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Dental impression materials Dental impression materials Libyan International Medical University Libyan International Medical University

Dental impression materials

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Dental impression materials. Libyan International Medical University. Introduction, types, classification. What is a dental impression?. It’s a negative likeness of the teeth and/or other tissues of the oral cavity. - PowerPoint PPT Presentation

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Page 1: Dental impression materials

Dental impression materialsDental impression materials

Libyan International Medical UniversityLibyan International Medical University

Page 2: Dental impression materials

04/20/23 2

Introduction, types, classification

Page 3: Dental impression materials

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What is a dental impression?What is a dental impression?

It’s a negative likeness of the teeth and/or other It’s a negative likeness of the teeth and/or other tissues of the oral cavity.tissues of the oral cavity.

The impression materials must be in a plastic or fluid The impression materials must be in a plastic or fluid status which become hard or set while in contact status which become hard or set while in contact with oral tissues.with oral tissues.

Impression tray is a device used to carry and control Impression tray is a device used to carry and control impression material while making an impression.impression material while making an impression.

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Ideal requirements of impression Ideal requirements of impression materialsmaterials

1.1. Biocompatible, non toxic and non irritant.Biocompatible, non toxic and non irritant.

2.2. Should have acceptable taste, colour and smell.Should have acceptable taste, colour and smell.

3.3. Adequate shelf life for storage.Adequate shelf life for storage.

4.4. Easy to manipulate.Easy to manipulate.

5.5. Suitable working and setting time.Suitable working and setting time.

6.6. Should be elastic to allow removal from undercuts Should be elastic to allow removal from undercuts without permanent deformation.without permanent deformation.

7. 7. Adequate strength so that will not tear or break on Adequate strength so that will not tear or break on removal from the mouth.removal from the mouth.

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8. Should give accurate reproduction of tissue details.8. Should give accurate reproduction of tissue details.

9. Compatible with cast or die materials.9. Compatible with cast or die materials.

10. Adhere to the impression tray.10. Adhere to the impression tray.

11. Should have good flow.11. Should have good flow.

12. Dimensionally stable.12. Dimensionally stable.

13. Can be disinfected without any changes of 13. Can be disinfected without any changes of properties.properties.

14. Economic or not expensive. 14. Economic or not expensive.

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Classification of impression materialsClassification of impression materials

• Non-elasticNon-elastic

imp. Compound, imp. Plaster, zinc oxide imp. Compound, imp. Plaster, zinc oxide eugenol and imp. Wax.eugenol and imp. Wax.

Must not have undercutsMust not have undercuts

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2. Elastic……can be used in undercut2. Elastic……can be used in undercut

a.a. HydrocolloidsHydrocolloids

Reversible (agar)……sol.Reversible (agar)……sol.↔ gel (temp)↔ gel (temp)

Irreversible (alginate)…..sol.Irreversible (alginate)…..sol.→ gel→ gel

b. b. ElastomersElastomers

Polysulfide (PS)............Polysulfide (PS)............set by polymerizationset by polymerization

Silicon rubber (AS and CS)Silicon rubber (AS and CS)

Polyethers (PE)Polyethers (PE)

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Impression techniquesImpression techniques

• Full denturesFull dentures

• Partial denturesPartial dentures

• Fixed prosthodonticsFixed prosthodontics

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What's important?What's important?

PatientPatient

• Neutral taste and odourNeutral taste and odour

• Short setting timeShort setting time

• Small traySmall tray

• Easily removedEasily removed

• No retakesNo retakes

• Non-toxicNon-toxic

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What's important?What's important?

DentistsDentists

• Easily mixedEasily mixed

• Short working timeShort working time

• Good quality impressionGood quality impression

• Low costLow cost

• Easily disinfectedEasily disinfected

• Simple procedureSimple procedure

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Ease of mixingEase of mixing

Low viscosity Low viscosity

less viscous is easierless viscous is easier

silicones are easiest to mix followed by silicones are easiest to mix followed by polyether and polysulphidespolyether and polysulphides

Automatic mixingAutomatic mixing

reduces mixing time and bubblesreduces mixing time and bubbles

use correct mixing tipuse correct mixing tip

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Auto-mixer

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Working and setting timeWorking and setting time

Dentist's time requirements must be balanced with Dentist's time requirements must be balanced with patient's comfort.patient's comfort.

A total working and setting time of 4 min is A total working and setting time of 4 min is adequate for most crown and bridge procedures.adequate for most crown and bridge procedures.

Using auto-mixing device for direct injection Using auto-mixing device for direct injection reduce working time to one minute.reduce working time to one minute.

A fast setting material can be removed from the A fast setting material can be removed from the mouth in about 3 min.mouth in about 3 min.

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Working and setting timeWorking and setting time

0

1

2

3

4

5

6

7

8

Ideal HAS AS CS PE PS

Tot

al ti

me

(min

)

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Easy of removalEasy of removal

Flexible.Flexible.

depends on the elastic modulusdepends on the elastic modulus Minimal distortion.Minimal distortion.

depends on degree of permanent deformation.depends on degree of permanent deformation. Sufficient tear strength.Sufficient tear strength.

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Flexibility of Impression materialsFlexibility of Impression materials

0

1

2

3

4

5

6

Ideal HAS AS CS PE PS

Hard

Moderate

Easy

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Resistance to TearingResistance to Tearing

0

1

2

3

4

5

6

Ideal HAS AS CS PE PS

High

Medium

Low

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Accurate reproduction of surface Accurate reproduction of surface detailsdetails

ViscosityViscosity

High- muco-compressiveHigh- muco-compressive

Low- muco-staticLow- muco-static Wettability…..ability of liquid to cover the Wettability…..ability of liquid to cover the

surface of the substrate completelysurface of the substrate completely

HydrophobicHydrophobic

HydrophilicHydrophilic

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Why do we want good wetting?Why do we want good wetting?

