04 Impression Materials 2013

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Impression

MaterialsPresented byDr. Mohamed Abdel Aziz

Lecturer of fixed prosthodontics


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IMPRESSION

Definition:

An impression is a negative imprint of the

prepared teeth or tooth and their relation to

the surrounding structures.


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An acceptable impression for cast restoration

should meet the following requirements:

1-It must be exact record of all the aspects of the

prepared tooth and sufficientunpreparedtooth

structure immediately adjacent to margins, to

allow the dentist and the technician to be certain ofthe location and configuration of the finish line.

2-Other teeth and tissue surrounding the abutment

tooth must be accurately reproduced topermit

proper articulationof the cast and contouring of

the restoration.

3-It must befree from air bubblesespecially in the

finish line area.


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1- Easy to mix and handle.

2- Suitable working time.3- Suitable setting time.

4- Compatible with die and stone

materials.

5- Not toxic or allergic to the patient.

6- Dimensionally stable on setting.

The IdealImpression MaterialMust

Meet The Following Requirements:


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7-Accurate to record the fine details of the

prepared tooth8-Has acceptable odor and taste.

9-Adequate strength.

10-Adequate shelf life.11-Economic.

12-Ready to disinfected without loss of

accuracy.13- Fluid or plastic when inserted into the

mouth.


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Classification of the Impression Materials:

Non elastic Impression Materials

Plasters

Impression compound

Zinc oxide and eugenol

Some waxes

Impression materials are classified to their setting

behavior into:


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Reversible

IrreversibleHydrocolloids

Polysulfide

Condensation silicone

Polyether

Addition silicone

Elastomeric

Classified according theirchemistry

Elastic Impression Materials


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Uses of non elastic imp. Materials in FPD:

Non elastic imp. Materials are hard, they lock into

undercuts therefore they are not suitable as final

imp. For FPD (fixed partial denture) but they haveother uses:

(a) Plaster:

Presentation: powder mixed with water to form a

smooth pasteAdvantages:

- Accurate can record fine details.- Easily assembled when fractured.

Uses: as an accurate template for soldering

Non elastic impression material


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(B) Impression Compound:

Presentation: CAKES OR SHEET FORM: used aspreliminary impression for complete dentures.

BROWN STICKS: used for single copper bandimpression

GREEN STICKS: used as above and modifications forspecial trays

Advantages: does not need gingival retraction as thecopper band causes tissue displacement.


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(c) Zinc oxide and eugenol:

Presentation: both the base andaccelerator are in the form of pasteUses: in bite registration in conjunction

with a bite registration frame.

(d) waxes:

- Blue inlay wax: used for wax pattern

construction.- sticky wax: used for soldering.- molding wax: used as a bite registrationmaterial.


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I- Hydrocolloids

They are suspension of small solid particlesdispersed in liquid (dispersion) when the

dispersion medium is water it is called hydrocolloids (aqueous impression material).

The conversion from sol to gel can be achievedthrough:-

- Chang in temperature reversible change- Chemical reaction irreversible

change

Elastic impression materials:


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(A)Reversible hydrocolloid: (Agar-agar)

It is a polysaccharide constituting 8-15% by weightagar; dental agar is composed of several agar

species extracted from seaweeds. The remaining

constituent is 80% water

Presentation:

It is presented in the form of a semi-solid gel

packaged in polyethylene.

heavy consistency for, tray material

light consistency for syringe material.


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It needs special conditioning equipment.

This conditioning unit is composed of 3 compartments:

1)

The liquefying bath:where the material is placed in boilingwater (100c) for. 10 minutes, reuse of the material needs a

longer immersion time (12 min. )

2) The storage bath:where the material is stored at (63-66c) until

needed it can be stored for up to 5 days.3) The tempering bath:where the material for a suitable

temperature for the mouth (45c)

this is done several minutes

before the patient appointment.


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Advantages of agar impression:

1- very accurate impression material.

2- Hydrophilic gives best results in presence of saliva.

3- Long working time. 4- Low material cost.

5- No custom tray is required.

6- No mixing required


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Disadvantages:

1- Needs special equipments.

