Impression Impression MaterialsMaterials

DH 363DH 363

Dental Materials IDental Materials I

ObjectivesObjectives List the oral structures for which impressions are madeList the oral structures for which impressions are made Differentiate between a model, cast and dieDifferentiate between a model, cast and die Describe the various types of impression traysDescribe the various types of impression trays Describe the composition and setting mechanisms of Describe the composition and setting mechanisms of

various impression materialsvarious impression materials Differentiate between elastic and non-elastic Differentiate between elastic and non-elastic

impression materials, and between reversible and non-impression materials, and between reversible and non-reversible impression materialsreversible impression materials

Describe the effect of water temperature on the setting Describe the effect of water temperature on the setting rate of alginaterate of alginate

Describe the effect of water and heat on the setting Describe the effect of water and heat on the setting rate of polysulfidesrate of polysulfides

Describe the use of impression materials with indirect Describe the use of impression materials with indirect restorative proceduresrestorative procedures

Impression MaterialsImpression Materials Used to make replicas of teeth and other Used to make replicas of teeth and other

oral tissues oral tissues Replicas used to construct restorations and Replicas used to construct restorations and

other appliancesother appliances Impression must be an accurate duplicationImpression must be an accurate duplication

Stable enough to allow disinfection and Stable enough to allow disinfection and production of a model/castproduction of a model/cast

Not all impression materials are compatible Not all impression materials are compatible with all model materials with all model materials

Wide variety of products available to make Wide variety of products available to make impressions of oral tissues. impressions of oral tissues.

ClassificationClassification

Impression TraysImpression Trays

Disposable – plasticDisposable – plastic Reusable – metalReusable – metal Stock trays – off the shelfStock trays – off the shelf

Custom trays – most accurateCustom trays – most accurate Preliminary model taken with stock trayPreliminary model taken with stock tray Made on a model of the patient’s arch Made on a model of the patient’s arch Acrylic or other resinAcrylic or other resin Custom tray used to take final Custom tray used to take final

impressionimpression

More TraysMore Trays

Bite registration tray – used Bite registration tray – used to record occlusal surfaces of to record occlusal surfaces of both arches and relate upper both arches and relate upper and lower casts in the lab and lower casts in the lab just as they relate in the just as they relate in the mouthmouth

Triple tray – used to take Triple tray – used to take impression, bite registration impression, bite registration & opposing impression all at & opposing impression all at the same timethe same time

ClassificationClassification

Chemical reaction Chemical reaction ThermosetThermoset Chain lengthening, cross-linking or bothChain lengthening, cross-linking or both

Physical changePhysical change ThermoplasticThermoplastic Cooling Cooling

Solidification (hot wax sets up)Solidification (hot wax sets up) Gelation (Jell-O)Gelation (Jell-O)

Thermoplastic not as stable as thermoset Thermoplastic not as stable as thermoset materialsmaterials

ClassificationsClassifications

Elastic – for impressions with teeth Elastic – for impressions with teeth presentpresent

Inelastic – for edentulous impressionsInelastic – for edentulous impressions

AccuracyAccuracy Procedure determines which one to useProcedure determines which one to use

Flow and detail reproductionFlow and detail reproduction Variety of viscosities availableVariety of viscosities available Light body (runny) to putty (thickest)Light body (runny) to putty (thickest)

Inelastic Impression Inelastic Impression MaterialsMaterials

PlasterPlaster Same setting reaction and properties as gypsum Same setting reaction and properties as gypsum

products used for models/castsproducts used for models/casts Major use is for edentulous ridgesMajor use is for edentulous ridges

WaxWax First material used in dentistryFirst material used in dentistry Cheap, clean, easy to useCheap, clean, easy to use Thermoplastic materialThermoplastic material May be used for impressions for complete May be used for impressions for complete

denturesdentures Mainly used in fabrication of crowns, bridges, Mainly used in fabrication of crowns, bridges,

and other restorationsand other restorations

CompoundCompound

Impression compoundImpression compound Wax with a filler added to improve Wax with a filler added to improve

handling and stabilityhandling and stability Stronger and more brittle than waxStronger and more brittle than wax Stiff thermoplastic material used for Stiff thermoplastic material used for

preliminary impressions for full preliminary impressions for full denturesdentures

Denture with green stick compound Denture with green stick compound

ZOEZOE

Zinc oxide eugenol Zinc oxide eugenol (ZOE)(ZOE) Two paste system: Two paste system:

Eugenol + fillers Eugenol + fillers and ZO powder and ZO powder mixed with mixed with vegetable oilvegetable oil

