Impression Materials

Dr M Slabbert Dept Prosthodontics Wits

First Impressions count

Classification of ImpressionsPreliminary impressions

Taken either by the dentist or an expanded-function dental assistant.

Used to make a reproduction of the teeth and surrounding tissues.

Used to make (1) diagnostic models, (2) custom trays, (3) provisional coverage, (4) orthodontic appliances, and(5) pretreatment and post‑treatment records.

Classification of Impressions cont’dFinal impressions

Taken by the dentist.Used to make the most accurate reproduction of

the teeth and surrounding tissues.Used to make indirect restorations, partial or full

dentures, and implants.

Classification of Impressions cont’dBite registrations

Taken by the dentist or dental assistant.Make a reproduction of the occlusal relationship

between the maxillary and mandibular teeth.Provide an accurate registration of the patient’s centric

relationship between the maxillary and mandibular arches.

Oral Oral ExaminationExamination

Primary Impression

Study model (cast)

Treatment Planning• duplicate model

Mouth and tooth preparation

Final Impression

Master modelMaster model

Laboratory procedure• investment cast• refractory cast

Denture

DeliveryDelivery

An impression is a negative record of the tissues of the oral cavity which constitutes the basal seat of the denture. An impression is made in a material which has plasticity

and which hardens or sets while in contact with the tissue.

Prof Owen Fundamentals of Removable partial dentures 2nd Ed pg. 124 -131

Wits Pros Book Vol 2 Pg. 14

Study pages 14- 31 Vol 2

www.health.wits.ac.za/Prosthodontics Primary impressions in alginate…

Definition

The Ideal Impression Material Easy to mix and handle.

Suitable working time.

Suitable setting time.

Compatible with die and stone

Not toxic or allergenic to the patient.

Dimensionally stable on setting.

Accurate to record the fine details of the prepared tooth

Has acceptable odor and taste.

Adequate strength.

Adequate shelf life.

The Ideal Impression Material cont. Economical

Ready to disinfected without loss of accuracy.

Fluid or plastic when inserted into the mouth.

It must be an exact record of all the aspects of the prepared tooth and sufficient unprepared tooth structure immediately adjacent to margins, to allow the dentist and the technician to be certain of the location and configuration of the finish line.

Other teeth and tissue surrounding the abutment tooth must be accurately reproduced to permit proper articulation of the cast and contouring of the restoration.

It must be free from air bubbles especially in the finish line area.

• High accuracy Biocompatibility

(very small contraction <0.5%)

• High dimensional stability Compatibility to stone• High elastic recovery High tear strength• Ease of use Long shelf life• Hydrophilic Pleasant color &taste

and Hydrophobic• Proper setting time Cost

Elastic recoveryThe amount of rebound after a cylinder of material is strained 10% for 30 seconds.

98%

Hydrophilic VS Hydrophobic

Which one of the impression Which one of the impression materials we choose? materials we choose?

•What’s the job you do?

primary impression

final impression

•How accurate do you want?

removable denture

fixed prostheses

•What technique do you use?

Impression

Impression Tray

IMPRESSION MATERIALSIMPRESSION MATERIALSKey PropertiesKey Properties

Accuracy

a. Accuracy = ability to replicate the intraoral surface details.

DimensionalStability

b. Dimensional Stability = ability to retain its absolute dimensional size over time.

TearResistance

c. Tear Resistance = ability to resist tearing in thin sections (such as through the feather-edged material within the gingival sulcus.

PROBLEM ANALYSISPROBLEM ANALYSISWhat are tolerable limits for “error” in indirect procedures?

a. Impressions = b. Casts, Dies =c. Waxing =d. Investing =e. Casting =f. Finishing, Polishing =g. Cementation =

+/- 0+/- 0+/- 0+ 1.5% 1.5%+/- 0+/- 0

PreppedToothWidth

8 mm (=8,000 m)

8,000 m x 0.5% = 40 m = 20 m/sideTypical clinical error = >100 m/side

Properties: Reaction: Set:Rigid:1. Impression Plaster Rigid Irrev (Chem)2. Impression Compound Rigid Rev (Phys)3. Zinc Oxide/ Eugenol Rigid Irrev (Chem)

