imp materials

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Impression Materials

Chapter 8

DAE/DHE 203


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Impression Materials:

Used to make replicas of oral structures Negative replica made by impression Cast material is placed into impression to yielda positive replica of the oral tissue

Allows for the indirect restoration or dental

appliance to be fabricated without the patientpresent

Variety of materials for a variety of applications


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Characteristics of

Impression Materials:

Fluid enough to flow around area of interest

Must set in reasonable amount of timeCan remove from mouth without distortionNo harmful effects on tissues

Relatively tasteless & odorlessDimensionally stable until a cast is createdGive detailed reproductionCompatible with cast materials


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Impression Trays:

Used to carry the material to pts mouth Must be sturdy enough to support the material

Need to be disposed of or sterilized after useMetallic trays are autoclavableStock trays available: full arch, quadrant

Custom trays made of acrylic for most accuracyTriple trays takes impression of opposing teeth,occlusal registration, and prep sitePerforated trays have holes for retention of

material


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Categories of Impression Materials:

INELASTIC

RigidCannot be used withundercuts

For edentulous orbite registration

ELASTIC

Flexible & rubbery Used with undercutsGenerally used todayTwo subcategories:

Hydrocolloids (Aqueous)Elastomers


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Inelastic Impression Materials:

Impression Compound

ZOE Impression PastePlaster


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Impression Compound:Resins + wax

Thermoplastic, solid materialHeat to soften materialCool to set materialPhysical change only; NO chemical reaction

Forms: plates and sticksSoften in water bath (10 warmer than body)

Applied to tray and inserted in mouth to coolUsed as a custom tray


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ZOE Impression Paste:Similar formulation as ZOE cementsPastes mixed together chemical reaction

BASE + CATALYST

Applied in thin layer in custom tray foredentulous arch; or to occlusal surfacesSets in 4 5 minutes


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Elastic Impression Materials:

Hydrocolloids:Reversible HydrocolloidsIrreversible Hydrocolloids

Elastomers:PolysulfidesPolyethersCondensation Silicones

Addition Silicones - Polyvinylsiloxanes


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Elastic Impression Materials:

HYDROCOLLOIDS water -based impression materialsColloid liquid suspension of particlesParticles derived from seaweed & kelpLiquid = water

GEL the rubber-like form of the materialSOL the material in liquid solutionNot dimensionally stable must be poured immediately


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Hydrocolloids:

Reversible Hydrocolloid: Agar a gelatinous material + waterThermoplastic NO chemical reaction

Reversible Goes from gel, to sol, and back to gel,

by raising and lowering temperature

Dispensed in tubes & syringes Very accurate final impression material


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Hydrocolloids:

Handling Reversible Hydrocolloid:Special water baths with 3 chambers are used1) Material is immersed in boiling tank (212 F)

for 10-20 minutes; turns from gel to sol2) Place in storage bath (150 F);

10 minutes to few days; remains sol3) Load tray; immerse in the tempering bath

(110 F); 5-10 minutes; lowers temp for pt comfort


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Hydrocolloids:

Handling Reversible Hydrocolloid:4) Load syringe; extrude onto prep site5) Seat tray in mouth6) Attach cooling hoses to tray7) Hold firmly in pts mouth until cooled and

transformed to gel state8) Remove from pts mouth and pour

immediately


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Hydrocolloids:

Irreversible Hydrocolloid: ALGINATE impression materialFormed by chemical reactionPowder + water; mixedNOT reversible; SOL to GEL onlyProtect from inhalationDispensed in cans or bulk packagesUsed when less detail is required


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Hydrocolloids:

Handling Alginate:Fluff powder andmeasure accuratelyMeasure water temp!Mix in a flexible,rubber bowlStir to wet powderStrop mixture againstside of bowl to eliminateair bubblesMix until creamy &

homogeneous; 60 sec.