1.1. Fewer voidsFewer voids

2.2. Less entrapment of oral fluidsLess entrapment of oral fluids

3.3. Bubble-free dies and modelsBubble-free dies and models

4.4. Fewer retakesFewer retakes

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Wettability of Impression materialsWettability of Impression materials

0

1

2

3

4

5

6

Ideal HAS AS CS PE PS

Fair

Good

Excellent

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Wettability of Impression materialsWettability of Impression materials

• Displace water and other oral fluids from Displace water and other oral fluids from the surfaces in the mouth so as to prevent the surfaces in the mouth so as to prevent voids in the impression and consequent voids in the impression and consequent bubbles in the casts.bubbles in the casts.

• Improve adaptation of gypsum so as to Improve adaptation of gypsum so as to prevent voids in the casts.prevent voids in the casts.

• Disinfection procedure! Disinfection procedure!

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Dimensional accuracy and stabilityDimensional accuracy and stability

• Choice and use of trayChoice and use of tray

• Setting shrinkageSetting shrinkage

• Permanent setPermanent set

• Storage stabilityStorage stability

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Choice and use of traysChoice and use of trays

• Avoid flexible traysAvoid flexible trays• Use perforated traysUse perforated trays• Make sure the trays is cleanMake sure the trays is clean• Apply only a thin layer of adhesiveApply only a thin layer of adhesive• Wait appropriate time before taking Wait appropriate time before taking

impressionimpression• Do not mix adhesives and impression Do not mix adhesives and impression

materialsmaterials

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Dimensional change of impressionsDimensional change of impressions

0

1

2

3

4

Ideal HAS AS CS PE PS

Low

Medium

High

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Oversized impression space results in an oversized die

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a. Elastic material, b. plastic material, c. viscoelastic material

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a. Impression in place before removal, b. during removal- the impression is subjected to both compressive and tensile stresses.

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View of a material being used to record an impression of a crown with subgingival shoulders. The thin areas of impression material, which are most prone to fracture are arrowed.

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Imp wax

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Impression plasterImpression plaster

• Rarely used these days as they are brittle Rarely used these days as they are brittle and fractures very easily.and fractures very easily.

• Mucostatic impression of edentulous ridgesMucostatic impression of edentulous ridges

• High W/P ratioHigh W/P ratio

• Can be combined with impression Can be combined with impression compoundcompound

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Impression plasterImpression plaster

Easy to mixEasy to mix Working time 2-3 minWorking time 2-3 min Setting time 2-3 minSetting time 2-3 min Low viscosity-mucostaticLow viscosity-mucostatic Good dimensional stability and accuracyGood dimensional stability and accuracy CheapCheap

advantages

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• Low strengthLow strength

• Rough surface finishRough surface finish

• Poor abrasion resistancePoor abrasion resistance

• Rigid once setRigid once set

• Dry sensation in the mouthDry sensation in the mouth

• We need separatorWe need separator

Disadvantages

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Impression compoundImpression compound

SheetSheet

primary impression of edentulous mouth.primary impression of edentulous mouth.

close fitting special tray used with zinc oxide close fitting special tray used with zinc oxide eugenol wash.eugenol wash.

StickStick

single crown impression (copper ring technique).single crown impression (copper ring technique).

Border molding.Border molding.

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Composition Composition

• Thermoplastic materials, natural or Thermoplastic materials, natural or synthetic resin and waxes….47% synthetic resin and waxes….47% characterizes the softening temp.characterizes the softening temp.

• Fillers…..e.g. Talc or shalk 50%..gives Fillers…..e.g. Talc or shalk 50%..gives body increasing viscosity of the softened body increasing viscosity of the softened materials, reduce thermal contraction.materials, reduce thermal contraction.

• Lubricant or acids 3% e.g. stearic acid to Lubricant or acids 3% e.g. stearic acid to improve flow properties (plasticizer).improve flow properties (plasticizer).

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PropertiesProperties• Softening temperature 55-60Softening temperature 55-60ºC….↑ flow by Temp.ºC….↑ flow by Temp.

• High viscosity-mucocompressive…37ºC solid.High viscosity-mucocompressive…37ºC solid.• High coefficient of thermal expansion….High coefficient of thermal expansion….• Do not over heat because it loose oils and altered Do not over heat because it loose oils and altered

characteristicscharacteristics

• Rigid….↑ with rigid trayRigid….↑ with rigid tray

• Poor thermal conductivity….take time during heating or Poor thermal conductivity….take time during heating or cooling.cooling.

• Poured as soon as possiblePoured as soon as possible

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• Since pressure is applied during the Since pressure is applied during the formation of the impression, the residual formation of the impression, the residual stress occurs in the material storage in stress occurs in the material storage in warm environments or extended storage warm environments or extended storage results in warpage.results in warpage.

• Contraction of imp. Compound from oral Contraction of imp. Compound from oral temp. to room temp. is 0.3%temp. to room temp. is 0.3%

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Zinc oxide eugenolZinc oxide eugenol• Mucostatic impression of edentulous ridge.Mucostatic impression of edentulous ridge.• Initial ST 3-6 min.Initial ST 3-6 min.• Final ST 10 min.Final ST 10 min.• Two pastes, different colors, equal length, different size Two pastes, different colors, equal length, different size

opening….opening….• Not elastic.Not elastic.• Temp. and moisture Temp. and moisture ↓ ST….accelerate reaction…drop of water ↓ ST….accelerate reaction…drop of water

accelerate setting. accelerate setting. • Stick to dry surfaces.Stick to dry surfaces.• Eugenol irritant, cause burning sensation of lips.Eugenol irritant, cause burning sensation of lips.• Pour any time.Pour any time.