CLASSIFICATION SYSTEMCLASSIFICATION SYSTEMBased on Properties of Set Materials

Water-Based Gel:4. Alginate (Irreversible Hydrocolloid) Flexible Irrev (Chem)5. Agar-Agar (Reversible Hydrocolloid) Flexible Rev (Phys)

Elastomers:6. Polysulfide (Rubber Base, Thiokol) Flexible Irrev (Chem)7. Silicone (Conventional, Condensation) Flexible Irrev (Chem)8. Polyether Flexible Irrev (Chem)9. Polyvinyl Siloxane (Addition Silicone) Flexible Irrev (Chem)

Impression materials

Impression materialImpression material

ElasticElastic

NonelasticNonelastic

Zinc oxide EugenolZinc oxide Eugenol

Impression CompoundImpression Compound

PlasterPlaster

Non-aqueouselastomers

Non-aqueouselastomers

PolyethersPolyethers

Additionsilicone

Additionsilicone

Condensationsilicone

Condensationsilicone

PolysulfidesPolysulfides

Impression waxes Impression waxes

HydrocolloidsHydrocolloids

AgarReversible

AgarReversible

AlginateIrreversible

AlginateIrreversible

NonelasticNonelastic

Zinc oxide eugenolZinc oxide eugenol

Impression CompoundImpression Compound

Gypsum (Plaster)Gypsum (Plaster)

Impression waxImpression wax

Dental Plaster• Type I – impression plaster• Type II – model (laboratory) plaster (used for mounting casts)plaster is composed of the β form of calcium sulfate hemihydrate Crystals•plaster is weaker than dental stone due to:

1.) porosity of the particles, requiring more water for a plaster mix2.) irregular shapes of particles prevent them from fitting together tightly

Dental Stone• Type III - dental stone(diagnostic casts)• Type IV - high strengthdental stone (workingmodels)• Type V - high-strength, high-expansion dental stone

Stone is the α hemihydrate form Types of Gypsum Products

Dental Plaster

Calcination Calcination

H or other meansMineral gypsum ---------------- > Model plaster + Water(CaSO4 . 2H2O) Dental stone High-strength dental stone (CaSO4 . 1/2H2O)

Reverse Reaction

When calcium sulphate hemihydrate (dental plaster, stone, etc.) is mixed with water, the reverse reaction takes place, and the hemihydrate is converted back to the dihydrate:

CaSO4 . 1/2H2O + 11/2H2O ---> CaSO4 . 2H2O + 3900 cal/g mol

Elastomeric Impression Materials

A material that is used when an extremely accurate impression is essential. The term elastomeric means having elastic or rubberlike qualities.

ElasticElastic

HydrocolloidsHydrocolloids

AgarAgar

AlginateAlginate

Hydrocolloids

Reversible and Irreversible Introduced by Sears 1939 First elastic Sears AW. Hydrocolloid impression technique for inlays and fixed

bridges. Dent Digest 1937; 43: 230-234.Lin C, Zeiber G J. Accuracy of impression materials for complete

arch fixed partial dentures. J Prosthet Dent 1988; 59: 288-291Philips Science of Dental Materials 11th Ed. Part 2 Pg. 231

Irreversible Hydrocolloid Material that cannot return to a solution state

after it becomes a gel.Alginate is the irreversible hydrocolloid most

widely used for preliminary impressions.

Makeup of AlginatePotassium alginate (Alginic Acid) (12-15%)

Comes from seaweed; is also used in foods such as ice cream as a thickening agent.

Calcium sulfate (8-12%)Reacts with the potassium alginate to form the gel.

Trisodium phosphateAdded to slow down the reaction time for mixing.

Makeup of Alginate cont’dDiatomaceous earth (70%)

A filler that adds bulk to the material. Controls the stiffness of the set gel

Zinc oxideAdds bulk to the material.

Potassium titanium fluoride (~10%)Added so as not to interfere with the setting and surface

strength. Sodium Phosphate (retarder) (2%)

Coloring and flavouring agents (traces)

Physical Phases of Alginate

The first phase is a sol (as in solution). In the sol phase, the material is in a liquid or semiliquid form. (sol: resembles a solution, but is made up of colloidal particles dispersed in a liquid)

The second phase is a gel. In the gel phase, the material is semisolid, similar to a gelatin dessert.