Inexpensive and Inexpensive and easy to use -- easy to use -- denturesdentures

Aqueous Elastomeric Aqueous Elastomeric MaterialsMaterials

Agar or reversible hydrocolloidAgar or reversible hydrocolloid Requires special equipmentRequires special equipment Rubbery material (gel) is boiled to Rubbery material (gel) is boiled to

become viscous liquid (sol)become viscous liquid (sol) Material then kept at 150º water bath, Material then kept at 150º water bath,

then just before use is ‘tempered’ at 110º then just before use is ‘tempered’ at 110º Impression trays use water circulating Impression trays use water circulating

through tubes to cool material in the through tubes to cool material in the mouth more quicklymouth more quickly

Inexpensive, accurate impressionsInexpensive, accurate impressions

HysteresisHysteresis

Unlike common phase changes of water Unlike common phase changes of water that freezes, melts, boils at the same that freezes, melts, boils at the same temperaturetemperature

Reversible hydrocolloid does not melt at Reversible hydrocolloid does not melt at the same temperature at which it gels.the same temperature at which it gels.

Characteristic of having different Characteristic of having different properties that depend on the direction of properties that depend on the direction of the change is called the change is called hysteresis.hysteresis.

Hydrophilic PropertiesHydrophilic Properties Reversible and irreversible hydrocolloids are mostly Reversible and irreversible hydrocolloids are mostly

waterwater AdvantagesAdvantages

Will wet tooth surfaces and even absorb Will wet tooth surfaces and even absorb some oral fluidssome oral fluids

Pouring models is easier than with Pouring models is easier than with elastomeric materialselastomeric materials

DisadvantagesDisadvantages Evaporation – shrinkageEvaporation – shrinkage Syneresis – contraction and exude waterSyneresis – contraction and exude water Imbibition – absorb, swell and distortImbibition – absorb, swell and distort

Alginate Impression Alginate Impression MaterialsMaterials

Alginate Alginate impression impression materials are materials are commonly used commonly used in general in general dentistrydentistry

Advantages of AlginatesAdvantages of Alginates Common method for Common method for

obtaining diagnostic castsobtaining diagnostic casts Easy to manipulateEasy to manipulate Comfortable for patientsComfortable for patients Relatively inexpensiveRelatively inexpensive Do not require special Do not require special

equipment equipment Alginate materials are Alginate materials are

supplied as powders that supplied as powders that are mixed with waterare mixed with water

Disinfectants can be addedDisinfectants can be added

Impression IngredientsImpression Ingredients

Diatomaceous Earth provides body for the impression Diatomaceous Earth provides body for the impression Key components: K+ alginate derived from algae Key components: K+ alginate derived from algae

(carbohydrate polymer) & CaSO4 (reactor)(carbohydrate polymer) & CaSO4 (reactor) Carboxylate groups react with calcium ions and cross-Carboxylate groups react with calcium ions and cross-

link the material to form a gel -- link the material to form a gel -- irreversible irreversible hydrocolloidhydrocolloid

Reactor is same chemical component as in gypsum Reactor is same chemical component as in gypsum (used in making cast from the alginate impression)(used in making cast from the alginate impression)

AlginatesAlginates

Packaged in Packaged in canisters, pouches canisters, pouches or individual or individual pouchespouches

Clinical Problems?Clinical Problems?

Alginates:Alginates:1.1. Tear easily if the walls of the impression Tear easily if the walls of the impression

become too thin.become too thin.2.2. Lack the detail of other impression materials. Lack the detail of other impression materials.3.3. Can distort easily if removed too soon after Can distort easily if removed too soon after

placement or if removed too slowly.placement or if removed too slowly.4.4. Can have varying setting time based on Can have varying setting time based on

many factors. It’s a good idea to follow the many factors. It’s a good idea to follow the manufacturer’s instructions to achieve manufacturer’s instructions to achieve

optimal optimal consistency. (Inoue et al., 1999)consistency. (Inoue et al., 1999)

Alginate Impression Alginate Impression Temperature of the Temperature of the

water controls the water controls the setting reactionsetting reaction Cooler water slows Cooler water slows

the reactionthe reaction Warmer water Warmer water

hastens the hastens the reactionreaction

Fast set – 1-2 minutesFast set – 1-2 minutes Regular set – 3-4 Regular set – 3-4

minutesminutes

9 month 9 month set??set??

StorageStorage

Consistency of the alginate material prior Consistency of the alginate material prior to taking the impression significantly to taking the impression significantly effects accuracy. (Inoue et al., 1999)effects accuracy. (Inoue et al., 1999)

Storage of impression in 100% humidity Storage of impression in 100% humidity recommended for greatest accuracyrecommended for greatest accuracy

Some research indicates that disinfection Some research indicates that disinfection of impressions by immersion in certain of impressions by immersion in certain disinfectants can be just as accurate.disinfectants can be just as accurate.