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• No separator needs.No separator needs.

• Protect unsupported edges.Protect unsupported edges.

• Put Vaseline on patient lips.Put Vaseline on patient lips.

• If patient irritant to eugenol use rubbers imp. or If patient irritant to eugenol use rubbers imp. or eugenol free (phenols) zinc oxide impression.eugenol free (phenols) zinc oxide impression.

• MucostaticMucostatic

• Hydrophilic….accurate reproduction of surface detailsHydrophilic….accurate reproduction of surface details

• Dimensionally stable…. 0.1%Dimensionally stable…. 0.1%

• Compatible with dental stone….separated by softening Compatible with dental stone….separated by softening the set paste in water at 60the set paste in water at 60ºC.ºC.

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• Eugenol react with zinc-oxide to form salt of Eugenol react with zinc-oxide to form salt of zinc eugenolate and unreacted zinc oxide.zinc eugenolate and unreacted zinc oxide.

• Normally used with close-fitting special tray.Normally used with close-fitting special tray.

• The thickness of paste used is normally around 1 The thickness of paste used is normally around 1 mm.mm.

• This thin section This thin section ↓ the dimensional changes.↓ the dimensional changes.

• Low viscosity of the mixed paste gives accurate Low viscosity of the mixed paste gives accurate recorded details.recorded details.

• Defect sometimes arise on the surface of the Defect sometimes arise on the surface of the impression but can be corrected by imp. Wax.impression but can be corrected by imp. Wax.

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• The major restriction is their lack of The major restriction is their lack of elasticity.elasticity.

• The set material easily distort or fracture The set material easily distort or fracture when removed from undercut.when removed from undercut.

• Available in two types identified as hard set Available in two types identified as hard set and soft set.and soft set.

• The mixed materials has adequate adhesion The mixed materials has adequate adhesion to acrylic or tray material, therefore to acrylic or tray material, therefore adhesives do not need. adhesives do not need.

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HydrocolloidsHydrocolloids

• Hydro=water kola=glue Oid=likeHydro=water kola=glue Oid=like

• A solution is a homogenous mixture A solution is a homogenous mixture consisting of single phase.consisting of single phase.

• A suspension is a mixture of two phasesA suspension is a mixture of two phases

• A colloid is a heterogeneous mixture of two A colloid is a heterogeneous mixture of two phases, where the two phases are not easily phases, where the two phases are not easily differentiated.differentiated.

• Agar and alginate impression materials.Agar and alginate impression materials.

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• Reversible hydrocolloids …..agarReversible hydrocolloids …..agar

Gel Gel → Sol → Gel → Sol → Gel

Irreversible hydrocolloids…..alginateIrreversible hydrocolloids…..alginate

Sol → Gel Sol → Gel

heating cooling

Chemical reaction

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AgarAgar• Sea weedSea weed

• Uses…..crown/bridge imp, cast duplicate-lab.Uses…..crown/bridge imp, cast duplicate-lab.

• Composition; Agar 15%, Borax .2%, sodium Composition; Agar 15%, Borax .2%, sodium sulphate 1%, anti fungal and water 85%sulphate 1%, anti fungal and water 85%

• Good storageGood storage

• Strengthens gelStrengthens gel

• Affect gypsum setting against? Why!!!Affect gypsum setting against? Why!!!

• Accurate detailsAccurate details

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• Largely replaced by alginate and rubber Largely replaced by alginate and rubber impression materials.impression materials.

• The preference of alginate as result of The preference of alginate as result of minimum equipment required and rubber minimum equipment required and rubber imp due to greater dimensional stability, imp due to greater dimensional stability, high quality gypsum model and option of high quality gypsum model and option of obtain metal or epoxy die.obtain metal or epoxy die.

• It supplies as a gel in tooth paste like tube It supplies as a gel in tooth paste like tube or syringe. or syringe.

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• Manipulation:Manipulation:

Agar is normally conditioned before use, using Agar is normally conditioned before use, using a specially designed conditioned bath.a specially designed conditioned bath.

This consists of three rooms each contain water.This consists of three rooms each contain water.

The tube or syringe of gel is first placed in the The tube or syringe of gel is first placed in the 100100ºC bath. This rapidly convert gel to sol ºC bath. This rapidly convert gel to sol and content of tube become very fluid (10 and content of tube become very fluid (10 min).min).

The tube then transferred to the 65ºC bath The tube then transferred to the 65ºC bath where it is stored until required for use.where it is stored until required for use.

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• A few minutes before the impression is A few minutes before the impression is recorded, the contents are cooled to 45recorded, the contents are cooled to 45ºC, ºC, prevent burn and pulp death.prevent burn and pulp death.

• If the material is maintained in If the material is maintained in 4545ºC for long, it ºC for long, it slowly convert to gel.slowly convert to gel.

• The conversion from sol to gel takes place The conversion from sol to gel takes place slowly (many minutes) at mouth temp and it slowly (many minutes) at mouth temp and it could be accelerator by cooled water spray onto could be accelerator by cooled water spray onto the imp tray or by using water-cooled imp tray.the imp tray or by using water-cooled imp tray.

• Agar is very sensitive to water uptake and loss Agar is very sensitive to water uptake and loss (syneresis and imbibition).(syneresis and imbibition).

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Water bath used for conditioned agar imp material

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• After recording an imp it should be poured within After recording an imp it should be poured within 30 minutes.30 minutes.

• Short storage, wet tissue in sealed bag.Short storage, wet tissue in sealed bag.

• Its possible to re-use agar, however, concerns a Its possible to re-use agar, however, concerns a about cross infection, alteration of material about cross infection, alteration of material properties and incorporation of small gypsum properties and incorporation of small gypsum chips.chips.

• Expensive instruments.Expensive instruments.

