IMPRESSION IMPRESSION MATERIALSMATERIALS

DR ZURYATI AB GHANIDR ZURYATI AB GHANI

BDS (WALES), Grad Dip BDS (WALES), Grad Dip ClinClin Dent (Adelaide), Dent (Adelaide), Doctor in Clinical Dentistry (Doctor in Clinical Dentistry (prosthodonticsprosthodontics), ),

Adelaide, FRACDS (Australia).Adelaide, FRACDS (Australia).

18.06.0718.06.07

Impression materialsImpression materials

PlasterCompoundZOE pasteWax

Non AqueousPolysulphideCondensation SiliconeAdditional SiliconePolyether

Non Elastomeric Elastomers

AqueousReversible hydrocolloid (Agar)Irreversible hydrocolloid(Alginate)

DESIRABLE PROPERTIESEasy to mix and dispenseDimensionally stableGood wettingAccuracy in detailAccuracy after cold sterilisationOdor and taste neutralGood elastic recoveryGood tear strengthCompatibility with die materialsLong shelf lifeAdequate working timeNo irritation to tissues

KEY LEARNING ISSUESClassification of materialsUnderstanding setting reactionPropertiesDelivery systemsProblems and their solutions

Non Non elastomericelastomericimpression materialsimpression materials

CompoundCompound

CompoundCompound

Composition: 40%resin, 7% waxes, Composition: 40%resin, 7% waxes, 3% organic acids, 50% fillers, 3% organic acids, 50% fillers, colouringcolouring agentsagentsCapable of Capable of mouldingmoulding impression at impression at 4545°°CCPrimary impression in the edentulous Primary impression in the edentulous ridgeridge

Zinc oxide Zinc oxide EugenolEugenol

Composition

Tube 1Tube 1Zinc oxide Zinc oxide OilsOilsAdditives

Tube 2Tube 2EugenolEugenolOilOilResinResinAdditives

AdditivesAdditives

Zinc oxide Zinc oxide eugenoleugenol

Used in custom made tray to record Used in custom made tray to record usually edentulous arches, sometimes usually edentulous arches, sometimes referred as wash impressionreferred as wash impressionMixing time 30 to 45 Mixing time 30 to 45 secssecsSetting time 3 to 5 Setting time 3 to 5 minsminsBrittle, messy, sometimes irritates Brittle, messy, sometimes irritates patient due to patient due to eugenoleugenol contentcontent

Zinc oxide Zinc oxide eugenoleugenol

Impression waxesImpression waxes

Useful for correction of small Useful for correction of small imperfection in imperfection in ZnOEZnOE impression, or impression, or for recording partial lower free end for recording partial lower free end saddlessaddles

Aqueous Aqueous elastomericelastomericimpression materialsimpression materials1)1) AgarAgar-- Reversible hydrocolloidReversible hydrocolloid2)2) Alginate Alginate ––irreversible hydrocolloidirreversible hydrocolloid

AlginateAlginate

One of the most widely used One of the most widely used impression materialsimpression materialsADVANTAGES: Easy to mix and ADVANTAGES: Easy to mix and manipulate, cheap, flexibility of set manipulate, cheap, flexibility of set impression, minimum equipment, impression, minimum equipment, accuracy if handled properly.accuracy if handled properly.

ALGINATEALGINATEComposition FunctionSodium or potassium Sodium or potassium alginatealginateSodium phosphateSodium phosphateSilicate powderSilicate powderPotassium Potassium sulphatesulphate or or potassium zinc fluoridepotassium zinc fluoride

Organic glycolOrganic glycol

Chlorhexidine

To dissolve in waterTo dissolve in water

To react with alginateTo react with alginateControl setting timeControl setting timeTo aid setting of die To aid setting of die materialmaterial

Min dust during Min dust during dispensingdispensingSelf disinfectionChlorhexidine Self disinfection

Mixing time: 1 minMixing time: 1 minSetting time: 2Setting time: 2--4.5 4.5 minsminsFast set: 1Fast set: 1--2 2 minsmins↑↑Temp Temp ↑↑setting time. Do not alter powder setting time. Do not alter powder liquid ratio to change setting timeliquid ratio to change setting time

Dimensional changes. Can be stored Dimensional changes. Can be stored at 100 % humidity for 1 hr without at 100 % humidity for 1 hr without dimensional changesdimensional changesNot very accurateNot very accurateLow tear resistanceLow tear resistance

Non-Aqueous Elastomers

PolysulfidesCondensation SiliconesAddition Curing SiliconesPolyethers

Also known as thiokol rubbers or mercaptansProvided as two pastes: Base and Catalyst

CompositionBase:Polysulfide polymer Titanium oxide or Zinc Oxide Calcium Sulfate

Catalyst:Lead dioxide Sulfur Dibutyl phthalate

Products: Permlastic (Kerr); Omniflex (GC-America)

SETTING REACTIONCondensation reaction between –SH (sulfydryl groups)with lead dioxide and sulfur to produce disulfide linksand water.Chain lengthening and cross-linking occursIncrease in viscosityElastic properties ariseWater accelerates the setting reactionHeat accelerates the setting reaction

O from Pb2O

Sulfydryl group

ADVANTAGESGood tear strength and flexibilityLow costIncreased working time

DISADVANTAGESPoor dimensional stability due to water lossOffensive odorLong setting timeMore permanent deformation on removal andless elastic recovery due to reduced degree ofpolymerisation compared to silicones and polyethers

DIMENSIONAL CHANGE FROM:Temperature transition upon removal from mouthWater loss which is a setting reaction by-productShrinkage from continued polymerisation

Initial mix on pad

Final mix ready for dispensing

COMPOSITIONBase:Dimethyl polysiloxaneAlkyl silicate

Catalyst:Stannous octoate

Setting reaction:Cross-linking of a hydroxy terminated dimethyl polysiloxaneby an alkyl silicate catalysed by stannous octoate

Dimethyl polysiloxane

Tetra ethyl orthosilicate

ADVANTAGESMore stable than polysulfidesGood tear strengthGood working and setting times

DISADVANTAGESOdor from alcohol byproductDimensional instability

Most accurate impressions with condensation silicones aregenerated via a putty-wash technique.

