Impression Materials Final

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prosthodontics and dental materials

Text of Impression Materials Final


  • INTRODUCTIONImpression materials are used to register or reproduce the form & relationship of the teeth & oral tissues. They are used to make an accurate replica of the hard & soft oral tissues.

  • HISTORYBefore middle of the 18th century- Blocks of ivory & bone as IM.During 18th century Bees Wax, used in making impression1848 Colburn & Blake Gutta percha as IM.1844 Wescott, Dwinelle & Dunning Used Plaster of Paris as IM.1925 Alphous Poller 1st suggested use of agar for dental impressions

  • 1922 Everett Used Fluid wax of 3 consistenciesS.S. Wilding Patent to use algin for impressionMiddle 1950s Elastomeric impression materials introduced.1955 Pearsen New elastic impression material of polysulphide base.1960s Polyethers introduced in Germany.

  • IMPRESSION DEFINITION (WINKLER) :-Impression is defined as an imprint or negative likeness of the teeth of the edentulous areas where the teeth have been removed or of both, made in a plastic material that becomes relatively hard or sets while in contact with these tissues.

    IMPRESSION DEFN (GPT)A negative likeness or copy in reverse of the surface of an object; or an imprint of the teeth & adjacent for use in dentistry.

  • PRELIMINARY IMPRESSION (GPT)A negative likeness made for the purpose of diagnosis, treatment planning or the fabrication of tray.

    FINAL IMPRESSION (GPT)The impression that represents the completion of the registration of the surface or object.

    IMPRESSION MATERIAL (GPT)Any substance or combination of substances used for making an impression or negative reproduction.

  • PURPOSEConstructing a model or a cast is an important step in complete denture fabrication. Various types of casts & models can be made from gypsum products using on impression mold or negative likeness of a dental structure therefore the case must be an accurate representation of oral structures which requires that the impression be accurate.

  • IDEAL REQUIREMENTS:-Desirable flow properties.Set or harden at or near mouth temperature.Should not distort or tear.BiocompatableDimensionally stableCompatable with gypsum

  • 7.AccuracyPleasant odour, taste & esthetic colour.Adequate shelf life.Readily disinfectedNo release of gas during the setting of impression or gypsum products.Economic & easy to use

  • CLASSIFICATIONBased on setting mechanism.B.Based on mechanical propertiesBased on impression techniques

  • A. Based on setting mechanism.1.Thermoplastic (Reversible)(Ex.) Compound, AgarThermosetting (Irreversible)(Ex.) ZOE Paste, Alginate, Elastomers

  • Based on mechanical properties1. Elastic(Ex.) Elastomers, Hydrocolloids2. Inelastic (Ex.) ZOE Paste, Impression Compound

  • Based on impression techniques1.Mucostatic(Ex.) ZOE Paste, Impression Plaster2.Muco Compressive(Ex.) Hydrocolloids, Impression Compound

  • MATERIALS USED:-PlasterModelling CompoundZOE PasteHydrocolloidsElastomers

  • IMPRESSION PLASTER:COMPOSITIONb Calcium sulfate hemihydrateModifiersPotassium sulfatePigmentsRetardersGum tragacanthStarchFlavouring agentsAnti expansion solution

  • SETTING REACTIONThe setting reaction of gypsum occurs by dissolution of calcium sulfate hemihydrate, formation of a saturated solution of calcium sulfate, subsequent aggregation of less soluble calcium sulfate dihydrate and precipitation of the dihydrate crystals.ADVANTAGESGood Detail ReproductionEconomicalGood Dimensional StabilityNo distortion, it fractures before it can distort

  • DISADVANTAGESDisagreeable to the patientRigidity, critical areas may be lostRemoval of bulky impressionsRequires usage of separating media

    INDICATIONSWash impressionsRecording flabby tissues

  • IMPRESSION COMPOUNDCOMPOSITIONBeeswaxRosinCopal resinCarnauba waxPlasticizersTalcColouring agents

  • CLASSIFICATIONImpression Compound (Low Fusing)Tray Compound (High Fusing)

    LOW FUSINGIn the form cakes, sticks and conesColour varies from red, green, white, brown,Cakes used for preliminary impressions.Sticks and cones for border molding.

  • HIGH FUSINGIn the cake form, normally black in colour.Used as tray for wash impressions with impression plaster or zinc oxide eugenol.MANIPULATIONThe compound is softened by heating, either dry heat or in a hot water bath; water bath is preferred for complete dentures.The water bath temperature should be maintained between 60 & 65oC.Sticks & Cones can be softened by dry heat, but should be tempered before placing it in the patients mouth.,

  • ADVANTAGESCheapReusableNo irritationCan be re-modified and re-softened till accuracy is achieved.

  • DISADVANTAGESPoor surface reproductionPoor dimensional stability.Difficult to remove from under cuts.Unpleasant taste.Tempering required.