2- Needs special type of double-walled trays with water .

Circulating tube in it. (water cooled tray)

3-Low stability due to synersis and imbibition.

4- Low tear resistance.

5- Difficult to disinfect.Precaution: Should be poured immediately for

best results.


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B- Irreversible hydrocolloid material

(Alginate)

It is the most widely used impression material.

Its source is a brown seaweed (algae) named algin, it ismarketed as powder and liquid.

On mixing them a chemical reaction result, which is anirreversible process, so the material can only be used

once. In fixed prosthodontics work it is used for primary

impression to make the study casts


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Advantages:

1- Easily manipulated & mixed.

2- It has suitable setting time.

3- Hydrophilic i.e. can be used in contact with saliva.

4- Low cost

Disadvantages:

1- Has low tear strength.

2- Not accurate i.e. incapable to produce the fine details. 3- Dimensionally unstable due to synersis and imbibition.

Precaution: should be poured immediately.


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II -Elastrometric

Impression materials


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II -Elastrometric Impression materials

These are elastic impression materials called nonaqueous elastic impression material to bedistinguished from the hydrocolloids which are aqueousmaterials.

They are synthetic rubber.

They offered potential solutions to the two mainproblems associated with hydrocolloids:

poor tear resistance and

poor dimensional stability.


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Accuracy= ability to replicate the surface details.

Dimensional Stability = ability to retain itsabsolute dimensional size over time.

Tear Resistance = ability to resist tearing in thinsections (such as through the feather-edged material

within the gingival sulcus.


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Classification:According to chemistry

- polysulfide.

- condensation silicone.

- addition silicone.

- Polyether.

According to viscosity:

- very high (putty).

- High. (heavy body) - medium (regular).

- low (light).

- very low (extra light)


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POLYSULFIDE

Polysulfide is an elastomer that is also

known as mercaptan, or simply as rubber

base.

The impression material is packaged intwo tubes: a base and an accelerator.

Composition:

-The base contains a liquid polysulfide polymer mixed with

an inert filler.-The accelerator, which is usually lead peroxide mixed with

small amounts of sulfur and acts as an oxidation initiator.


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Material properties

1-Reaction:

Condensation Polymerizationwithwaterby product. Thispolymerization is exothermic and is affected significantly by

moisture and temperature.

-High humidityandtemperaturedramatically reduce its

working time , which may be so short

-The polymerization begins before it is inserted in the

mouth, resulting in severe distortion.


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2- Dimensional stability:

Polysulfide rubber base possesses much greater

dimensional stability than does hydrocolloid. However,

There is aslight contraction of polysulfide during

polymerization.

This effects can be minimized by

A-a custom impression tray to reduce the bulk of thematerial.

B-impression should be poured within approximately 1

hour of removal from the mouth or less.


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3-Tear strength:

Thehightear resistance, and enhanced elastic propertiesof polysulfide facilitate impression making in sulcular areas

and pinholes.

4-Setting time:Polysulfide impression haslongsetting time in themouth (about 10 min).

5- Odor:Polysulfide impression hasunpleasantsulfide odor.


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6- Stain clothes:polysulfide materials are polymerized with the aid of

lead peroxides, which explains this material's typicalbrown color. The un polymerized product is sticky and

should be handled carefully, because it stains clothing

permanently.

7-Hydrophobic material

-Special care must be taken to insure that there is no

moisture on the preparation when the impression is made.- Thin layers of moisture that becomes incorporated

during the injecting process can cause voids in the

impression.


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Advantages

1- Good tear resistance.

2-Good flow.

3-High flexibility.

4- Good detail production.

5-Long working time.

6- Low cost.

Disadvantages

1- Long setting time.

2-Pouring within one hour.

3-Unpleasant odor.

4-Need custom tray.

5-Stain clothes.


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Condensation Silicone impression materials utilize

1- A heavy-body "putty"relined with

2- A thin light body "wash."

Condensation Silicone


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1-Reaction ;-Condensation-reaction because of the nature of their

polymerization reaction withalcohol byproduct.

