heavy body is loaded onto a clear tray and seated over the light body - Both are simultaneously cured with a visible light curing unit having an 8mm or larger diameter probe - Curing time is approximately 3 mins

  • Advantages :- - Controlled working time - Excellent properties Disadvantages :- - Need special transparent trays - Difficult to cure in remote area

  • Automatic dispensing and mixing devices-This latest technique consists of a double barrel caulking gun with mixing tip. The tip contains spirals on the inside. Forcing of the base & accelerator results in its mixing.e.g. Volume mixer (Kerr), Pentamix(3M ESPE)

  • Advantages :-More uniform mixLess air bubblesReduced working time

  • Senn (GC America) :-Hybrid polyether/polysiloxane material that has both hydrophilicity and dimensional accuracy, before, during and after set.

  • MATERIALADVANTAGESDISADVANTAGESALGINATERapid set, HydrophilicLow cost, No custom tray requiredPoor accuracy & surface details, Low tear rsistanceLow stability.AGAR-AGARLong working timeHydrophilicLow tear rsistanceLow stabilityEquipment requiredPOLYSULFIDEHigh tear resistanceLong setting timeUnpleasant odor, StickyADDITION SILICONEDimensional stability, excellent accuracy, Auto mix availableHydrophobic, release of hydrogen gas, Most expensiveCONDENSATION SILICONEFair accuracy, short setting timeRelease of Alcohol byproduct, Hydrophobic.POLYETHERDimensionally stable, accurate, Auto mix availableRigid, imbibitionshort working time,


    MaterialMethodRecommended disinfectantCommentsIrreversible hydrocolloid (alginate)Less than ten min. immersion with cautionChlorine compounds or iodophorsShort term glutaraldehyde also has to be acceptable.Reversible hydrocolloidDo not immerse in alkaline glutaraldehydePolysulfideImmersionGlutaraldehydes, chlorine compounds, iodophors, phenolicsDisinfectants requiring more than 30 min exposure times are not recommended

  • MaterialMethodRecommended disinfectantCommentsPolyether Immerse with caution. Use only disinfectant with a short exposure time (

  • ClassificationBased on the position of the mouthOpen mouth techniqueClosed mouth technique (functional impression )

    Based on the pressure applied Positive pressureNegative pressureSelective pressure technique

  • Based on the mixing techniqueDouble mix Heavy-light body technique Putty wash techniqueOne stage simultaneousTwo stage relief channel - 2mm spacer techniqueSingle mix or monophase technique

    According to the tray used Custom tray impressions Stock tray impressions

  • Three most common methods for making impressions for fixed restorations are-

    Simultaneous dual-viscosity technique,

    Single-viscosity or monophase technique, Putty-wash technique

  • Simultaneous dual-viscosity technique

    low-consistency material is injected with a syringe into critical areas & the high-consistency material is mixed & placed in an impression tray.

    After injecting the low viscosity material, the tray containing the higher viscosity material is placed in the mouth.

    Since both the materials are mixed together, they join, bond & set together.

    After the materials have set, the tray & the impression are removed.

  • Advantages Over comes the polymerization shrinkage of the light body materialMargins duplicated in light body

    Disadvantages Use of custom tray An assistant required for mixing the material - tray/syringe simultaneously Margins duplicated in heavy body in case of excess pressure

  • Single viscosity or monophase technique

    Impressions often made with a medium viscosity impression material.

    Addition silicone & polyether are well suited for this technique because both have a capacity for shear thinning.

    When the medium viscosity material is forced through an impression syringe, viscosity is reduced, whereas the viscosity of the same material residing in the tray is unaffected. This behavior of the materials is referred to as PSEUDOPLASTIC.

  • Advantages Reduced wastage of the material Less time consumption Avoids the time involved in fabrication of custom tray

    Disadvantages Relatively high viscosity and reduced flow of the monophase materials, makes their injection onto the preparation more difficult to control -increased incidence of surface voids - Stephen M. Dunne et al 1998


  • Two steps impression procedure whereby a preliminary impression is taken in high or putty consistency material before the tooth preparation is made.

    Space is provided for a low consistency material by a variety of techniques, & after tooth preparation, a low consistency material is syringed in to the area & the preliminary impression reinserted.

    The low & high consistency materials bond, & after the low consistency material sets, the impression is removed. This procedure is sometimes called a WASH TECHNIQUE.

    The Putty consistency materials & this technique were developed for condensation silicones to minimize the effects of dimensional change during polymerization. This technique was extended to addition silicones after their introduction even though their polymerization shrinkage is significantly lower.

  • Putty wash simultaneously technique (One stage)

    Light body material syringed on to the preparation while the putty material loaded in a stock tray is simultaneously inserted into the mouth.

  • Advantages Reduced chair side time

    Disadvantages Absolute lack of control in the bulk of wash materialBy mixing putty, syringe material simultaneously, setting distortion of putty included in over all distortion of impression - Chee and Donovan 1992Possibility of margins duplicated in putty mediumTendency of bubbles to be formed and occluded in the set impression

  • Putty wash relief channel technique

    Pre-operative putty impression is made intra orally

    In the area where the tooth is to be prepared, impression material is removed or channels prepared using putty cutter instrument

    The impression is then relined with low viscosity material

  • Advantages Impression can be captured with the wash materials

    Disadvantages To confine the wash material to area of relieved impressionIf entire area is washed - creates hydraulic displacement of putty impression resulting in smaller dies - Donovan TE 2004

  • Putty wash 2mm spacer technique

    2 mm thick wax spacer is prepared on a diagnostic cast, occlusal stops are provided on non-functional cusps.

    A putty impression is made with a stock tray resulting in a putty custom tray with 2mm space for the wash material.

    Putty custom tray is then washed with light body material.

  • Advantages Wash stage carried out after the putty has set and contracted Controlled wash bulk compensates for this contraction with minimal dimensional changeDisadvantages Extra chair side time Extra material

  • Clinicians have an excellent array of impression materials & techniques for fabrication of tooth restorations.

    Based on the quality of impressions sent to the commercial laboratories, it seems that many impressions fall short of the quality made possible by current impression materials.

    Thus it is important to review the contemporary principles of impression materials & to take impressions consistent with those principles. It is thus important to familiarize with the various specialty impression techniques available & use them when indicated.

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