Download - FDP Impressions

8/11/2019 FDP Impressions

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Impressions in FDP


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CLASSIFICATION OF IMPRESSIONMATERIALS

BASED ON SETTING MECHANISM

1. Reversible ( Temperature changes)

2. Irreversible( Chemical changes)

BASED ON MECHANICAL PROPERTIES

1. Rigid ( Edentulous ridge )

2. Elastic ( tooth form )


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ELASTIC

IMPRESSION MATERIALS


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WHAT IS AN IMPRESSION MATERIAL ?

ANY SUBSTANCE OR COMBINATION OF

SUBSTANCES USED FOR MAKING AN

IMPRESSION OR NEGATIVEREPRODUCTION ..


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ELASTIC IMPRESSION MATERIALS

1.Aqueous irreversiblea) Alginate

2. Aqueous reversiblea) Agar

3. Non aqueous irreversible

a) Polysulfidesb) Polyethersc) Condensation siliconed) Addition silicones


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HISTORY

These materials were developedto mimic natural rubber whenthere was shortage duringWorld War II

They are classified as synthetic

rubbers

ADA Specification no. 19

The first synthetic rubberlike

materials were produced by aprocessVulcanization orcuring


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Classification of Elastomers based on Viscosity :

a) light body

b) medium body

c) heavy bodyd) putty

Addition silicones available in ( Extra-low andmonophase too )


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Elastomers

Term rubber and elastomer are scientifically identicaland interchangeable

Rubber generally referred to natural rubber

Elastomer is synthetic

They are a special group of a wider group calledpolymers

Made of long flexible chain or string like molecules


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The inside of rubber can be imagined as pile of cookedspaghetti

Each chain of elastomers will be joined occasionallyalong its length to one or more nearby chains with fewchemical bridges

Called cross links

Whole structure forms a coherent network whichprevents the chain from sliding past one another

The process by which cross links addedvulcanisation


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MIXING SYSTEMS

Three systems available :

1) Hand mixing

2) Static automixing

3) Dynamic mechanical mixing


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Hand Mixing

Impression paste dispensed from collapsible tubes

Equal length of base and catalyst taken

Initial mixing in circular motion

Final mixing with broad strokes of spatula

Mixing accomplished in 45 seconds

In case of two putty system kneading with fingers is

performed


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Kneading with fingers


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STATIC AUTOMIXING

Base and catalyst in separate plastic cartridges

Cartridge placed in mixing gun having 2 plungers

The base and catalyst forced through static mixing tip containinginternal spiral

The two components folded over each other many times as theyare pushed through the spiral

Uniform mix obtained


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DYNAMIC MECHANICAL MIXING

Catalyst and base supplied in large plastic bags housed in acartridge

Inserted on top of mixing machine

Plastic mixing tip ( motor driven ) in front of the machine

Parallel plungers push collapsible bags

Material forced into the mixing tip

Mixing accomplished by rotation and forward motion

Thus higher viscosity material mixed with ease


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Problems in hand mixing :

possibility of contamination

more air incorporation

more material wastedmight not be a uniform mix (homogenous)

Vigorous mixing while hand mixing can lead toincorporation of air


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Mixing tips : available with 11 and 13 spirals

the spirals participate in shear thinning of material thus giving us

more working time ..

material mixed with 13 spirals cant be mixed with 11 spirals as the no.

of spirals might not be enough to provide a homogenous mix

In automix after the first ejection of material the tip should be placed in

the material and further material ejected to avoid air incorporation


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Automixing and dynamic mixing in comparison to

hand mixing ::superior physical properties

uniform mix

reduction of voidsavoidance of contamination

During automixing air can get incorporated whileplacement of cartridge in the gun .. Incorporating lotof air before closing it in the gun


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( accdg to an article by JUNGNAM et al )

dynamic mixing was given overall preference to

automixingon the basis of following criteria

ease of mixing

control of loading

quality of mixing

level of cleanliness

contamination

Duration of mixing for dynamic mixing was said to beslower than automixing


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Ideal Requirements

Dimensionally stable Radioopaque Tear resistance Hydrophillic No reaction by products Easy to use Superior colour No odour

Biocompatible accurate surface detail reproduction Maintain accuracy with multiple pours Optimal working time


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Elastic recoveryaddition > condensation > polyether > polysulfide

A set impression must be sufficiently elastic so that it will

return to its original dimensions without significant distortion

upon removal from mouth


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Flexibility of the material is related to the

Glass Transition Temperature( low temperature behaviour)

GTT of different elastomers is differentEg . Natural rubber it is70 C

Therefore it means below this temperature the material behaves like

glass and on hammering can break like glass.