• hydrophilichydrophilic

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AlginateAlginate

• Widely used? Diagnostic casts, primary Widely used? Diagnostic casts, primary impression for CD, PD, opposing jaw for impression for CD, PD, opposing jaw for CC&B, repairs of prosthesis, provisional &B, repairs of prosthesis, provisional restorations, flouride and bleaching trays, restorations, flouride and bleaching trays, night guards, sport protector.night guards, sport protector.

• Not fine details and low flow.Not fine details and low flow.

• Not CNot C&B, inlays, onlays…..&B, inlays, onlays…..

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Advantages of alginate over other Advantages of alginate over other impression materialsimpression materials

1.1. Ease of mixing and manipulationEase of mixing and manipulation

2.2. Minimum equipmentMinimum equipment

3.3. Flexibility of the set impression materialFlexibility of the set impression material

4.4. Accuracy if properly handledAccuracy if properly handled

5.5. Cost effectivenessCost effectiveness

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DisadvantagesDisadvantages

1.1. They restrict the choice of model and die They restrict the choice of model and die materials…we can not make a metal die materials…we can not make a metal die which have higher abrasion resistance.which have higher abrasion resistance.

2.2. They do not give fine details to gypsum They do not give fine details to gypsum die as Agar or rubber impression do.die as Agar or rubber impression do.

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• P sulphateP sulphate

• Tri Na phosphate retarderTri Na phosphate retarder

• Glycols for dustless algGlycols for dustless alg

• Colour, disinfectants, flavour, fillerColour, disinfectants, flavour, filler

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CompositionComposition• Sodium or potassium salt……..to dissolve in water.Sodium or potassium salt……..to dissolve in water.• Calcium sulfate……to react with dissolved alginate to Calcium sulfate……to react with dissolved alginate to

form insoluble calcium alginate.form insoluble calcium alginate.• Sodium phosphate……react with calcium sulfate and Sodium phosphate……react with calcium sulfate and

act as retarderact as retarder• Silicate powder……to control the consistency of mix Silicate powder……to control the consistency of mix

and flexibility of the impression.and flexibility of the impression.• Potassium sulfate or potassium fluoride….to counteract Potassium sulfate or potassium fluoride….to counteract

the inhibiting effect of alginate on gypsum model or die.the inhibiting effect of alginate on gypsum model or die.

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• Organic Glycol…..to coat the powder Organic Glycol…..to coat the powder particles to minimize dust during particles to minimize dust during dispensing.dispensing.

• Chlorhexidine…..to provide self Chlorhexidine…..to provide self disinfection.disinfection.

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ManipulationManipulation• When water and powder are mixed, a smooth When water and powder are mixed, a smooth

plastic mass is formed which become an plastic mass is formed which become an irreversible gel a few minutes after mixing.irreversible gel a few minutes after mixing.

• Sodium alginate+CaSOSodium alginate+CaSO44+H+H22O O → Calcium → Calcium

alginate+Na+SOalginate+Na+SO44+H+H22O.O.

• The manufacturer controls the setting time by The manufacturer controls the setting time by amount of sodium phosphate in the powder.amount of sodium phosphate in the powder.

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ManipulationManipulation

• Powder and water-dispensing cup.Powder and water-dispensing cup.

• Rubber mixing bowlRubber mixing bowl

• Spatula with a reasonably wide and flexible Spatula with a reasonably wide and flexible bladeblade

• Proper size of tray should be selected before Proper size of tray should be selected before the mixing is begunthe mixing is begun

• Perforated or rim locks trayPerforated or rim locks tray

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PropertiesProperties

1.1. Mixing and setting timesMixing and setting times…….smooth, …….smooth, creamy creamy consistency and free of graininess in less than 1 min.consistency and free of graininess in less than 1 min.

Normal set usually set in 2 minutes that is about 4 Normal set usually set in 2 minutes that is about 4 minutes after the start of initial mix.minutes after the start of initial mix.

There are normal and fast set alginateThere are normal and fast set alginate Increase water Temp will increase the speed of Increase water Temp will increase the speed of

reaction and decrease the WT and ST. reaction and decrease the WT and ST. Proportion of powder and water also affects the Proportion of powder and water also affects the

setting timesetting time

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2. Permanent deformation2. Permanent deformation

• Most of commercially available alginate Most of commercially available alginate have about 1.5% permanent deformation.have about 1.5% permanent deformation.

• Alginate is flexible but not perfectly elastic.Alginate is flexible but not perfectly elastic.

• The amount of plastic deformation The amount of plastic deformation increased when the time that it is held under increased when the time that it is held under compression is increased and W/P ratio is compression is increased and W/P ratio is increased.increased.

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3. Strength3. Strength

• The strength of alginate in compression and The strength of alginate in compression and tearing are important, the tear strength is more tearing are important, the tear strength is more critical.critical.

• Higher rates of removal (deformation) resulting in Higher rates of removal (deformation) resulting in higher compressive and tear strengths.higher compressive and tear strengths.

• The strength of alginate The strength of alginate ↑ when mix is thick than ↑ when mix is thick than thin.thin.

• The tear and compressive strength increased if the The tear and compressive strength increased if the time of removal is delayed.time of removal is delayed.

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4. Dimensional change4. Dimensional change

• Set alginate contain large quantities of Set alginate contain large quantities of water. It loses water and shrinks if stored in water. It loses water and shrinks if stored in air and absorbs water and expands if stored air and absorbs water and expands if stored in water.in water.

• Storage in 100% humidity results in the Storage in 100% humidity results in the least dimensional changes (least dimensional changes (maximum one maximum one hour)hour)..

• Syneresis and Syneresis and imbibition.imbibition.