“gel” entangled framework of solid colloidal particles in which liquid is trapped in the interstices and held by capillary forces (Jello)

Packaging and Storing of AlginateContainers about the size of a coffee can are the

most commonly used form of packaging. Premeasured packages are more expensive, but

save time by eliminating the need for measurement of the powder.

Shelf life of alginate is approximately 1 year.

Causes for Distortion and Dimensional Change of Alginate

If an alginate impression is stored in water or in a very wet paper towel, the alginate will absorb additional water and expand. This condition is called imbibition.

If an alginate impression remains in the open air, moisture will evaporate from the material, causing it to shrink and distort. This condition is called syneresis.

ADA Specifications <3% deformation with a 10% strain

Altering the Setting Times of AlginateCooler water can increase the setting time if

additional time is needed for the procedure. Warmer water can reduce or shorten the setting

time of the procedure.

Water-to-Powder Ratio An adult mandibular impression generally

requires two scoops of powder and two measures of water.

An adult maxillary impression generally requires three scoops of powder and three measures of water.

Taking an Alginate Impression

Explain the procedure to the patient:The material will feel cold, there is no unpleasant taste,

and the material will set quickly.Breathe deeply through your nose to help you relax and be

more comfortable.Use hand signals to communicate any discomfort.

Mouth Preparation

Rinse and dry the patient's teeth If teeth are too dry, alginate will stick

An Acceptable Alginate Impression The impression tray is centered over the central and

lateral incisors. There is a complete "peripheral roll," which includes all of

the vestibular areas. The tray is not "overseated," which would result in

exposure of areas of the impression tray.The impression is free from tears or voids.There is sharp anatomic detail of all teeth and soft

tissues.The retromolar area, lingual frenum, tongue space, and

mylohyoid ridge are reproduced in the mandibular impression.

The hard palate and tuberosities are recorded in the maxillary impression.

Trouble Shooting Inadequate working or setting time:

temperature of the water, incomplete spatulation W/P too low improper storage of alginate powder

Distortion: Tray movement during gelation or removed from mouth prematurely weight of tray compressing or distorting alginate

impression not poured up immediately

Tearing: removing impression from mouth before adequately set thin mixes (high W/P ratio) presence of undercuts (blocking out these areas before an impression may help) inadequate amount of impression material in tray (avoided by minimum 3 mm of impression

material between tray and oral tissues)

• Loss of detail: removed from mouth prematurely

Consistency: preset mix is too thin or thick The W/P ratio is incorrect (avoid by fluffing powder before measuring;

do not overfill powder dispenser) inadequate mixing (avoided by vigorous spatulation and mixing for

recommended time) using hot water: grainy and prematurely thick mix

• Dimensional change: delay in pouring alginate impression stored in air: results in distorted, undersized cast

due to alginate impressions losing water when stored in air

Porosity: whipping air into the mix during spatulation (proper mixing: after initial wetting of powder by the water, mix alginate so as to squeeze the

material between the spatula blade and the side of the rubber bowl)

• Poor stone surface (of cast) set gypsum remaining in contact with the alginate for too long a period

of time

Reversible Hydrocolloid An impression material that changes its physical

state from a sol to a gel and then back to a sol.

Chemical Makeup of Reversible Hydrocolloid

85% water13% agar

Agar is an organic substance derived from seaweed.Additional chemical modifiers are added to aid in the

handling characteristics.

Conditioning Bath for Reversible Hydrocolloid

The first bath is for liquefying the semisolid material. A special water bath called a “hydrocolloid conditioner” at 212° F liquefies the material. After liquefying, the preset thermostat cools the temperature to 150° F automatically.

The second bath becomes a storage bath that cools the material, readying it for the impression. At this temperature, the tubes are waiting for use.

A third bath is kept at 110° F/44° C for tempering the material after it has been placed in the tray.

Three Compartments Three Compartments

Types of Reversible Hydrocolloid Tray material

Packaged in plastic tubes. Each tube has enough material to fill a full arch, water-cooled tray.

Syringe materialPackaged in plastic or glass cartridges that fit a

syringe or in preloaded syringe or preformed sticks that refill special hydrocolloid inlay syringes.