GTT is generally a range 10 degrees

At a temperature above GTT the material will be rubbery .

( flexible )

Strictly speaking we should we should only use the termelastomer to describe a material only if it is above its GTT


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HIGH TEMPERATURE BEHAVIOUR

The upper temperature to which the elastomer can be used dependson its chemical stability

At high temperature the elastomer gets attacked by oxygen

This attack results in a chemical reaction

2 type of reaction

a) degradativebreaks cross linksmakes rubber soft

b) addition of cross linkshardens the rubber


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Dimensional shrinkagepolysulfide > condensation > polyether > addition

The amount of shrinkage a material undergoes once thepolymerization process is allowed to proceed

Factors which cause dimensional shrinkage :

1) loss of reaction by products2) polymerization shrinkage

3) thermal contraction

Polysulfides and condensation silicones have highest dimensionalchange during setting ( 0.40.6 ) %

shrinkage here is due to evaporation of volatile by products and

rearrangement of bonds with polymerization


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Addition silicone have a dimensional change of

maximum of 0.15 %

Polyether dimensional change0.2%

Less in addition silicone and polyether as there are no reactionby products

Dimensional stability is important if the impression has to besent to the lab and impression poured for that time the

material should be dimensionally stable


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Dimensional accuracy :-

1) Greatest dimensional accuracy occuring

immediately after polymerization complete

2) But declining as the impression is stored for extended

periods of time

3) pvs and polyether dimensionally stable for

1-2 weeks after taking impression

4) polysulfide accurate if poured within 1-2 hours of makingan impression


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Tear strengthpolysulfide > polyether > addition = condensation

Tear strength refers to the property of the material to resisttearing when removed from undercuts

In deep sulcus the impression can tear thus compromising theaccuracy of the impression

While retrieving the cast from the impression the material mustnot tear so that repeated pours can be made


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Hydrophillicity

Also referred to as Wettability relates to the ability of amaterial to flow in small areas

Impression that wet teeth well , displace moisture wellcreate

less voids

If material has high wetting angle it does not flow in smallcrevices ( thus not a good material for FPD )

For FPDmaterial must reproduce detail in area of 20-70 m

For RPD100-150 m of detail reproduction is ok


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Hydrocolloids , Polyether , Polysulfides have relatively lowcontact angle

PVS requires surfactants to lower contact angle

They are non ionic surfactants , they have a hydrophillic partwhich is towards the surface and the silicone compatible

hydrophobic part which is towards the material

Silicones are intrinsically hydrophobicsurfactant ( surfaceactive additive )

When impression material with surfactant comes in contact withmoisture surfactant has to migrate to surface .

This prevents hydrophillicity to fully develop at very first contact

with moisture


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Polyether is intrinsically hydrophillic from the time its

mixed until it sets it is characterised by its tendency to favourmoist surfaces

It captures accurate impressions in presence of saliva and blood

Hydrophillicity is needed when syringing the material and seatingthe tray

New surface of material generated as it contacts the saliva

This is the point when hydrophillicity is needed for clinicalsuccess


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Hydrophillicity of polyether and polysulfide is due to thefunctional group that attract and interacts with water molecules

via hydrogen bond

Hydrophillic group

1) polyether : C=O ( carbonyl )

C-O-C ( ether )2) polysulfide : S-S ( disulfide )

S-H ( mercapton )

Silicone is hydrophobic because of the hydrophobicaliphatic hydrocarbon group around siloxane bond


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POLYSULFIDE

First elastomeric impression material introduced in1950

Supplied in 2 pastes ( Base and Accelerator )

Available in 3 consistencies ( low,medium, heavy body )


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COMPOSITION

BASE :

Polysulfide polymer

Titanium dioxide ( filler )

Dibutyl Pthalate ( plasticizer )

Sulfur (to enhance the reaction)

CATALYST:

Lead dioxide ( to react with polysufide)Dibutyl Pthalate ( plasticizer )