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5. Disinfection5. Disinfection

• Sodium hypochlorite (10 min), iodophor Sodium hypochlorite (10 min), iodophor (10 min), glutaraldehyde and phenylphenol (10 min), glutaraldehyde and phenylphenol (20 min) solutions has been used and some (20 min) solutions has been used and some manufacturers have added disinfectant to manufacturers have added disinfectant to the alginate powder.the alginate powder.

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• After removing the impression from pt After removing the impression from pt mouth should be rinsed with water to mouth should be rinsed with water to remove ay blood and saliva……why?remove ay blood and saliva……why?

• Agar-alginate impression…..agar is injected Agar-alginate impression…..agar is injected around the prepared tooth or teeth, then tray around the prepared tooth or teeth, then tray contains alginate mix is placed over agar contains alginate mix is placed over agar before it get jelly.before it get jelly.

• This technique elements the use of water This technique elements the use of water cooled impression trays!cooled impression trays!

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AlginateAlginate• Dust free powderDust free powder• CheapCheap• Limited shelf lifeLimited shelf life• Well controlled working and setting timeWell controlled working and setting time• MucostaticMucostatic• HydrophilicHydrophilic• Poor surface reproductionPoor surface reproduction• Poor storage stability…Imbibition and syneresisPoor storage stability…Imbibition and syneresis• Low tear strengthLow tear strength• Permanent deformationPermanent deformation

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Elastomeric impression materialsElastomeric impression materials

• PolysulphidesPolysulphides

• PolyethersPolyethers

• SiliconesSilicones

condensation curedcondensation cured

addition cured addition cured

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Polysulfide rubber impression materialPolysulfide rubber impression material

• The first rubber based impression material The first rubber based impression material was a polysulfide.was a polysulfide.

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• Classification and Uses: Classification and Uses: ••. Supplied as a two paste system one tube labeled . Supplied as a two paste system one tube labeled

Catalyst or Accelerator and the other marked Base Catalyst or Accelerator and the other marked Base . .

••. They are classified into three as:- Light, Regular, . They are classified into three as:- Light, Regular, or Heavy-bodied depending on their viscosity and or Heavy-bodied depending on their viscosity and how easily they flow under load. how easily they flow under load.

.•. The light bodied class is used as a syringe .•. The light bodied class is used as a syringe material in combination with a tray material, and material in combination with a tray material, and the regular material is used alone. The light the regular material is used alone. The light material is also used alone in case of a custom-material is also used alone in case of a custom-made tray (special tray) for the preparation of made tray (special tray) for the preparation of dentures. dentures.

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Composition Composition • Base:Base: ••. 80% low-molecular weight organic polymer, containing . 80% low-molecular weight organic polymer, containing

reactive Mercaptan (-SH) groups, and 20% reinforcing reactive Mercaptan (-SH) groups, and 20% reinforcing agents, such as Titanium Dioxide, Zinc Sulfate, Copper agents, such as Titanium Dioxide, Zinc Sulfate, Copper Carbonate, or Silica. Carbonate, or Silica.

• Accelerator/Catalyst:Accelerator/Catalyst: ••. This tube contains a compound that causes the Mercaptan . This tube contains a compound that causes the Mercaptan

groups to react to form a Poly sulfide Rubber. groups to react to form a Poly sulfide Rubber. An inert oil such as Dibutyl or Dioctyl Phthalate carries the An inert oil such as Dibutyl or Dioctyl Phthalate carries the

catalyst. catalyst. • • The catalyst is Lead Dioxide, with or without Manganese The catalyst is Lead Dioxide, with or without Manganese

Dioxide; using it results in the paste, being dark brown to Dioxide; using it results in the paste, being dark brown to gray. gray.

Another catalyst system is Copper hydroxide and when Another catalyst system is Copper hydroxide and when mixed with the white base paste a blue green color results. mixed with the white base paste a blue green color results.

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Setting Reaction Setting Reaction

• The overall setting reaction involves the Oxidation The overall setting reaction involves the Oxidation of the Mercaptan groups from two different of the Mercaptan groups from two different molecules in the presence of the catalyst that joins molecules in the presence of the catalyst that joins the molecules together, forming Disulphide bonds. the molecules together, forming Disulphide bonds.

• Mercaptan Mercaptan + + Lead Oxide Polysulfide Lead Oxide Polysulfide + + H20 H20 • The reaction is very sensitive to moisture and The reaction is very sensitive to moisture and

temperature and increase in either of these would temperature and increase in either of these would lead to an acceleration in the setting reaction lead to an acceleration in the setting reaction

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Properties of clinical interest are: Properties of clinical interest are:

• Toxicity Toxicity • Color of the base and accelerator Color of the base and accelerator • Time required for mixing Time required for mixing • Working time Working time • Consistency Consistency • Permanent deformation during removal Permanent deformation during removal • Dimensional stability Dimensional stability • Flow after setting Flow after setting • Flexibility Flexibility • Reproduction of detail Reproduction of detail • Compatibility with die and model materials Compatibility with die and model materials • Deterioration during storage of unmixed material Deterioration during storage of unmixed material

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• Although most accelerator pastes contains Lead Dioxide, Although most accelerator pastes contains Lead Dioxide, proper use does not result in any toxicity. proper use does not result in any toxicity.

• Manufacturer supplies the base paste as white in color and Manufacturer supplies the base paste as white in color and the other as in a contrasting color. When properly mixed the other as in a contrasting color. When properly mixed the mix is free of steaks and this can be done in about the mix is free of steaks and this can be done in about 45secs or no less than I min should be required. 45secs or no less than I min should be required.

• In general, the working time for poly sulfide rubber In general, the working time for poly sulfide rubber impression materials decreases as the consistency becomes impression materials decreases as the consistency becomes stiffer (from light -to heavy -bodied). The working time is stiffer (from light -to heavy -bodied). The working time is an indication of the maximum time allowed before the an indication of the maximum time allowed before the impression material should be in the mouth, with typical impression material should be in the mouth, with typical values being 5 to 7 mins. The final setting time is usually values being 5 to 7 mins. The final setting time is usually in the range of 8 to 12 minutes form the start of mixing. in the range of 8 to 12 minutes form the start of mixing.