2- Dimensional stability.-The evaporation of thisalcoholis responsible for shrinkage

of the material and resultant poor dimensional stability.

3- Odor ;-Odorless material

-Dimensional stability is less than that of polysulfide but

greater than that of reversible hydrocolloid

Material properties

-The condensation silicones overcame several disadvantages

associated with polysulfide.


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4- Setting timerelatively short setting time in the mouth (about 6 to

8 minutes).

5- Condensation Siliconeis less affected by highoperating room temperatures and humidity.

6- Pouringshould be pouredwithin one hourto avoid dimensional

instability.


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7- Condensation Siliconeis extremelyhydrophobic

for this reason, the prepared teeth and gingivalsulci must be completely free of moisture to make

possible a defect-free impression.

-Pouring without trapping air bubbles is also more

difficult than with other impression materials.

8- Condensation Siliconeis used with astock

impressiontray, no need of special tray


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POLYETHER

Material properties

1-Reaction ;

-Additionpolymerization reaction.

- No volatile by-product is formed, which results in excellent

dimensional stability.

- polymerization shrinkage is unusually low with room

temperature .

2- Dimensional stability.-High dimensional stability .

accurate casts can be produced when the material is poured

more than a day after the impression has been made.


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Impregum L DuoSoft Quick
http://www.google.com.eg/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=3PQRfvLP74DRxM&tbnid=XJTnbggi2x5pxM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.ids-cologne.de%2Fde%2Fids%2Fpresse%2Fausstellerpressefaecher%2Findex.php%3Faktion%3Dsearchb%26p1id%3D%26format%3Dhtml%26base%3D%26tp%3Dkm3%26search%3D%26pmid%3D%26start%3D20%26anzahl%3D10%26channel%3Dids%26language%3Dd%26archiv%3D1&ei=FKsmUbyiDonj4QTj2YCYDw&bvm=bv.42661473,d.bGE&psig=AFQjCNEmux8l9vS9XZYFejbLkM1ch1DbXw&ust=1361574970294011http://cpsmagazine.com/publications-post/new-delivery-method-offers-improved-outlook-on-impression-taking/impregum_full_arch_impressionhttp://cpsmagazine.com/publications-post/new-delivery-method-offers-improved-outlook-on-impression-taking/impregum-soft-polyether


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Short setting time in the mouth(about 5 minutes)which is

less than half the time required for polysulfide.

4- Setting time

3- Pouring

-Accurate casts can be produced when the material is

poured more than a day after the impressionhas been made.

-Polyether is stable only if stored dry, because it will

absorb moisture and undergo significant dimensional

change.


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5- Stiffness of the Material

-The stiffness of the set material causes problems when

separating a stone cast from the impression.

-Thin and single tooth, is liable tobreakunless the

practitioner uses great care.

-Custom made tray is usedto minimize the bulk of thematerial to make it easier to remove the impression from

the mouth and the cast.

6-Odor ;-Odorless material


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Advantages:

1-Hydrophilic in nature so it has

-Better flow in contact with soft tissues.-Better reproduction of the soft tissue and finish line.

-accurate casts

2- Easy handling and mixing.

3- Excellent dimensional stability.

4- Multiple castes can be obtained.

5-High accuracy.

6-Short setting time.

7-Automix is available.


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Disadvantages:

1-Short working time.

2-Stable in dry condition . Absorb moisture resulting in

dimensional change.

3- Stiff material cause problem during separation from the cast

and patient mouth.

4- Low tear resistance.

5-Bitter taste


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ADDITION SILICONE

Also known as (poly-vinyl siloxane) Addition silicone is

generally used as a two-viscosity system, although monophase

formulations are also available.


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Material properties

-Additionpolymerization reaction. has much greater

dimensional stability.

-The set material is less rigid than polyether but stiffer

than polysulfide.

1-Reaction

2- Dimensional stability

-Has greater dimensional stability due to absence of by-products.


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3-Setting time

4-Pouring-Accurate casts can be produced when the material is

poured more than a day after the impression has been made.