Titanium dioxide ( filler )

Oleic / Stearic Acid ( retarders )


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Impression should be poured within 30 min following removal

from mouth ( because in 1st

hour the material undergoes 50%of the 24 hr shrinkage

Refrigeration prolongs shelf ( but the material must not beimmediately used as the condensed water on it will shorten its

working time

Water is not only the by product but also the catalyst

Storage under warm condition shortens shelf life

Custom tray made must not be used on the same day as itundergoes 90% polymerization shrinkage during 1st 8- 10 hours


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Problems

During setting polymer contracts during cross linking

Loss of by product ( water ) on evaporation

The impression may imbibe water

Incomplete recovery of deformation

Bad odour

Second pour less accurate


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Points to remember !!!!!!!!

Temp working time and vice versa

Altering base : accelerator ratio can help but

a) affect mechanical property

b) not economical (as some paste is not used)

Disinfection using10% soln. of sodium hypochlorite for 10

min . Prolonged immersion can produce minimal distortion


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Minimize the amount of material for making

impression

Use tray adhesive ( eg . For Polysulfides -- butyl

rubber / styrene acrylonitrile ) with suitable solventchloroform / ketone

Heavy body materialbetter dimensional stability as ithas lower concentration of reactive groups thusproducing fewer by-products


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Condensation Silicone

Introduced in the year 1955

Supplied as:

a) Two paste

b) Paste liquid catalyst system

Available in 2 consistencies

( low and putty )

Putty developed to overcome large polymerisation shrinkage

Also called room temperature vulcanization silicone


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Composition

Base paste :

a)hydroxyl terminated polydimethyl siloxaneb) ortho alkyl silicate ( cross linking agent )

c) silica ( inorganic fillers )

Catalyst paste or liquid

a) stannous octate ( catalyst )

b) ortho alkyl silicate ( cross linking agent )

c) thickening agent ( in case its a paste )


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Points to Remember

Biologically inert

Not radiopaque

Putty wash technique of impression making applied

Setting shrinkage because of loss of volatile by product

Thus cast to be poured within 30 min of making an impression

Hydrophobic thus requires dry field difficult to pour stone


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Addition Silicone

Introduced in the year 1975

Also called vinyl siloxane orvinyl polysiloxane

Supplied as two paste system and

putty in jars


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Available in 5 consistencies

(ultra low , low , medium , high, putty and monophase )

Traditionally hydrophobic

Surfactant added to make it hydrophillic


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Composition

BASE:

a) polymethyl hydrogen siloxane

b) filler

CATALYST:

a) divinyl polydimethyl siloxane

b) fillerc) chlorplatinic acid (accelerator)


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Points to remember !!!!!!

The polymerisation reaction has no by products

No impurities

If proportions out of balance then hydrogen gas is formed as byproduct

It can leave pin point voids on the stone casts if pouredimmediately


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Palladium or platinum added to scavange the hydrogen gas

Surfactants added allow the material to wet soft

tissues better

Surfactant used is polyether carbosilane

Still they are relatively hydrophobic

Monophase materials are the current trend (one mix of thematerial is used for both syringe and tray)


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Fast setting and regular setting materials available ( no diff inproperties )

Multiple casts can be poured with same accuracy

Biocompatible

After polysulfide or polyether has been used avoid using pvs

material as the two materials leave a chemical film in the mouththat inhibits the setting of pvs


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The polymerization reaction requires a platinum catalyst

Sulfur or sulfur compounds eg. From latex gloves , rubber damcan interfere with the platinum catalyst thus affecting thepolymerization reaction

This causes the surface of the impression to remain tacky as thepolymerization is not complete

Preparation and adjacent soft tissues can be cleaned with 2%

chlorhexidine solution to remove contaminants


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Putty reline technique used

putty impression serves as the custom tray

Stops used on trays to prevent pushing through wash

material when putty seated

Dimensional stability of monophase better than

polysulfides and condensation


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Wash impression


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Final Impression


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Disinfectiondone by a) 10% hypochlorite b) 2%gluteraldehyde ( immersion not greater

than 1015 min . ) as the surfactant might leach out and makethe material hydrophobic

Hydrophobic materials have water contact angle of 95 degreeshydrophillic 30-35 degrees

Dilute soln of soap is active surfactant

Can be poured even 1 week after impression


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Polyether

Introduced in Germany 1960

This was the first material developed primarily tofunction as an impression material

Available in ( low , medium , high ) consistencies

Supplied as 2 pastes


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Composition

BASE :

a) low molecular wt. polyether with

ethylene imine terminal group

b) colloidal silica ( filler )

c) glycoether or pthalate(plasticizer)

CATALYST :

a) alkyl aromatic sulfate ( initiator )b) filler

c) plastcizer

P i b !!!!!!


