ne may not get a chance to make a good first impression. But remember that the first impression is not the last chance to make a good impression

o

GOOD MORNiNG

ELASTIC Impression MATERIALS

ABHISHEK KAVLEKAR

C O N T E N T S

DefinitionClassification History

Reversible & Irreversible Hydrocolloid i)Composition ii)Gelation Process iii)Impression Making iv)Properties v)Advantages-Disadvantages vi)Uses

viii)Disinfection xi)Common failures and causes.

Laminate techniqueDuplicating materials

Elastomeric Impression Materials-Polysulfide, Silicones and Polyetheri)Compositionii)Setting Reactioniii)Advantages-Disadvantagesiv)Impression techniquesv)Shelf lifevi)Disinfectionvii)Effects of mishandling

C O N T E N T S

Visible Light Cured Polyether Urethane dimethacrylateTissue Conditioners

Summary

Conclusion

References

elastic : susceptible to being stretched, compressed, or distorted and then tending to resume the original shape

elastomeric impression material: a group of flexible chemical polymers, which are either chemically or physically cross-linked. Generally, they can be easily stretched and rapidly recover their original dimensions when applied stresses are released.

Glossary of prosthodontic terms

Impression materials

Rigid

Impression plaster

Zinc Oxide Eugenol

Impression compound

Impression waxes

Elastic

Hydrocolloid

Elastomers

Reversible hydrocolloi

dIrreversible

hydrocolloi

dPolysulfid

es

Silicones

Polyether

s

7

Hydrocolloid Polysulfide Polyether Hydrophilic Ad

silicone ↓ ↓ ↓ ↓

I 1920 I 1930 I 1 940 I 1950 I 1960 I 1970 I 1980 I1990 I 2000 ↑ ↑ Condensation Addition silicone silicone

HISTORY

COLLOIDS

A solid, liquid or gaseous substance made up of large molecules or masses of smaller molecules that remain in suspension in a surrounding continous medium of diffrent matter*

A colloid that contains water as the dispersion phase is called as HYDROCOLLOID*

*Anusavice KJ: Philips’ Science of Dental Materials. 11th Edition

REVERSIBLE HYDROCOLLOIDS

Organic hydrophillic colloid extracted from SEAWEED. It chiefly contains agarose and agaropectin.

Introduced by Alphous Poller of Vienna” in 1925.

Chemically it is a sulfuric ester of galactan complex.

The agar used in dentistry is supplied in the following forms-1) Tray material2) Syringe material3) Agar for duplication

COMPOSITIONComponent Function Composition(

%)Agar Brush Heap

structure13 – 17

Borate Strength 0.2 – 0.5

Potassium Sulfate Gypsum hardener 1.0 – 2.0

Diatomeceous earth, Wax, Silica, clay etc

Filler 0.5 – 1.0

Thixotropic materials Thickener 0.3 – 0.5

Water Reaction medium Balance 84%

Alkylbenzoates Perservative 0.1

Thymol Bactericidal trace

Glycerine Placticizer trace

GELATION PROCESS

The setting of reversible hydrocolloid is called gelation

It is a temprature induced solidification process involving phase change from sol to gel.

Gel Liquefaction temperature

Sol Gelation temperature

Gel

70-100ºC

37-50ºC

Hysteresis

LIQUEFACTION

• 100°C• Minimum of

10 minutes.• Propylene

glycol

STORAGE

• 65°C• Several days

TEMPERING

• ~45°C• 3 to 10 min• Never for

syringe material

PREPARATION AND CONDITIONING OF AGAR

•Just before completion of tempering of tray material the syringe material is taken from the storage compartment and applied to the base of preparation•Water soaked outer layer of the tray hydrocolloid is removed • Tray is seated with light pressure & held with light force•Gelation is accelerated by circulating cool water (approximately 18 to 21°C) through the tray for 3 to 5 minutes.

IMPRESSION MAKING

Triple tray technique

At the appropriate viscosity it is very easy for the patient to “bite through” the material

Hence ,the triple tray technique is commonly used with reversible hydrocolloids.

With this ,one impression records the structures of maxillary and mandibular arches as well as occlusal relationship.