Products: Formasil, Accoe (GC America)

Poly-Vinyl Siloxanes

Setting reaction can be inhibited via a sulfur compound insome latex gloves by the name of zinc diethyl dithiocarbamateThis chemical interacts with the chloroplatinic acid catalyst inthe PVS formulationNot all latex gloves cause problems for PVS materials

PolyVinyl Siloxanes

SETTING REACTIONCrosslinking reaction of a vinyl terminated dimethyl polysiloxaneCatalysed by chloroplatinic acid. Hydroen gas can be released asas by-product. The more contemporary products have hydrogen gas scavengers.

VISCOSITIESPuttyMonophaseHeavyIntermediateLight

PVS – Setting Reaction

Mandikos 1992

PolyVinyl Siloxanes

ADVANTAGESVery stable dimensionallyImpression re-pours possibleOdor and taste neutralGood elastic recoveryGood tear strengthGood wetting of prep surfaceGood working and setting timesExcellent delivery systems

Poly-Vinyl Siloxanes

DELIVERY SYSTEMS

Automix System

Pentamix System

Poly-Vinyl Siloxanes

PROBLEMSSetting retardation via sulfur in latex glovesSetting retardation from sulfur in Astringident solutionTearing of wash material away from tray materialHydrogen gas releaseLocking into undercuts and open embrasuresPorosities

COMPOSITION

Base:Polyether polymerColloidal silica fillerGlycol ether or phthalate plasticizer

Catalyst:Alkyl aromatic sulfonatePlasticizers and fillers as above

Permadyne

PENTAMIX delivery system can be used for dispensingPolyether impresssion material

Polyether based polymer cured byreaction between aziridine rings which branch off a copolymer of ethylene oxide and tetrahydrofuran

Aromatic ester(Initiator)

Cross-linking occurs via cationicPolymerisation of imine end groups

ADVANTAGESExcellent accuracy and wettingGood dimensional stabilityVery good shelf life (~ 5years, less in warm conditions)

PROBLEMSVery stiff when set / problem in undercuts, embrasuresCold disinfectionPoor tear strengthOdorPaste-paste mixing (messy, porosities)Shorter working time than PVS siliconesSensitivity to aromatic sulfonateWater condensation on chilled mixes

θ1 θ2

AB

B = Material has superior wetting, a desirable property

PVS silicones have good wetting properties and are advertised ashaving high hydrophilicity when in fact they are HYDROPHOBIC

CLINICAL TIPS TO AVOID PROBLEMSUse correct adhesive on trayBlock out locking embrasures and undercuts prior to impressionTooth surface must be cleanPreparation margins must be well defined and clear Margins free of fluids and bloodMix impression material correctlyDo not overload stock traysHave a high velocity suction handyApply material efficiently without delaysLeave in place without tray movement for correct timeRemove tray carefullyWash away any blood on impression surfaceDisinfectInspect marginal detailRetake impression if major flaws arise

Mandikos MN. Polyvinyl siloxane impression materials: An updateon clinical use. Aust Dent J 1998;43:428-34

Wassel RW, Barker D, Wall AWG. Crowns and other extra oral restorations.Impression materials and technique. British Dental Journal 2002;192:679-690

ReferencesReferences

1. 1. MandikosMandikos MN. Polyvinyl MN. Polyvinyl siloxanesiloxane impression materials: An updateimpression materials: An updateon clinical use. on clinical use. AustAust Dent J 1998;43:428Dent J 1998;43:428--34342. 2. WasselWassel RW, Barker D, Wall AWG. Crowns and other extra oral RW, Barker D, Wall AWG. Crowns and other extra oral

restorations.restorations.Impression materials and technique. British Dental Journal Impression materials and technique. British Dental Journal

2002;192:6792002;192:679--6906903. Mc 3. Mc CabeCabe JF, Wall AWG. (1998) Applied dental materials, 8th edition. JF, Wall AWG. (1998) Applied dental materials, 8th edition.

Blackwell ScienceBlackwell Science4. 4. ShillingburgShillingburg HT, HT, SumiyaSumiya H, H, WhittsettWhittsett 3rd edition. Fundamentals of 3rd edition. Fundamentals of

fixwdfixwd prosthodonticsprosthodontics. Quintessence books. Quintessence books5. 5. RosenstielRosenstiel, Land, Fujimoto. Contemporary fixed , Land, Fujimoto. Contemporary fixed prosthodonticsprosthodontics 3rd 3rd

editionedition6. Lectures from Dr tom 6. Lectures from Dr tom BerekallyBerekally. Consultant . Consultant prosthodontistprosthodontist/lecturer /lecturer

University of Adelaide, South AustraliaUniversity of Adelaide, South Australia