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Points to remember !!!!!!

Material is radiolucent

No reaction by product

Can be poured immediately , after several hours , after severaldays too

Multiple pours accurate

Material has tendency to absorb water or fluid and leach out

water soluble plasticizer ,thus the stored impression must beplaced in a cool dry place


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The only accurate impression material that sets faster thanpolyether agar

Both stock and custom trays can be used

Disinfectionimmersion in 2% gluteraldehyde for 10 min ,chlorine compounds or iodophors

Bitter taste objectionable to some patients

High stiffness after setting

d d l


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Rigid , does not tear easily

Enables the dentist to get good subgingival detail without tearingimpression on removal

Material adheres to itself : thus used in correctable impressiontechniques ( border moulding )

Improved polyether : ( soft polyether , easy to remove ,maintains rigidity for wide range of aplications can capture finedetail in moist conditions )

S b h i i d ll i l


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Snap set behaviour is seen : does not allow material tostart setting before working time ends

When it does set it does so immediately

Since they are hydrophillic care to be taken whiledisinfectingto prevent swelling

Spray with disinfectant for 10 min , rinse and dry

immediately before pouring cast

Setting not contaminated by latex gloves


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Rigidity of the material makes it the material ofchoice for taking impressions for implants

It keeps the tray from distorting in case ofcrown and bridges avoid using polyetherbecause of its rigidity . To avoid pulling out

of restoration

Vi ibl Li ht i El t i I p i


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Visible Light-curing Elastomeric ImpressionMaterial

Based on Polyether urethane dimethacrylate

Visible light cure photoinitiators and activators used

Single component system

Syringe contains light body material

Tubes contain tray material

Transparent tray used


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Problems

Ability to set completely against wet field

Cross-linked material stiff

Direct the light to all areas of the mouth so that

material cures completely

N Ad !!!


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New Advancement !!!

Colour changing elastomer !!!

Zhermack patented product

Technology usedchromatime technology

Colour change indicates impression is entering settingstage

Colour changes from green to yellow of the washimpression

Indicates the end of working time in the mouth


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Impression Techniques


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Copper tube or band technique


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Impression making with hydrocolloid

Two impressions are made

a section (quadrant) impression for die

a full-arch impression for working cast

adequate anaesthesia checked. If the impression isbeing made at a separate appointment - anaesthetise thearea again.

Tray selection done


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Laminate Technique

Combination of Agar and Alginate Impression Materials

The tray hydrocolloid is replaced with a mix of chilledalginate, that bonds with syringe agar

Gelation

The alginate gels by chemical reactionAgar - contact with cool alginate


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Advantages

Less preparation timeLess complicated when compared to the wet field technique

Disadvantages

Bond between agar and alginate is not strong

High viscosity alginate displaces agar during seating

Dimensional inaccuracy of alginate limits the use to single

units


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ELASTOMERIC IMPRESSION MATERIALS

Techniques

Monophase technique

Simultaneous putty/wash technique Two step putty/ wash technique

Double viscosity double bite technique

Laminar technique Matrix impression technique


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Tray Adhesive

Tray adhesives are specific for each material

Two types1) paint on2) spray on

Tray adhesives provide a bond between impression material and the tray

two coats of the tray adhesive has to be applied and wait for 510 min.. For it todry otherwise the adhesive will interfere with the polymerization reaction

Tray adhesive if not applied can affect dimensional stability as there might be adebonding of tray with the material thus displacing the impression .


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( JPD2005 ; 94 : 209-213 )

paint on adhesives better than spray on adhesives and adhesivesrecommended by manufacturers ..

spray on probably produced a thinner coat ..

the tray adhesive probably was a weaker link as compared to the tear strength

of the material caused the failure at trayimpression , adhesive- impressioninterface . Causing dimensional instability

The base of the tray adhesive in silicone elastomers may contain a reactivesilicone eg . Poly dimethyl siloxane and ethyl silicate the latter producing aphysical bond with impression tray resin


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New development !!!!!!