Wet fi eld technique

Area to be recorded is flooded with warm water

Syringe agar material – is quickly & liberally syringed over prepared tooth

Tray agar placed over the syringed agar

PROPERTIES OF AGAR

• Greater than 96.5% (permanent deformation less than 3.5%) after the material is compressed 20% for 1 second

• Tray types have elastic recovery of about 99%

Elastic Recovery

• The ANSI/ADA Specification 11 requirement for flexibility allows a range of 4 to 15%

Flexibility

• Compressive strength is 0.8 MPa• Tear strength is 0.8 to 0.9 N/mm.• The ANSI/ADA Specification requirement: 0.75 N/mm

Strength

• If the material is held rigidly in the tray, the impression material shrinks toward the center of its mass

• Rapid cooling may cause a concentration of stresses near the tray where the gelation first takes place

Distortion during Gelation

• It must be sufficiently viscous so that it will not flow out of the tray

• It must not be so great that it will not readily penetrate every detail of the teeth and the soft tissues

Viscosity of the Sol

ADVANTAGES

Good elastic properties.

Good recovery from distortion.

Accurate dies can be prepared.

Palatable and well tolerated by the patient.

Can be used for duplicating models.

As it is not hydrophobic, it gives a good model surface.

DISADVANTAGES

Extensive and expensive equipment.

Dimensional instability.

Pain and thermal shock.

Cannot be electroplated.

Tears easily.

Disinfection.

21

USES

1. Impressions for fixed prosthesis.

2. Duplicating material.

3. Tissue conditioning material.

IRREVERSIBLE HYDROCOLLOIDS

•Developed as a substitute for agar during World War II

•E.C.C. Stanford, a Scottish chemist, discovered alginates from from brown seaweed (algae) also called algin in the 1880s

40 yrs later, “S. William Wilding” received the patent for alginate as impression material.

It is a linear polymer of anhydro --D mannuronic acid” of high molecular weight.

composition

Component Function Wt%

Potassium alginate Soluble alginate 15

Calcium sulfate

dihydrate

Reactor 16

Zinc oxide Filler particles 4

Potassium Titanium

fluoride

Accelerator 3

Diatomaceous earth Filler Particles 60

Sodium phosphate Retarder 2

Gelation process

K2nAlg + nCaSO4 nK2SO4 + CanAlg

2Na3PO4 + 3CaSO4 Ca3(PO4)2 + 3Na2SO4

25

26*Lemon JC et al ( J Prosthet Dent: 2003 Sep;90(3):276-81.

Control of setting time

Best regulated by the amount of retarder added by the manufacturer.

Clinician can safely influence the setting time by altering the temprature of water .

A minute reduction in setting time occurs for each 10°C of temprature increase.

Addition of 1-8 drops of sodium phosphate*

Never change the water powder ratio

manipulation

The measured powder is sifted into premeasured water that has already been poured in clean rubber bowl.

If the powder is placed first ,penentration of water to bottom of bowl is inhibited.

In a vigrous figure of 8 motion the mix is swipped or stropped against the side of bowl to press out air bubbles

Frey G, Lu H, Powers J (J Prost: 2005 Dec;14(4):221-5)

Concluded that mechanical mixer improved elastic recovery and compressive strength of the alginate impression materials and had no effect on strain in compression and tear energy. A mechanical mixer facilitates the mixing of alginate impression materials and improves some mechanical properties.

Mechanical mixer

IMPRESSION MAKING

Select a perforated tray

Mixing and loading

Making the impression

Wait for 3mins

Remove impression rapidly in a single jerk

Cut off the excess

Morris et al ( J Prosthet Dent 1983,49: 328-330)

• Demonstrated that smoothing the surface of the mixed alginate with a wet finger, prior to making the impression, consistently resulted in fewer bubbles on the surface of casts.

properties

Mixing time

Setting time

Working time

1. Fast set: 45 sec.2. Regular set: 60 sec.

1. Fast set: 1.25 to 2 min.2. Regular set: 3 to 4.5 min.

1. Fast set: 1.5 to 3 min.2. Regular set: 3 to 4.5 min.

31

Elastic recovery Greater than 95% when the material is compressed 20% for 5 seconds.