Application of Reversible Hydrocolloid Impression Material

1. A stock water-cooled tray is selected, making sure that the tray does not impinge on any of the teeth or soft tissue.

2. Plastic stops are placed in the tray.3. Tubing is connected to the tray and to the water

outlet for drainage.4. The material is liquefied and moved to the storage

bath.5. The light-bodied material is placed in the syringe,

and heavy-bodied material is placed in the tray.6. The light-bodied material is expressed around the

prepared tooth, and the dentist seats the tray.

Non-aqueouselastomers

Non-aqueouselastomers

PolyethersPolyethers

Additionsilicone

Additionsilicone

Condensationsilicone

Condensationsilicone

PolysulfidesPolysulfides

ElasticElastic

1. Flexible Matrix (Continuous Phase):a. Multifunctional Pre-Polymer or Polymerb. Crosslinking Agentc. Curing Agent (Catalyst or Initiator)d. Modifiers (Accelerators, Retarders,

Plasticizers, Flavoring Agents, Colorants)

2. Filler or Extender (Dispersed Phase):

GENERAL FORMULATIONGENERAL FORMULATIONFor Elastic Impression MaterialsFor Elastic Impression Materials

Polymer (high shrinkage)

Filled Polymer (low shrinkage)

ImpressionImpression

During setting shrinkage, distortion of impression is toward tray.

Dies tend to be oversize and so the casting is oversize.

ELASTOMERIC IMPRESSIONSELASTOMERIC IMPRESSIONSManagement of ShrinkageManagement of Shrinkage

Impression

Impression TrayUse 2-step techniques:

(a) Light-Heavy Body, OR(b) Wash-Putty

Load tray withheavy-bodied IM

Cover prep withlight-bodied IM

from syringe

ELASTOMERIC MATERIALSELASTOMERIC MATERIALSMixing and Delivery Systems

Mixing Options: 2 Pastes on Mixing Pad 2 Pastes in Mixing Gun 2 Pastes in Mixing Machine

2x2x2x2x2x2x2x2 = 256 folds2x2x2x2x2x2x2x2 = 256 foldsPolysulfide Rubber,

Silicone Rubber

Polyether,Polyvinylsiloxane

IMPRESSION MATERIALSIMPRESSION MATERIALSManagement of Distortion During Tray Removal

Impression

Impression Tray

VERYFAST

(SNAP)

Strain rate sensitive elastomers !

Fast removal

Slow removal

IMPRESSION MATERIALSIMPRESSION MATERIALSDistortion Time Related to Setting Reaction

VPS Pe PS, Silicone100

log TIME (minutes)

RE

AC

TIO

NC

ON

VE

RS

ION

(%

)

Polysulfide Impression MaterialChemical makeup

Base: Mercaptan polysulfide.Cross-linking agent: Sulfur and/or lead peroxide.Catalysts: Copper hydroxides, zinc peroxide, organic

hydroperoxide.Fillers: Zinc sulfate, lithopone, or calcium sulfate

dihydrate.

Manipulation and Technique Considerations for Polysulfide Material Dispense pastes at the top of the mixing pad. Mix pastes with the tip of a spatula to incorporate the

material first.Transfer the material to the fresh surface of the mixing pad. Water, saliva, and blood affect polysulfide material. Impression should be removed quickly after settingdo not

rock the tray. Adhesive must be thin and dry before adding the

impression material. Wait 20 to 30 minutes before pouring the impression for the

stress relaxation to occur in the material.Be careful of glove powder contamination of the

impression.

Polyether Impression Material

Chemical makeupBase: PolyetherCross-linking agent: SulfateCatalysts: Glycol-based plasticizers Filler: Silica

Manipulation and Technique Considerations for Polyether Material Material is very stiff, which makes it difficult to

remove without rocking.When removing the impression, break the seal and

rock slightly to prevent tearing. Water, saliva, and blood affect polyether material. Added moisture will increase the impression’s

marginal discrepancy. Increased water absorption occurs if a thinning

agent is used.

Silicone Impression MaterialChemical makeup

Base: Poly dimethyl siloxaneCross-linking agent: Alkyl ortho silicate or organo

hydrogen siloxaneCatalyst: Organo tin compoundsFiller: Silica

Manipulation and Technique Considerations for Silicone Material The material has a limited shelf life. The tray requires a special tray adhesive. No syneresis or imbibition but does respond with

shrinkage over time. The material is more flexible, so there is more

chance for distortion during removal. Wait 20 to 30 minutes before pouring of models for

stress relaxation to occur.