Unique advancement in impression trays:

The Directed Flow Impression Tray. This new, single-use tray eliminatesthe need for a tray adhesive, simplifying both preliminary and finalimpressions

The Directed Flow impression tray includes :

1) A self-retentive fleece strip designed to hold the impression materialsecurely in the tray (eliminating any need for a tray adhesive.)

2) This means fewer handling steps.

3) Saving an estimated five minutes per procedure . No more unpleasantodor or mess from a tray adhesive.

In addition, the retentive fleece features striations that


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act as a barrier to avoid tooth/tray contact and occlusalflat-spots for better impression results



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MULTIPLE MIX TECHNIQUE :

1. Two separate mixtures required

2. Light and heavy body mixed simultaneously (by different person )

3. Tray filled with heavy body (uniform thickness)

4. Syringe loaded with light body


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5. Light body injected in the mouth within and around tooth preparation

6 Tray is then inserted in the patients mouth and seated over syringe material

7. The two materials should bond together on setting

8. The heavy body will force the light body to adapt to the prepared areasensuring accurate detail


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PUTTY WASH TECHNIQUE

1. This was developed for condensation silicone to minimize theeffect of polymerization shrinkage

2. Nowadays manufacturers of addition silicone also make putty

material for this technique

A. TWO STAGE PUTTY WASH TECHNIQUE

1. Thick putty is placed in a stock tray and a preliminaryimpression is made

2. This is like a custom tray


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Putty-wash or reline technique


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3. Now some space is created for the wash material

4. This is done by cutting away some of the tray putty

5. Space can also be created by placing polyethylenesheet as a spacer between the putty and the preparedteeth

6. A mix of thin wash material is placed in the putty tray

and seated in the mouth for the final impression


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B. SINGLE STAGE TECHNIQUE

1. Light body wash material is syringed into place

2. Now unset putty is seated over it

3. The putty may displace light body and push through

4. To avoid this occlusal stops should be used in the tray

Si l P /W h T h i


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Simultaneous Putty/Wash Technique

Apply thin layer of adhesive unless mechanicalretention is assured

Mix equal amounts of putty base and putty catalyst

until streak free. At the same time the assistant mixes the light body

Choose a spatula large enough to pick up the mixedimpression material

But pliable enough to mix the material against the pad.


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First use a circular motion combining the two strands

Then use figure eight motion to blend and flatten onthe mixing pad.

Roll putty into an elongated cylinder.

Insert into the stock impression tray.

By the time assistant finishes mixing the light bodymaterial the unset putty material should already be on

the tray.


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Load the syringe with wash material.

Syringe wash material around the preparations & on theocclusal surface of the teeth in impression.

Make a large dimple in the putty in the area of

preparation so all margins are covered with washmaterial.

Fill the dimple with wash impression material.

Slowly seat the filled tray and immobilize until set.

h d bl


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Heavy & Light Body Using Double Mixing

Techniques

A stock tray is usually selected, coated with adhesive.Gingival retraction is done

Putty base and catalyst are kneaded together until a homogeneousmix is attained.Load putty into trayCover surface with polyethylene sheet to act as spacer

Place the loaded tray in mouth with a rocking motion to eliminateundercutsWait till initial set.( 2 min)


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Then check clinically by a fingernail rebounding.

Remove the impression.The spacer is removed, excess material & if more space is required

still more material is removed by a knife or acrylic bur & the trayset aside.

Carefully remove retraction cord.Mix wash material & inject around preparations & occlusal surface

of teeth using a syringe

Load remaining material in preliminary putty impression

Slowly but firmly seat tray over the teeth to take the finalimpression

Cl d Bi D bl A h M h d


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Closed Bite Double Arch Method

also called Dual quad tray, double arch, triple arch, &

closed mouth impression


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Advantages

1.Physical deformation of the impression by themandible during opening is minimized.

2. Seating of teeth during maximum intercuspation is

captured.3. Less material is needed & patient is morecomfortable.