-Pouring should be delayed with some of the earlier

products because the porosity of the cast surface caused by

hydrogengasfrom the impression material.-Modification of the formula by the addition ofpalladium

to absorb the hydrogen has minimized this problem..

Relatively short ,can be controlled by changing the base

catalyst ratio.


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5-Stiffness of the Material

-Relatively rigid, difficult to remove from the mouth or

sever undercut.

- Fracture of the die may occur when separating a stone

cast from the impression

6-Odor ;

-Odorless tasteless and clean material.


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-Polymerization retardation of some brands of

impression material, in combination with some brands ofgloves can be observed resulted from sulfur derivatives in

the latex.

-This can even occur indirectly, when the impression

material comes in contact with an object, such as a tooth,that has been touched by a glove, and not with the glove

itself.

-Also can result from contact with other latex items,

such as a rubber dam or even from retraction cord.

-This problem can be avoided by using (non-Latex)

poly-vinyl or poly-Nitrile gloves

or over-gloves during the handling of the impression

material.


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Advantages :

1. -High accuracy.

2. -High dimensional stability.

3. -Pouring can be delayed.

4. -Multiple cast can be obtained.

5. -Dos not stain cloth.

6. -Short setting time.

7. -May be used with stock or custom tray.

8. -Can be silver or copper plated.

9. -Automix is available.


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Disadvantages:

1. -Expensive.

2. -Short working time.

3. -Poor wetting.

4. -Hydrophobic so it is important to dry the field.

5. -Some materials released hydrogen

6. -Setting is affected by some brand of latex gloves due to

sulfur inhibition.


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Comparison of Properties

Working time

longest to shortest

agar > polysulfide > silicones > alginate = polyether

Setting time

shortest to longest

alginate < polyether < agar < silicones < polysulfide

OBrien Dental Materials & their Selection 1997


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Stiffness

most to least

polyether > addition silicone > condensation silicone >polysulfide = hydrocolloids

Tear strength

greatest to least polysulfide > addition silicone > polyether >

condensation silicone >> hydrocolloids



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Cost

lowest to highest

alginate < agar = polysulfide polyether > polysulfide >condensation silicone > hydrocolloid

Phillips 1996



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Wettability best to worst

hydrocolloids > polyether > hydrophilic addition

silicone > polysulfide > hydrophobic addition silicone= condensation silicone

Castability best to worst

hydrocolloids > hydrophilic addition silicone >polyether > polysulfide > hydrophobic addition silicone= condensation silicone



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IMPRESSION TECHNIQUE


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I- Single mix impression technique:-This technique need custom made tray painted with

adhesive .

-The material is supplied as a medium viscosity type.

-Equal length of base and catalyst are mixed thoroughly.


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-An impression syringe is used to drive the material in

the sulcus and the preparation.

-The other part is loaded in the custom made tray to be

seated in the patient mouth over the injected material.


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-Part of the mix is injected around the prepared teeth

after removal of retraction cord and gentle drying with

compressed air.

-Then the custom made tray is seated in the patient mouthover the injected material.


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II- Double mix impression technique:

(One step)

-This technique , two different viscosity the material is used .

Heavy and medium or heavy and low. custom or with adhesive or

stock tray is required


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-Medium or low viscosity mix is injected by a syringe

around the prepared teeth after removal of retraction cordand gentle drying with compressed air.


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-The heavy viscosity is mixed and loaded on the tray and seated

on the patients mouth over the injected material.


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III D bl i i i h i


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III- Double mix impression technique:

(two step) (Putty and wash technique)

-This technique used a stock tray. A putty or heavy body

impression is made on the stock tray to produce putty tray similar

to the acrylic resin custom tray.

-Over which a wash of low viscosity material is applied to

record. The fine detail of the prepared teeth, adjacent teeth and

oral structure.

better than the double mix technique because

1-The set putty or the heavy body material force the wash

material to record the preparation details .

2- Eliminate the step of custom made tray construction so

save time.


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-A space for wash material should be created either by:

1-taking it from the patient mouth before the preparation2-- covering the material by polyethylene strip as spacer for the

wash material.

3-selective relief of the set heavy body impression using sharp

scalpel.