Polyvinyl Siloxane Impression MaterialChemical makeup

Base: Silicone polymCatalyst: Chloroplatinic acidFiller: Silica

For dimensional stability, this is the best impression material.

Pouring of the model can be delayed up to 7 to 10 days.

Stiffness of the material makes removal of the tray difficult.

Material dispensed using auto-mixing unit and mixing tips.

Manipulation and Technique Considerations for Polyvinyl Siloxane

Material

Manipulation and Technique Considerations for Polyvinyl Siloxane

Material

CONTINUOUS PHASE:Polymer = Mercaptan Functional PolysulfideCrosslinking Agent = Sulfur and/or Lead PeroxideCatalysts = PbO2 or Copper Hydroxides (Type I)

Zinc Peroxide or Organic Hydroperoxide (Type II)

DISPERSED PHASE:Fillers = TiO2 or Zinc Sulfate or

Lithopone or Calcium Sulfate Dihydrate

SETTING REACTION:Stepwise (relatively slow), Exothermic, Affected by temperature

POLYSULFIDE RUBBERPOLYSULFIDE RUBBERChemistry and Setting ReactionChemistry and Setting Reaction

POLYSULFIDE RUBBERPOLYSULFIDE RUBBERManipulation and Technique ConsiderationsManipulation and Technique Considerations

a. Two-step techniques recommended: Reduces air entrapment andsurface tension effects.

b. Material adversely affected by H2O, saliva, and blood.c.* Set impression should be removed quickly - do not rock tray.d. No syneresis or imbibition, but distortion due to continued reaction.e. Ideally need uniform thickness and at least 2 mm thick for accuracy.

(1) Adhesive must be thin(2) Adhesive must be dry

f. Paste-Paste Mixing Recommendations:(1) Dispense pastes at the top of the mixing pad(2) Mix pastes with tip of spatula only for 5 seconds(3) Transfer mass to fresh surface at center of mixing pad(4) Wipe spatula off with paper towel; Strop mass for 15s to constant color(5) Load syringe or tray(6) Use pad excess to monitor setting time

g. Pouring of models:(1) Wait 20-30 minutes before pour for stress relaxation to occur(2) RB is non-reactive with model and die materials(3) Be careful of glove powder contamination of impression(4) RB can be electroplated

SILICONE RUBBERSILICONE RUBBERChemistry and Setting ReactionChemistry and Setting Reaction

CONTINUOUS PHASE:Polymer = Polydimethyl SiloxaneCrosslinking Agent = Alkyl Orthosilicate or Organo H-SilaneCatalysts = Organo Tin Compounds (e.g., tin octoate)

(but not dibutyl tin dilaurate)Modifiers = Colorants, Flavorants

DISPERSED PHASE:Fillers = Silica

SETTING REACTION:Stepwise (relatively slow), Exothermic, Affected by temperatureH2O by-products

SILICONE RUBBERSILICONE RUBBERManipulation and Technique ConsiderationsManipulation and Technique Considerations

a. Limited shelf-life: Unstable in tubes.b. Requires mechanical retention or special tray adhesivesc. No syneresis or imbibition, but continued polymerization shrinkage.d. Better dimensional stability than RHC but more expensivee. Pouring of models:

(1) More flexible so more chance for distortion during removal(2) Wait 20-30 minutes before pour for stress relaxation to occur

POLYETHER RUBBERPOLYETHER RUBBERChemistry and Setting ReactionsChemistry and Setting Reactions

CONTINUOUS PHASE:Polymer = Amine-terminated PolyetherCrosslinking Agent = Aromatic SulfonateCatalysts =Modifiers = Colorants, Glycol Plasticizers, Flavorants

DISPERSED PHASE:Fillers = Silica

SETTING REACTION:Stepwise (relatively slow), Exothermic, Affected by temperature

POLYETHER RUBBERPOLYETHER RUBBERManipulation and Technique ConsiderationsManipulation and Technique Considerations

a. Excellent impression accuracy and dimensional stability.b. Stiff and therefore difficult to remove without rocking.c. Break seal and rock slightly to prevent tearing: Low tear resistance.d. Negatively affected by H2O, saliva, and blood.