  • INDICATIONSPreliminary ImpressionsBorder Molding

  • ZINC OXIDE EUGENOL PASTE:COMPOSITIONBase Paste :Zinc Oxide87%Fixed Veg / Mineral Oil13%Accelerator Paste :Oil of cloves / eugenol12%Gum / polymerised rosin50%Filler20%Lanolin3%Resinous balsam10%Accelerator & colour5%

  • SETTING MECHANISMChelation Mechanism Chelate compound : Zinc eugenolate Final product : Unreacted zinc oxide particles with excess free eugenol in matrix of crystals of zinc eugenolate.

    DISADVANTAGESBurning sensationMessySticks to skin & instrumentsRigid

  • ADVANTAGESGood dimensional stabilityGood detail reproductionImpression can be modified by adding in deficient areasEasy to manipulateSufficiently long working time

    INDICATIONS :Secondary ImpressionsBite Registrations

  • IMPRESSION WAX - Waxes were first used in dentistry in the early 18th century for the purpose of recording impressions of edentulous mouths.

  • TYPES:- - Dental waxes are classified as: 1) Pattern wax 2) Processing wax 3) Impression wax - Impression wax is of 2 types: 1) Corrective wax 2) Bite registration wax

  • COMPOSITION:-- Waxes used in dentistry may be composed of natural & synthetic waxes, gums, fats, fatty acids, oils, natural & synthetic resins & pigments of various types.- Particular working characteristics of each of the dental waxes are achieved by the blending of appropriate natural & synthetic waxes & resins & other additives.

  • ALGINATES:-COMPOSITIONPotassium alginate-Soluble alginate- 15%Calcium sulfate-Reactor- 16%Zinc Oxide-Filler- 4%K titanium fluoride-Accelerator- 3%Diatomaceous earth-Filler- 60%Sodium phosphate -Retarder- 2%

  • SETTING MECHANISM :Sol-gel reaction, of soluble alginate with calcium sulfate & formation of an insoluble alginate gel.Calcium ions replace sodium or potassium ions of adjacent molecules to produce a cross linked complex or polymer network.

  • ADVANTAGESGood tear strengthBiocompatibleAdequate shelf lifeEconomic & easy to useDISADVANTAGESCannot record fine surface detailsDimensionally unstableIncompatibility with gypsumDistortion

  • AGARCOMPOSITIONAgar-Brush heap structure- 13-17% Borate-Strength- 0.2-0.5Sulfate-Gypsum hardener- 1-2%Wax-Filler- 0.5-1%Thixotropic materials Thickener- 0.3-0.5%Water-Reaction medium- Balance


  • SETTING MECHANISMSol-gel reaction

    ADVANTAGESMoist field OKAccurate and pleasantHydrophilicLow costLong shelf-life

  • DISADVANTAGESRequires special equipmentThermal discomfortTears easilyPour immediatelyDifficult to see margins and details

    INDICATIONS:Final impressionsDuplicating procedures

  • ELASTOMERSPOLYSULFIDESCOMPOSITIONBASE PASTE :Polysulfide polymer 80.85%Titanium dioxide, Zinc Sulfate 16.18 %Copper carbonate, silicaACCELERATOR PASTE :Lead dioxide 60.68 %Dibutyl phthalate 30.35 %Sulfur 3 %Other substances 2 %

  • SETTING REACTIONThe terminal & pendant mercaptan groups of the adjacent molecules are oxidised by the accelerator to produce chain extension & cross linking.

    ADVANTAGESLong Working TimeHigh tear resistanceModest cost

  • DISADVANTAGESRequires custom trayStretching leads to distortionStains clothingObnoxious odorPour within 1 hr.

  • CONDENSATION SILICONECOMPOSITIONBase Paste:Polydimethyl SiloxaneFillersAccelerator Paste:AcceleratorAlkyl SilicateSETTING REACTIONThe formation of elastomer occus through the cross linking of terminal groups of silicone polymers & the alkyl silicates to form a 3 dimensional network.Ethyl alcohol byproduct

  • ADVANTAGESPutty for custom trayClean and PlesantGood working time

    DISADVANTAGESHigh polymerization shrinkageVolatile by-productLow tear strengthHydrophobicPour immediately

  • ADDITION SILICONE (Polyvinyl Siloxanes)COMPOSITIONBase Paste:Polymethyl hydrogen siloxaneHybrid siliconeFillersCatalyst Paste:Divinyl polydimenthyl siloxanePlatinum salt activatorRetardersFillersSETTING REACTIONDoes not produce low molecular weight by product.Secondary reaction can occur with production of hydrogen gas if OH groups are present.

  • ADVANTAGESPutty for custom trayAutomix dispenseClean and pleasantIdeally elasticPour repeatedlyStable: delay pour

  • DISADVANTAGESHydrophobicLow tear strengthPutty displaces washPutty too stiffDifficult to pour castHigh cost

  • POLYTHERCOMPOSITIONBase Plate:Ethylene oxide & TetrahydrofuranFillerPlasticizerAccelerator Paste:Alkyl Aromatic SulfonateFillersPlasticizers

    SETTING MECHANISMThe elastomer is formed by c