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• The permanent deformation values, indicate that The permanent deformation values, indicate that polysulfides are not perfectly elastic and that compression polysulfides are not perfectly elastic and that compression during removal of the impressions should be kept to a during removal of the impressions should be kept to a minimum. The permanent deformation of polysulfide minimum. The permanent deformation of polysulfide rubber is slightly greater than that for Hydrocolloid rubber is slightly greater than that for Hydrocolloid Impression materials. Impression materials.

• Polysulfide rubber impression materials shrink 0.3% to.4% Polysulfide rubber impression materials shrink 0.3% to.4% during the first 24hrs and thus models and dies should be during the first 24hrs and thus models and dies should be prepared promptly. It is shown that the accuracy is slightly prepared promptly. It is shown that the accuracy is slightly increased if the models and dies are made in less than increased if the models and dies are made in less than 30mins. 30mins.

• The flexibility of polysulfides varies considerably with the The flexibility of polysulfides varies considerably with the heavy bodied materials having lower values. heavy bodied materials having lower values.

• Polysulfide rubber provides excellent reproduction of Polysulfide rubber provides excellent reproduction of surface detail and is readily capable of reproducing fine surface detail and is readily capable of reproducing fine lines 0.025mm wide. lines 0.025mm wide.

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• The polysuifides are highly compatible with model plaster The polysuifides are highly compatible with model plaster and high strength stones~ an impressions are easily and high strength stones~ an impressions are easily metallized by electroforming (electroplating). Silver metallized by electroforming (electroplating). Silver plating is easier than copper plating~ although their use plating is easier than copper plating~ although their use requires special care because of their poisonous nature. requires special care because of their poisonous nature.

• The polysulfide materials have excellent shelf life but The polysulfide materials have excellent shelf life but should not be stored in a warm location but is best if should not be stored in a warm location but is best if refrigerated. refrigerated.

• The resistance to tearing is about The resistance to tearing is about eight times eight times that reported that reported for Hydrocolloid impression materials. for Hydrocolloid impression materials.

• The strength of permanent deformation increases with time The strength of permanent deformation increases with time and a few extra minutes in the mouth will considerably and a few extra minutes in the mouth will considerably increase the characteristics. Also the time before the increase the characteristics. Also the time before the preparation of dies should be balanced as the continuation preparation of dies should be balanced as the continuation chemical reaction causes shrinkage. chemical reaction causes shrinkage.

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Manipulation:Manipulation:

• Two-Paste Type: Two-Paste Type:

• Equal lengths of the base and accelerator Equal lengths of the base and accelerator are extruded onto a paper pad. The are extruded onto a paper pad. The accelerator should not be extruded onto the accelerator should not be extruded onto the base as this may result in a non-base as this may result in a non-homogenous mix. A tapered stiff bladed homogenous mix. A tapered stiff bladed spatula is recommended. spatula is recommended.

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• If the material is a light-bodied, it is loaded into a If the material is a light-bodied, it is loaded into a syringe before injecting into the cavity syringe before injecting into the cavity preparation. preparation.

• If the material is a regular or heavy-bodied If the material is a regular or heavy-bodied material, it is placed in a tray. Custom made material, it is placed in a tray. Custom made acrylic trays may be constructed with a space of acrylic trays may be constructed with a space of 2mm for the impression material and a rubber 2mm for the impression material and a rubber cement adhesives should be painted. The adhesive cement adhesives should be painted. The adhesive should be allowed to evaporate as otherwise the should be allowed to evaporate as otherwise the Polysulfide material may separate from the tray Polysulfide material may separate from the tray during removal from the mouth. Sometimes holes during removal from the mouth. Sometimes holes can be drilled through the tray to provide can be drilled through the tray to provide mechanical retention. mechanical retention.

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• A variety of techniques are used to make A variety of techniques are used to make impressions. impressions.

• In case of light bodied materials the light bodied In case of light bodied materials the light bodied material is injected into the preparation and then material is injected into the preparation and then the heavy bodied material is placed in the tray and the heavy bodied material is placed in the tray and both the material sets together. both the material sets together.

• The same impression may also be accomplished The same impression may also be accomplished with a single mix of regular-bodied material. with a single mix of regular-bodied material.

• When the material is set it should be removed with When the material is set it should be removed with a steady force. If tearing of the impression occurs a steady force. If tearing of the impression occurs the second time the impression is left in the mouth the second time the impression is left in the mouth for a longer time to obtain higher tear strength. for a longer time to obtain higher tear strength.

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• After the removal of the impression it is After the removal of the impression it is checked for completeness and detail, checked for completeness and detail, thoroughly cleansed with water, disinfected thoroughly cleansed with water, disinfected and cleansed with water again. and cleansed with water again.

• The excess water is shaken off and moisture The excess water is shaken off and moisture removed by a gentle stream of air. removed by a gentle stream of air.

The next step is the preparation of the die or The next step is the preparation of the die or model and should not be delayed. model and should not be delayed.

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Silicone Rubber Impression Materials Silicone Rubber Impression Materials

• Disadvantages of Polysulfides as Compared to Disadvantages of Polysulfides as Compared to Silicones: Silicones:

• Objectionable odor. Objectionable odor. • Staining of uniforms by Lead Dioxide. Staining of uniforms by Lead Dioxide. • Amount of effort required to mix the base with the Amount of effort required to mix the base with the accelerator. accelerator. • Long setting times. Long setting times. • Moderately high shrinkage on setting. Moderately high shrinkage on setting. • Fairly high permanent deformation. Fairly high permanent deformation.