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S


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Steps:

1-Before preparation select a stock tray that fit the arch.

The putty material is mixed by clean hand by kneading it usingsqueezing motion until the material become streak free.

2-Roll it in the form of rod, put it inside the tray and insert it in

the patient mouth and keep it under light pressure.


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3-After setting remove from the mouth remove

the excess and undercut using scalpel.

4-After preparation and tissue retraction cord the light


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4-After preparation and tissue retraction cord the light

body or wash material is mixed on the glass slab with spatula

until the mix is free from streaks of catalyst, loaded some of

the mix in a syringe and the rest on the putty impression.5-The mix is injected by a syringe around the prepared

teeth after removal of retraction cord and gentle air drying

then seat the tray firmly in place until complete

polymerization.

6 Seat the tra slo l ntil it is firml in place


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6-Seat the tray slowly until it is firmly in place.

7-The tray should be held in place withnodownwardpressure for 6 minutes.

8-Pressure exerted on the tray while the wash is

polymerizing will produce stresses in the semi-rigid putty

lining the impression tray.

-When the impression is removed from the mouth, the

stresses will relax, resulting in deformation and distortion

of the impression.

After the material has set, remove the impression as

quickly as possible to prevent plastic deformation of the

material.


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IV- Dual Arch Technique:Closed mouth technique

-It is called triple tray technique . It is used for making

impression for single unit.

-The impression is made at maximum intercuspation using high

viscosity polyether or additional silicon supported by thin mesh in aframe.


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Th i l i i h i


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The optical impression technique:

-It depends mainly on the computer for designing andmanufacturing all-ceramic inlays onlays crowns at chair side .

(CAD CAM )

-After teeth preparation a thin layer of opaque powder is

sprayed over the preparation to reflect the light.


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A small hand held camera is placed over the preparation to

take an optical impression of the prepared teeth

The image of the preparation is transmitted to the


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g p p

computer screen.

The design of the restoration is made and the recorded

data is transferred to small milling machine to fabricate therestoration from a prefabricated ceramic blocks.


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Advantages:

1-The restoration finished in single visit .

2-Coventional impression and laboratory techniquesare eliminated

I i i i


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Impression inaccuracies

Visible flaws

related to impression technique which occurcommonly include:

Finish line not visible

Air bubbles in critical places

Voids or drags Unset impression material on surface of

impression and cast

Finish line not visible??


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Inadequate soft-tissue management

Sulcus impression tearing because ofinadequate bulk

Tendency of the gingival cuff torecoil and displace partially setimpression material

Bleeding from inflamed gingivadisplacing impression material

Retraction cord (plain or impregnated)

Two-cord technique Rotary curettage ElectrosurgeryLaser troughing



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mixing

tray loading

syringing

tray seating

Mixing andDeliverySystems

hard to mix through a

mixing tip (Silicone

and polysulfideelastomers)

Polyether andpolyvinyl siloxane

benefit from their

shear thinningbehavior

Air bubbles in critical places?


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p

Smart syringing

keep the syringe tip inthe expressed materialduring syringing.

start syringing from the

most difficult areausually the disto-lingual.

use a three in one syringeto blow the light body

evenly over thepreparation

Voids


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Poorly adapted tray

Inadequate drying ofteeth

Premature syringing ofimpression material intra-orally prior to seating thetray

Salivary contamination ofthe syringed material.

management

Adequate wetting byimpression material

Tray must effectivelyconstrain theimpressionAdequate drying

U i i i l


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Unset impression material

Contamination of the impression by ingredientsof latex rubber gloves, which poison thechoroplatinic acid catalyst of addition silicones

Retraction solutions have not been shown toeffect impression setting significantly

de Camargo L M, et al. J Prosthet Dent 1993.

I i i i


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Impression inaccuracies

Invisible impression flaws,

resulting in an apparently good fit of therestoration on the die but a poor fit on the

tooth, may also occur because of:

Tray and impression recoil

Detachment of impression from tray

Permanent deformation

Tray and impression Recoil


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Impression

On tray removal, tray walls rebound

Dies andcastings whichare undersizedbuccolingually.