4. Less gagging.


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Disadvantages

1.Tray is not rigid- depends on the impression materialrigidity.

2. Not a functionally generated techniqueso limited toone casting per quadrant.

3. Distribution of material is not uniform.


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Types of Dual Arch Trays

MetalPlastic

Both with or without side walls.

Depending on the Location

Posterior\anterior sextantQuadrant

3/4 of an arch

Full arch.


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Technique:

Evaluate fit of the tray by checking the distal cross barextent

Check for bilateral closure & patient comfort.

Gingival retraction is done.

Load one dispensing gun with lighter body

Light body is injected around the prepared tooth (an intra

oral tip can be attached directly to the mixing tip)


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Putty is inserted on both sides of the tray and the patientis asked to bite in centric occlusion.

After waiting for the set (2 mts), the patient is asked toopen the mouth

The tray adheres to one arch.

After placing fingers on either side of the tray it isremoved with equal pressure bilaterally to minimize thedistortion.The handle should not be used for removal of the tray

The impression is then washed & checked.

Laminar Technique


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Laminar Technique

Load the dispensing gun with heavy body A preoperative impression is made. Impression of the tooth to be prepared is relieved to a

depth of 0.5mm in the cervical area.

Two holes are drilled from the buccal surface, one on themesial and one on the distal. The tray is reinserted Low viscosity impression material is injected through the

mesial hole and the excess will flow through the distalhole.

MONOPHASE VISCOSITY


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MONOPHASE VISCOSITY

TECHNIQUE

Used with medium viscosity of polyether

Only a single mix is made ( Part placed in tray andanother part used as a syringe material

Success lies in the pseudoplasticity of these two materials

Monophase Technique


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Monophase Technique

Apply thin layer of tray adhesive until mechanicalretention is assured.

Allow it to dry for 5 min.

Load dispensing gun with monophase cartridge Load the tray with monophase bodied material Attach intra oral tip to the mixing tip Syringe wash material around clean dry preparations &

occlusal surface of other teeth Slowly seat the loaded tray & immobilize until set.


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Monophase (polyether)

Tray and Syringe Impression made

material

Matrix Impression System


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Matrix Impression System


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Features of the refined Matrix


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Mounted fast cut stone is used to relieve internal walls of eachpreparation 0.25 to 0.50 mm

Trimming of the matrix is thus complete

The internal incisal / occlusal aspect of the matrix should not betrimmed

All external aspects of the matrix should be abraded

Features of the refined Matrix

Making The Impression


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Placement of refined matrix on the prepared teeth Selection of stock tray

Matrix filled with low viscosity impression material



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Removal of retraction cords Syringe material dispensed around the

prepared teeth

The filled matrix is seated on theprepared teeth with vertically directedforce

Removal of polymerized matrix

impression

Advantages


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Advantages

1.Effective retraction of gingival tissue

2.Effective Hemostasis

3.Effective method of sulcular cleansing

4.Effectively controls the forces that act on gingiva & holdsthe sulcus open.

5.Forms optimal flange configuration


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6.Overcomes the defect of older systems

7.Delivers impression material into the sulcus with speed &gentleness but with accuracy.

8.Allows segmentation of complex impression

9.Delivers full arch impression.

10.Renders FPD impression to be a much predictable

sample

Di d t


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1.Incomplete seating of crowns

2.Distortion due to elastic properties of impression materials

3.Delamination due to non bonding of materials

Disadvantages

Types of Failure CausesRough or uneven surface onimpression

Incomplete polymerisation

Too rapid polymerisation


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pToo rapid polymerisation

Excessively high accelerator / base ratio

Bubbles Too rapid polymerisation

Air incorporated during mixing

Irregularly shaped voids Moisture or debris on surface of teeth

Rough or chalky stone cast

Inadequate cleaning of impression

Excess water left on surface of the impression

Premature removal of castImproper manipulation of stone

Distortion Resin tray not aged sufficiently , still undergoing

polymerization shrinkage

Lack of adhesion of rubber to tray

Development of elastic properties before tray isseated.

Excess bulk of material

Insufficient relief for reline material

Movement of tray during polymerisation

Premature removal from mouth


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Rebound of Putty Void due to Improper

Mixing of Material

Distortion due to excessive pressure applied after materialh d l d l l


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has developed initial elasticity


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Thank You