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CompositionComposition

• Classification: Classification:

• There are two types:There are two types:

• Condensation Silicones Condensation Silicones

• Addition Silicones Addition Silicones

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Condensation Silicones: Condensation Silicones: • Supplied as a base and Accelerator/Catalyst. Supplied as a base and Accelerator/Catalyst. • The base is a paste containing a moderately low molecular The base is a paste containing a moderately low molecular

weight Silicone liquid called a Dimethylsiloxane, which weight Silicone liquid called a Dimethylsiloxane, which has reactive -OH groups. has reactive -OH groups.

• Reinforcing agents such as Silica are added to give proper Reinforcing agents such as Silica are added to give proper consistency to the paste and stiffuess to the set rubber. consistency to the paste and stiffuess to the set rubber.

• The accelerator is usually supplied as a liquid but may be The accelerator is usually supplied as a liquid but may be provided as a paste by the use of thickening agents. provided as a paste by the use of thickening agents.

• The accelerator consists of a Tin Organic Ester suspension.The accelerator consists of a Tin Organic Ester suspension.• The silicone pastes are supplied in light, regular, and The silicone pastes are supplied in light, regular, and

heavy-bodied consistency as well as a very heavy heavy-bodied consistency as well as a very heavy consistency called a consistency called a Putty.Putty.

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• The consistency is controlled by the selection of The consistency is controlled by the selection of the molecular weight of the Dimethylsiloxane the molecular weight of the Dimethylsiloxane and the concentration of the reinforcing agent. and the concentration of the reinforcing agent. Higher molecular weights are used with the Higher molecular weights are used with the heavier bodied materials. heavier bodied materials.

• The concentration of reinforcing agents The concentration of reinforcing agents increases from 35% for light-bodied consistency increases from 35% for light-bodied consistency to 75% for the putty consistency. to 75% for the putty consistency.

• Ethyl Alcohol….by product of setting reaction.Ethyl Alcohol….by product of setting reaction.

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Setting Reaction: Setting Reaction: • The ethyl alcohol produced as a by-product in the The ethyl alcohol produced as a by-product in the

reaction gradually evaporates and contributes to reaction gradually evaporates and contributes to the high shrinkage during he first 24hrs after the high shrinkage during he first 24hrs after setting. setting.

• The incorporation of large amounts of filler in the The incorporation of large amounts of filler in the putty consistency results in a reduction of the putty consistency results in a reduction of the dimensional change. dimensional change.

• The setting reaction is sensitive to moisture and The setting reaction is sensitive to moisture and heat, with increases in either resulting in shorter heat, with increases in either resulting in shorter setting and working times. setting and working times.

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Addition Type Silicones: Addition Type Silicones:

• The material is supplied as a two-paste system or a two putty system, with one containing a low molecular weight Silicone having terminal Vinyl Groups, Reinforcing filler and the other containing a low molecular weight Silicone having Silane Hydrogens and reinforcing filler.

• The two are mixed in equal lengths of paste or equal quantities of putty, and the addition reaction occurs between the vinyl and hydrogen groups with no by product being formed.

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• No volatile by-product is formed in this reaction, and No volatile by-product is formed in this reaction, and minimal dimensional changes occur during minimal dimensional changes occur during polymerization.polymerization.

• Increases in temperature increase the rate of reaction and Increases in temperature increase the rate of reaction and

shorten the setting time. shorten the setting time.

• If the hydroxyl groups are present in the addition silicone, If the hydroxyl groups are present in the addition silicone, a side reaction occurs that results in the formation of a side reaction occurs that results in the formation of hydrogen. hydrogen.

• The hydrogen is gradually released from the set impression The hydrogen is gradually released from the set impression material and produces bubbles in gypsum dies prepared material and produces bubbles in gypsum dies prepared less than 1 hour or epoxy dies less than 24hrs, after the less than 1 hour or epoxy dies less than 24hrs, after the impression is made. impression is made.

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NoteNote• Some products permit the immediate pouring of Some products permit the immediate pouring of

dies by controlling the presence of Hydroxyl dies by controlling the presence of Hydroxyl Groups or by the inclusion in the impression Groups or by the inclusion in the impression material a hydrogen absorber such as Palladium. material a hydrogen absorber such as Palladium. Thus, the manufacturer's directions for the time of Thus, the manufacturer's directions for the time of preparation of die from a particular Silicone preparation of die from a particular Silicone should be followed. should be followed.

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• Properties: Properties: • Condensation types: Condensation types: • ~ It has moderate working time (6-8min). ~ It has moderate working time (6-8min). • ~ They have pleasant odor, a moderate high tear ~ They have pleasant odor, a moderate high tear

strength and excellent recovery from deformation; strength and excellent recovery from deformation; the permanent deformation is lower than that of the permanent deformation is lower than that of polysulphide. polysulphide.

• ~ Some of the materials are hydrophobic (makes ~ Some of the materials are hydrophobic (makes cast formation a problem). cast formation a problem).

• ~ Ideally it should be poured within one hour, ~ Ideally it should be poured within one hour, most of the dimensional changes occur during this most of the dimensional changes occur during this period. period.

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• Reproduce fine details. Reproduce fine details. • Non-toxic, allergic reactions have been noted. Non-toxic, allergic reactions have been noted. • Setting reaction is sensitive to moisture and heat. Setting reaction is sensitive to moisture and heat.

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• Addition Addition type: type: • The most accurate of the elastic impression materials. The most accurate of the elastic impression materials.

• They have less polymerization shrinkage, low distortion, They have less polymerization shrinkage, low distortion, fast recovery from deformation and a moderately high tear fast recovery from deformation and a moderately high tear strength. strength.

• It has a working time 3-5 min. It has a working time 3-5 min.

