fdp impressions
TRANSCRIPT
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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
Impression Techniques
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Impression Techniques
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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Making The Impression
Placement of refined matrix on the prepared teeth Selection of stock tray
Matrix filled with low viscosity impression material
Making The Impression
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Making The Impression
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