SummarySummary Alginates are the most common method for Alginates are the most common method for

obtaining diagnostic casts.obtaining diagnostic casts. The two main components K+ alginate The two main components K+ alginate

(carbohydrate polymer) & CaSO4 (reactor) (carbohydrate polymer) & CaSO4 (reactor) react to form a gel--->irreversible hydrocolloid.react to form a gel--->irreversible hydrocolloid.

Be aware of clinical problems you may Be aware of clinical problems you may encounter using alginates and take the encounter using alginates and take the necessary precautions to avoid them.necessary precautions to avoid them.

Accuracy of your impressions can be affected Accuracy of your impressions can be affected greatly by the alginate gaining or losing water. greatly by the alginate gaining or losing water. Initial consistency of the material is also Initial consistency of the material is also important to the accuracy of the impression.important to the accuracy of the impression.

PolysulfidesPolysulfides

First non-aqueous elastomeric First non-aqueous elastomeric material developed for dentistrymaterial developed for dentistry

Often called ‘rubber’ or ‘rubber base’Often called ‘rubber’ or ‘rubber base’ Uses specific adhesive in the trayUses specific adhesive in the tray Set via condensation polymerization Set via condensation polymerization

– chemical reaction– chemical reaction Water most common by-product Water most common by-product

(‘condensation’ polymerization)(‘condensation’ polymerization)

Mixing PolysulfidesMixing Polysulfides

Two paste system (white base and Two paste system (white base and brown accelerator)brown accelerator) Equal lengths dispensed on mixing padEqual lengths dispensed on mixing pad Pastes are swirled and stropped togetherPastes are swirled and stropped together Mixed material is place in tray and the Mixed material is place in tray and the

impression takenimpression taken Much more accurate than alginate Much more accurate than alginate

(advantage)(advantage) Long working time (advantage)Long working time (advantage) Icky smell and taste (disadvantage)Icky smell and taste (disadvantage) Long setting time (disadvantage)Long setting time (disadvantage)

Condensation SiliconesCondensation Silicones

Based on silicone rubberBased on silicone rubber HydrophobicHydrophobic Condensation reactionCondensation reaction Alcohol by-productAlcohol by-product Cleaner than rubber, but hard to Cleaner than rubber, but hard to

pour good modelspour good models Not used much anymoreNot used much anymore

PolyethersPolyethers

Developed in the late ’60’sDeveloped in the late ’60’s Cationic polymerization – similar to Cationic polymerization – similar to

addition polymerization except a positive addition polymerization except a positive ion is the reactive moleculeion is the reactive molecule

No reaction by-productsNo reaction by-products Shorter working and setting timesShorter working and setting times Very accurate and easy to pour with Very accurate and easy to pour with

gypsumgypsum ImpregumImpregum – most popular product – most popular product

ImpregumImpregum

Addition SiliconesAddition Silicones

Most popular, Most popular, especially for C&Bespecially for C&B

Clean, no smellClean, no smell Accurate, stable, Accurate, stable,

and expensiveand expensive

Also called:Also called:

Vinyl Vinyl polysiloxanespolysiloxanes

PolyvinylsiloxanesPolyvinylsiloxanes

PolyvinylsiloxanesPolyvinylsiloxanes Reactive group is C=C Reactive group is C=C

(vinyl group)(vinyl group) Free radicals, addition Free radicals, addition

polymerization and cross-polymerization and cross-linking to form stable linking to form stable rubber materialrubber material

No evaporation, no by-No evaporation, no by-product formedproduct formed

Viscosities include:Viscosities include: Light body – usually Light body – usually

placed directly on prepplaced directly on prep Medium bodyMedium body Heavy bodyHeavy body MonophaseMonophase PuttyPutty

MixingMixing Each viscosity comes as two Each viscosity comes as two

pastespastes Mixed like rubber baseMixed like rubber base Also can be supplied in Also can be supplied in

automix gunautomix gun

Putty – used in the tray as Putty – used in the tray as ‘body’ of the impression‘body’ of the impression Mixed by kneading two colors Mixed by kneading two colors

together with fingers – no latex together with fingers – no latex gloves! Vinyl gloves OK.gloves! Vinyl gloves OK.

TimingTiming

Standard Standard procedure is procedure is critical for mixing, critical for mixing, working, and working, and setting times!setting times!

QuestionsQuestions

1.1. Why do we take alginate impressions?Why do we take alginate impressions?

2.2. What are ingredients of typical alginate What are ingredients of typical alginate impression materials and what is their impression materials and what is their source?source?

3.3. What clinical problems can occur when What clinical problems can occur when we take an alginate or other type of we take an alginate or other type of impression?impression?

4.4. What operator variable most affects the What operator variable most affects the accuracy of alginate impression accuracy of alginate impression materials?materials?