(1) Since hydrophobic, moisture increases marginal discrepancy(2) Increased water absorption occurs if use thinning agents

e. Can be dispensed from automated extruder and mixer (ESPE PentaMix)

POLYVINYL SILOXANEPOLYVINYL SILOXANEChemistry and Setting ReactionsChemistry and Setting Reactions

CONTINUOUS PHASE:Polymer = Double-bond-functional Silicone PolymerCrosslinking Agent = Chloroplatinic AcidCatalysts =Modifiers = Colorants, Flavorants, Plasticizers

DISPERSED PHASE:Fillers = Silica

SETTING REACTION:Chain (very fast), Exothermic, Affected by temperatureHydrogen gas released by decomposition of crosslinking agent.

POLVINYLSILOXANEPOLVINYLSILOXANEManipulation and Technique ConsiderationsManipulation and Technique Considerations

a. BEST impression material for dimensional stability: Pouring should be delayed at least 4 hours for H2 out-gassing.Pouring can be delayed up to 7-to-10 days (or indefinitely).

b. Stiffness makes removal difficult.c. Most material dispensed using auto-mixing gun and mixing tips

PredominantlyPOLYSULFIDE andSILICONE elastomersbefore 1995.

COMMERCIAL PRODUCTSCOMMERCIAL PRODUCTS1980-19951980-1995

Predominantly POLYETHER andPVS elastomers after 1996.

COMMERCIAL PRODUCTSCOMMERCIAL PRODUCTS1996-20041996-2004

IMPRESSION MATERIALSIMPRESSION MATERIALSComparison of Key PropertiesComparison of Key Properties

Poor >---------------------------------> Good1. Accuracy (Reproduction of Detail):

a. Wetting of Tissues: ALG < SIL, PS < PE <= RHC, PVSb. Wetting by Dental Stone: SIL, PVS < PS < PE <= ALG, RHC

2. Dimensional Stability: ALG <= RHC < PS, SIL < PE, PVS (Resistance to Distortion):a. Polymerization Shrinkageb. Thermal Shrinkagec. Loss of Components d. Stress Relaxation

3. Tear Resistance (Elasticity): ALG, RHC, PE < PVS , SIL < PSa. Elastic Deformationb. Strain Rate Sensitivity

IMPRESSION IMPRESSIONSIMPRESSION IMPRESSIONSDimensional Stabilty

PE

RC

EN

TC

HA

NG

E (

%)

PRODUCT EXAMPLES

Stock tray

Rim lock tray Perforated tray

Special tray(Custom tray)

Stock tray

NonelasticNonelastic

Zinc oxide eugenolZinc oxide eugenol

Impression CompoundImpression Compound

PlasterPlaster

Impression waxImpression wax

ElasticElastic

HydrocolloidsHydrocolloids

Non-aqueouselastomers

Non-aqueouselastomers

AgarAgar

AlginateAlginate

PolysulfidesPolysulfides

PolyethersPolyethers

Additionsilicone

Additionsilicone

Condensationsilicone

Condensationsilicone

Non-aqueouselastomers

Non-aqueouselastomers

PolyethersPolyethers

Additionsilicone

Additionsilicone

Condensationsilicone

Condensationsilicone

PolysulfidesPolysulfides

ElasticElastic

HydrocolloidsHydrocolloidsAgarAgar

AlginateAlginate

• High accuracy Biocompatibility

(very small contraction <0.5%)

• High dimensional stability Compatibility to stone• High elastic recovery High tear strength• Ease of use Long shelf life• Hydrophilic Pleasant color &taste

and Hydrophobic• Proper setting time Cost

(Ideal Properties) (Ideal Properties)

Impression plasterADA type I gypsum product

Impression plasterFor edentulous impression

Contraindication for undercut

CompositionCalcium sulfate hemihydrate (CaSO4)2.H20

Potassium sulfate Reduce expansion

Borax Reduce the rate of setting time

Starch Help disintegration of the impression from plaster model

Reaction

Calcium sulfate hemihydrate + water

calcium sulfate dihydrate

Mechanical propertiesVery low viscosity (mucostatic) HydrophilicGood dimension stability 0.06%Great accuracy