• They are available in both hydrophilic (adding surfactant) They are available in both hydrophilic (adding surfactant) & hydrophobic forms; have no smell or taste . & hydrophobic forms; have no smell or taste .

• It can be poured up to one week after impression making It can be poured up to one week after impression making with acceptable clinical results. with acceptable clinical results.

• Increases in temperature increase the rate of reaction and Increases in temperature increase the rate of reaction and shorten the setting time . shorten the setting time .

• The putty consistency should not be mixed with latex The putty consistency should not be mixed with latex rubber gloves. rubber gloves.

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Polyether Rubber Impression MaterialsPolyether Rubber Impression Materials

• The polyether impression material is the The polyether impression material is the stiffest of the impression of the elastomers stiffest of the impression of the elastomers when set. when set.

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Composition:Composition:

• Polyether rubber impression materials are supplied as a base & catalyst system. The base is a moderately low molecular weight polyether containing ethylene amine terminal groups.

• The liquid polymers are mixed with fillers to provide rigidity. Oils are added as Plasticizers to enhance the mixing and handling characteristics of the material. The set materials also are distributing as two- paste system.

• The catalyst paste contains an aromatic Sulfonic acid that enhances the further polymerization & cross- linking of the polymer chains during the chemical reaction. This reaction is responsible for transforming the paste into a stiff polyether rubber.

• Some clinicians suggest using this material for impression of a few teeth or a quadrant, because of its tremendous stiffness.

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PropertiesProperties • Working time is short enough that the viscosity noticeably

increases during the mixing of the material.

• The dimensional changes of polyether is lower than that of any other rubber impression material except the addition silicones, but if it stored in contact with water it absorbs water & changes dimension .

• The permanent deformation is less than that of Polysulphide.

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• The aromatic Sulfonic acid catalyst can cause skin The aromatic Sulfonic acid catalyst can cause skin irritation & direct contact with the catalyst should irritation & direct contact with the catalyst should be avoided. be avoided.

• Hydrophilic (good wettability for easy cast Hydrophilic (good wettability for easy cast forming) . forming) .

• Good surface detail, it has low tear strength. Good surface detail, it has low tear strength. • Some have unpleasant taste. Some have unpleasant taste. • It should be poured within 2 hours . It should be poured within 2 hours . • High stiffness is indicated by low flexibility. High stiffness is indicated by low flexibility.

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Disinfection of rubber impressionsDisinfection of rubber impressions

• A variety of disinfectants were used: A variety of disinfectants were used: • Neutral Glutaraldehyde. Neutral Glutaraldehyde. • Acidified Glutaraldehyde. Acidified Glutaraldehyde. • Phenol Phenol • Iodophor Iodophor • Chlorine Dioxide. Chlorine Dioxide.

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Rubber Materials For Bite RegistrationRubber Materials For Bite Registration

• In the past it was done using bite registration In the past it was done using bite registration Waxes. Waxes.

• The following Shortcoming were associated with The following Shortcoming were associated with the use of Bite registration Waxes: the use of Bite registration Waxes:

• Distortion on Removal. Distortion on Removal. • Release of Internal Stress on Storage. Release of Internal Stress on Storage. • High Flow Properties. High Flow Properties. • Large dimensional changes from mouth to room Large dimensional changes from mouth to room

temperature. temperature.

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• Recently, polyether and addition Silicone Recently, polyether and addition Silicone rubbers have been used to register the bite. rubbers have been used to register the bite. Based on their properties (Short working Based on their properties (Short working time, low strain in compression, low time, low strain in compression, low dimensional changes) the rubber bite dimensional changes) the rubber bite registration materials are superior to waxes registration materials are superior to waxes

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Failure with impressionFailure with impression

1.1. Poor reproduction of surface detailsPoor reproduction of surface details

- rough or uneven surface, due to - rough or uneven surface, due to uncompleted set, premature removal, uncompleted set, premature removal, unproper mixing, contamination.unproper mixing, contamination.

- air bubbles, due to rapid set, unproper - air bubbles, due to rapid set, unproper mixing, surface contamination.mixing, surface contamination.

- irregular shaped voids, due to surface - irregular shaped voids, due to surface contamination and premature movement.contamination and premature movement.

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2. Poor fit2. Poor fit

- distortion… due to adhesive failure between - distortion… due to adhesive failure between tray and imp material, tray not sufficiently rigid, tray and imp material, tray not sufficiently rigid, excessive seating pressure, movement of tray excessive seating pressure, movement of tray during setting.during setting.

- casting too big or small….inappropriate - casting too big or small….inappropriate impression technique, imp poured too late or to impression technique, imp poured too late or to early (insufficient time for elastic recovery), early (insufficient time for elastic recovery), impression stored under wrong conditions.impression stored under wrong conditions.

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Choice and use of trayChoice and use of tray

• Avoid flexible traysAvoid flexible trays

• Use perforated traysUse perforated trays

• Make sure the tray is cleanMake sure the tray is clean

• Apply only a thin layer of adhesiveApply only a thin layer of adhesive

• Wait appropriate time before taking impressionWait appropriate time before taking impression

• Do not mix adhesives and impression materialsDo not mix adhesives and impression materials

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Bad impressionBad impression

• Extra chair-side timeExtra chair-side time

• Repeat visit for patientRepeat visit for patient

• Patient distressPatient distress

• Waste of expensive materialsWaste of expensive materials

• Remake bill from laboratoryRemake bill from laboratory

• Spoil relationship with laboratorySpoil relationship with laboratoryIt was considered impossible to produce satisfactory It was considered impossible to produce satisfactory

restorations in up to 13% of the impressions.restorations in up to 13% of the impressions.

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Shrinkage of imp material towards the tray resulting in the production of a model which is slightly larger than original

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We finished Biomaterial course!

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