Tray and impression RecoilImpression

Impression TrayConsiderable forceto seat the puttyimpression

stresses

outward flexion of the tray wall

Rigid traysSpacing

management

Influence of tray material


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y

Metal and rigid plasticstock trays give greateraccuracy in theputty/wash silicone twinmix impressiontechnique compared withflexible plastic ones.

2008.Carrotte PV et al, J Prosthet Dent

Influence of tray material


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Gordon GE et al, J Prosthet Dent. 2003

Stock plastic tray generally producecasts with lower accuracy thancustom-made trays of acrylic resinand the thermoplastic material.


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Authors demonstrated that plastic stock trays

are convenient but whilst unreliable withputty-wash, they can produce accurate resultswith a combination of heavy and light bodied

addition silicones in a single step technique.

Wassell R Wand Ibbetson R,J Prosthet Dent 1991.

Abuasi H.Accuracy of polyvinyl siloxane

impressions. [PhD]. University of

Newcastle upon Tyne, 1993.

Abuasi H A, Wassell R W..Eur J Prosthodont

Restor Dent 1994


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Wassel et al, state that special trays are onlyneeded for heavy light bodied addition siliconeimpressions where stock trays are a poor fit.

British dental journal, 2002.British dental journal, 2002.

Management of Distortion During Tray


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g g yRemoval

Impression

Impression Tray

VERYFAST

(SNAP)

Strain rate sensitive elastomers

Fast removal

Slow removal

If the stress is applied quickly, then all the energy is stored elastically

and the material will not undergo plastic deformation.

However, some time is required for completeelastic recovery.

stort on me e ate to ett ngReaction


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Reaction

VPS P Eth PS, C Silicone100

log TIME (minutes)

REACTION

CO

NVERSION

(%)

Continue to react, shrink and distort after removalOnce the impression is clinically set (whichcorresponds to about 50% or greater reactionconversion), the impression tray can beremoved with a SNAP.


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Balancing out the effect of time for elastic

recovery and potential problems with

continued shrinkage.

Stick to the rule of waiting 20-30 minutes

before pouring.

Detachment of impression


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from tray

proper use of adhesive and having a tray withadequate perforations

allow time for the adhesives solvent to

evaporate and for adequate bond strength todevelop.

Where a special tray is made it is important thatthe wax spacer does not come into contact with

the tray acrylic; contamination will reduce thestrength of the adhesive bond.


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CLASSIFICATION

According to the impression

mixing methods

Hand mixing

Auto mixing

Machine mixing

Auto mix Technique


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-Impression material (Addition silicon) in prepackaged

cartridges with a disposable mixing tip attached.

The cartridge is inserted in a gun-like device, and the base

and catalyst are extruded into the mixing tip, where mixing

occurs as they progress to the end of the tip.

-The homogeneously incorporated material can be directly

placed on the prepared tooth and impression tray.

q

Advantage:1-Elimination of hand mixing

2- Fewer voids in the impression

3-Proper ratio

4-Reduced mixing time

5-Less contamination


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An alternative method for improving polyether and

addition silicon impression mixing is to use a machinemixer.

This system is convenient and produces void-free

impressions.

Machine Mixing Technique

EVALUATION of IMPRESSION


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EVALUATION of IMPRESSION

1. The impression material been properly mixed. An

impression that contains visible streaks of base or catalystmaterial should be rejected.

2. Impression material should be firmly attached to the tray

and not separated from the tray

3. No voids, folds in the preparation margin These

should have been avoided by careful technique.

4. NO part of tray is shown through the impression .

5. No interproximal tearing of the impression.

Disinfection


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Disinfection is an essential step for preventing

cross-infection for laboratory personnel.After being removed from the patient's mouth, the

impression is immediately

1-Rinsed with tap water2- Dried with an air syringe.

3-Suitable chemicals should be used, such as

Glutaraldehydesolutions (2% )orIodophoror

Chlorinecompound (1:10 dilution) orEthanol

sprays and stored in plastic bag.

The recommended procedures for the


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p

impression material


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THANKS

Documents

04 Impression Materials 2013