ManipulationEasy to mix, trapping air bubblesW/P ratio must be measured out carefullyUse in special tray, thickness of 1.0-1.5 mm.Setting time 2-3 minutesMust apply separating medium before pouring

the impressionPowder must be stored in air tight

AdvantageAccuracy to soft tissue impression

Good accuracyShort setting time

DisadvantageCan not be used in undercut ridge

Able to flow to pharyngesHeat due to reactionSensation of dryness

Impression compound

Type I Type II

Impression compound Green stick compound

Impression with compound

Type I

Type II

CompositionNatural resin 40%Waxes 7%Stearic acid 3%Filler&inorganic pigment 50%

RESINSAmorphous organic substance which

are insoluble in waterMake ThermoplasticShellac, dammar, rosin or sandarac

WAXESStraight chain hydrocarbon

CH3(CH2)nCH3

Tasteless, Odorless, ColorlessMake Thermoplasticbeeswax and colophany

Stearic acid

FillersControl degree of flowMinimize shrinkageImprove rigidityDiatomaceous earth, Soapstone, talc

•Lubricant and Plasticizer

Mechanical properties

High viscosity

High contraction coefficients 0.3%

Very low thermal conductivity

Reversible physical process

Thermoplastic 37-45 C๐

High thermal expansion

ManipulationSoften by heating over the flame or water bathDo not heat too much volatileTake impressionRoom temperature water coolingPour impression as soon as possibleWarm the impression before take the cast

Water bathAlcohol lampAlcohol torch

Advantage

Compatible with model material

Can take impression again

Disadvantage

Must be poured within one hour

Mucocompressive

=> dimensional change

Very technique sensitive

High coefficient of thermal expansion

Low detail reproduction

TroubleshootingDistortion

-Material is not completely cooled

-Flexible tray

-Delay in pouring

TroubleshootingCompound is too brittle or grainy

-Prolong immersion in the water bath

Zinc oxide-eugenol Impression paste

Zinc oxide-eugenol Impression paste

Zinc oxide-eugenolFor full arch edentulous impression without or minor

undercut

Bite registration

Wash impression

Temporary cementation Temporary filling

Composition (base)Zinc oxide (ZnO)OilHydrogenated rosinZinc acetate AcceleratorTrace of water Initiator

Composition (reactor)Eugenol 12~15%OilRosinFiller (kaolin)

Non eugenol paste Carboxylic acids

Reaction

ZnO + eugenol Zn eugenolate + ZnO(unreacted)

(powder) (liquid)

(Solid)

Mechanical properties@ Very low viscosity

@ Low dimensional change@ Low dimensional change 0.1%0.1%

@ Irreversible chemical change@ Irreversible chemical change

Manipulation

Manipulation Equal length of the two paste is extruded

shorten by increase

Temperature&HumidityTemperature&Humidity

Working time 3-5 min

Mixing time 45-60 s

Mixed with stainless steel spatula in paper

pad or glass slab

AdvantageAccuracy of soft tissue impression (mucostatic)

Inexpensive Adhere well to dental compound

Good surface detail reproduction

Good dimensional stability

Disadvantage MessinessNon elastic TimeUnstable setting May irritating to soft tissue

TroubleshootingInadequate working or setting time

-excessive humidity and/or temperature

Distortion

-unstable tray

Impression waxKORECTA WAX , IOWA WAX

Manipulation Functional Impression

Disinfection of Impression Materials Irreversible Hydrocolloids (Alginate)

Diagnostic Casts: Soak 10 min in Gluteraldehyde

Final Impressions:

Dip in Gluteraldehyde ,rinse in sterile water, dip again let stand under damp gauze 10 min Spray with Sodium Hypochlorite rinse, spray again & let stand under damp gauze 10 min

Reversible Hydrocolloid Dip in Gluteraldehyde ,rinse in sterile water, dip again let stand under damp gauze 10 min Spray with Sodium Hypochlorite rinse, spray again & let stand under damp gauze 10 min

Addition –reaction Silicones

In Gluteraldehyde 1 hr., Rinse sterile water Soak in fresh solution Gluteraldehyde 10 min

Zinc oxide eugenol Soak in Gluteraldehyde 10 min

Silicone Impressions Soak for 10 min Gluteraldehyde

Polyether Impressions Dip in Gluteraldehyde ,rinse in sterile water, dip again let stand under damp gauze 10 min

Fundamentals of Removable Partial Dentures 2nd Ed. CP Owen

REFERENCESREFERENCES

•Skinner’s Science of Dental Materials

•Dental Materials and Their Selection (William J. O’Brien)

•Introduction to dental materials (Richard Van Noort)

•Dr Sukontip Arwatchanakan

•Science of Dental Materials Phillips 11th Ed.