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Hydrocolloids:

Handling Alginate:Load alginate into trayfrom posteriorPress material into trayto eliminate voidsSmooth & indentalginate with wet fingerUse extra alginate towipe onto occlusalsurfaces of teeth


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Evaluating an Alginate Impression:

Full coverage, including retromolar areaTray centeredClear & sharp impressionNo voids, air bubbles, or tearsHas a peripheral roll (vestibular area)

If all is OK, rinse & disinfect impression,pour-up in stone/plaster, or store in humid bag.


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Irreversible Hydrocolloid:

Advantages:

Easy & economicalMany applicationsPatient comfortExcellent wetting bygypsumDisposable tray

Disadvantages:

Not enough detailfor final impressionMust be poured

immediately


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Hydrocolloids:

SYNERESIS shrinkage in impression due to loss

of water from heat or exposure to air.

IMBIBITION swelling of impression due totaking up moisture

To avoid these conditions (dimensional distortion),pour-up immediately!


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Elastomers:

Two-paste systems:Two tubes pastes mixed by hand

Two putties mixed/kneaded by handCartridge & Extruder Gun automix tips usedCartridge & Motor-driven Mixer automix tips used

Set by chemical reactionWarmth and moisture may slow settingMust use a tray adhesive (if tray not perforated)Latex may inhibit set of polyvinylsiloxanes


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Elastomers:

Elastomers are used in a two-step process:Preliminary Impression - the material used to

form the base or the tray material used in animpression; usually more viscous or heavy-body

Secondary or Wash Impression the materialapplied through a syringe around the prep sitefor detail; usually less viscous;light or medium -body.


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Elastomers:

POLYSULFIDE:Oldest elastomeric used in dentistryTwo pastes mix base with catalystLiquid polymer with sulfhydryl group contains sulfur

rubber -base impression materialUsed best with custom traysOther materials have replaced this one


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Elastomers:

Handling Polysulfides:1.

Equal lengths of pastes on pad2. Pastes are swirled together, then stropped3. Material placed in custom tray4. Take impression hold in place for up to 15 min.5. Remove from pts mouth slow & steady force6. Rinse & disinfect7. Pour-up impression within several hours


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Polysulfides:

Advantages:

EconomicalGood tear resistanceGood compatibility

with gypsum

Disadvantages:

MalodorStains clothingLong setting time

Fair stabilityLess accurate


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Elastomers:

Condensation Silicones:Similar to silicone rubber products (but non-toxic)Setting by-product of alcohol

Hydrophobic results in voids in stoneShrinkage occurs as it setsMust be poured immediately

Accurate, but slow setting timeReplaced by improved products


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Elastomers:

POLYETHERS:Developed in 1960s No reaction by-product producedShorter working and setting timeOnly come in a single viscosityStiff material can use a triple tray

Very popular Impregum No need to pour-up immediately


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Elastomers:

Handling Polyether:1. Mix equal lengths of paste; or extrude

through the automix cartridge tip2. Load syringe and apply to tooth thru tip3. Load tray and invert over area for

impression4. Allow to set; 4 5 minutes5. Remove from mouth6. Rinse & disinfect


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Polyether: Impregum


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Elastomers:

ADDITION SILICONES: Polyvinylsiloxanes silicone polymerTwo pastes or two puttiesHydrophobic by nature manufacturersadding components to increase wettability

Very accurate & fast setting Avoid contact with latex (gloves, rubber dams)Low setting shrinkage & very stable


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Elastomers:

Handling Addition Silicone:Mix equal lengths ofpastes, or automix

Apply light-body materialto tooth thru syringe

Load tray with heavy-bodySet tray over prep siteSet in 4 5 minutesRinse & disinfect


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Addition Silicone: Polyvinylsiloxane

Advantages:

Very stableShort setting timeGood tear resistance

Great accuracyNo bad taste

Disadvantages:

May have poorwettabilityTwo pastes to mix

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