•Stephen C. Bayne Department of Operative Dentistry School of DentistryUniversity of North Carolina

•Mr. Robert Seghi Alginate Impression Materials (alginate lecture 2006.ppt)

Tray Selection CriteriaFeel comfortable to the patient. Extends slightly beyond the facial surfaces of the

teeth. Extends approximately 2 to 3 mm beyond the third

molar, retromolar, or tuberosity area of the arch. Is sufficiently deep to allow 2 to 3 mm of material

between the tray and incisal or occlusal edges of the teeth.

Characteristics of Impression TraysQuadrant tray

Covers one half of the arch. Section tray

Covers the anterior portion of the arch. Full arch tray

Covers the entire arch.Perforated tray

Holes in the tray create a mechanical lock to hold the material in place.

Smooth trayInterior of the tray is painted or sprayed with an

adhesive to hold the impression material.

Impression TraysMust be sufficiently rigid to:

Carry the impression material into the oral cavity.Hold the material in close proximity to the teeth.Avoid breaking during removal.Prevent warping of the completed impression.

Tray Adhesives VPS adhesives (blue)

For polyvinyl siloxane and polyether impression materials.

Rubber Base Adhesive (brown) Used with rubber base impression materials.

Silicone Adhesive (orangish-pink)Used with silicone impression materials.

Characteristics or Elastomeric Impression MaterialsBase

Packaged as a paste in a tube, as a cartridge, or as putty in a jar.

CatalystAlso known as the accelerator, is packaged as a

paste in a tube, as a cartridge, or as a liquid in a bottle with a dropper top.

Forms of Elastomeric Materials Light-bodied

Also referred to as syringe type, or wash type. This material is used because of its ability to flow in and about the details of the prepared tooth. A special syringe, or extruder, is used to place the light-bodied material on and immediately around the prepared teeth.

Forms of Elastomeric Materials cont’d Regular and heavy-bodied

Often referred to as tray‑type materials, they are much thicker. As the names imply, they are used to fill the tray. Their stiffness helps to force the light‑bodied material into close contact with the prepared teeth and surrounding tissues to ensure a more accurate impression of the details of a preparation.

Basic Impression Technique1. The material selected depends upon the dentist’s preference

and the type of impression required for the procedure.2. The dentist prepares the tooth or teeth for the impression. 3. The light-bodied material is prepared and loaded into the

syringe and transferred to the dentist.4. The dentist places the light-bodied material over and around

the prepared teeth and onto the surrounding tissues.5. The heavy-bodied material is prepared and loaded into the

tray and transferred to the dentist.6. When the impression material has reached final set, the

impression is removed and inspected for accuracy.7. The impression is disinfected, placed in a biohazard bag,

labeled, and readied for the laboratory technician.

Curing Stages of Elastomeric Materials Initial set

The first stage results in stiffening of the paste without the appearance of elastic properties. The material may be manipulated only during this first stage.

Final set The second stage begins with the appearance of

elasticity and proceeds through a gradual change to a solid rubberlike mass. The material must be in place in the mouth before the elastic properties of the final set begin to develop.

Final cure The last stage occurs from 1 to 24 hours.

Types of Elastomeric Materials

PolysulfidePolyetherSiliconePolyvinyl siloxane

Occlusal Registration An accurate registration of the normal centric

relationship of the maxillary and mandibular arches. Also commonly referred to as the bite registration.

Types of Occlusal Registration

Wax biteUseful when the diagnostic casts are trimmed.The most common technique is to use a softened

baseplate wax.

Types of Occlusal Registration cont’dPolysiloxane bite registration paste: Supplied

both as a paste system and also as cartridges.The material is fast setting.There is no resistance to biting forces.There is no odor or taste for the patient.It gains dimensional stability over time.It is convenient to use.

Types of Occlusal Registration cont’dZinc oxide-eugenol (ZOE) bite registration paste

ZOE paste has little to no resistance to bite closure and is a fast-setting material.

Material is supplied in a paste system and dispensed onto a paper pad, mixed, and placed onto a gauze tray for the patient to bite into.