Flexibility Range of 10 to 20% at a stress of 1000g/cm2

Strength Compressive strength–at least

0.35MPA

Tear strength – 0.37 to 0.69 MPa

32

Factors aff ecting strength

Too much or too little water used for mixing

Insufficient spatulation

Over mixing

Failure of ingredients to dissolve sufficientlyBreaks up the calcium alginate gel network

Results in weakened final gel, making it less elastic

Accuracy

1. Increase in concentration of alginate to make the material more accurate

2. Roughness of the impression surface is sufficient to cause distortion

3. Sufficiently accurate to be used for making impressions for removable partial denture prosthesis

1. Model should be poured as soon as possible

2. Stored in 100% relative humidity in a plastic bag or wrapped in a damp paper towel

3. Greater chance of distortion the longer the impression is stored

Dimensional stability

34

Easy to mix and manipulate

Minimum requirement of equipment

Accuracy (if properly handled)

Low cost

Comfortable to the patient

Hygienic (as fresh material is used for each impression)

ADVANTAGES 35

Not accurate for crown and bridge impressions

Cannot be electroplated

Distortion occurs easily

Poor dimensional stability

Poor tear strength

DISADVANTAGES

36

uses

1. Complete and removable denture prosthesis

2. Study models and working casts

3. Duplicating models

37

LAMINATE TECHNIQUE

Syringe agar

Gels by chemical reaction

Gels by means of contact with the cool alginate

38

DUPLICATING MATERIAL

39

ADA specification 20 -Type I (thermo reversible)Type II (nonreversible)

Hydrocolloids are popular and have the same composition as the impression materials, but their water content is higher, consequently agar or alginate content is lower

MODIFIED ALGINATES

1. In the form of a sol, containing the water. A reactor of plaster of Paris is supplied separately.

2. Two paste system, one containing the alginate sol, and second containing the calcium reactor. These materials are said to contain silicone and have superior tear resistance.

3. Lee YK et al in this study concluded that addition of NaF in an alginate impression material may result in effective release of fluoride without deteriorating the properties of material itself*

*J. Mater Sci Mater Med :

2004 Mar;15(3):219-24)

40

These alginates change color during manipulation to give a clear indication of mixing time, loading into mouth & setting of the material

They contain acid/base indicators that are responsible for change in color at different critical points due to changes in pH that occur during setting

Three phases of chromatic alginates are – RED PHASE: MIXING TIME

ORANGE PHASE: WORKING TIME

YELLOW PHASE: TIME IN THE MOUTH

41

Chromatic alginates

DISINFECTIONImpression is rinsed

Disinfectant sprayed liberally

W

r

a

p

p

e

d

i

n

d

i

s

i

n

f

e

c

t

a

n

t

s

o

a

k

e

d

p

a

p

e

r

t

o

w

e

l

P

l

a

c

e

d

i

n

a

s

e

a

l

e

d

p

l

a

s

ti

c

b

a

g

f

o

r

1

0

m

i

n

u

t

e

s

Wrapped impression is removed, rinsed and poured

Household bleach

Iodophor

Synthetic phenols

42

STORAGE OF IMPRESSION

•Shorter storage time of hydrocolloid impressions before pouring is desirable. •Agar Impressions can be stored up to 1 hour in 100% humidity or in storage media like 2% potassium sulfate*

•If irreversible hydrocolloid impression pouring is to be delayed up to three hrs, then it should be wrapped with a wet towel and poured within 3 hrs, as this did not appear to affect their accuracy significantly.**

*J Prosthet Dent 2001:86(3); 244-50.**Saudi Dental Journal 2002,:14(3).

Common fa i l u res and causes .

Agar

Inadequate boiling

Storage temperature too low

Storage time too

long

Alginate

Improper mixing

Prolonged mixing

Excessive gelationWater

powder ratio too

low

Grainy material

AgarWater-soaked

tray surface material

not removedPremature gelation of either

Alginate

Not applicabl

e

Separation of tray and syringe materials

45

Tearing

Agar

Inadequate bulk

Premature removal from mouth

Syringe material partially gelled when tray was

seated

Alginate

Inadequate bulk

Moisture contamination

Premature removal from mouth

Prolonged mixing46

Agar

Inadequate cleansing

Excess water

Improper manipulation of stone

Air drying the impression before pouring

Alginate

Inadequate cleansing

Excess water left on the impression

Premature removal

Model left in impression too long

Improper manipulation of stone

47

Rough or chalky stone model

Agar

Impression not poured immediately

Movement of tray during gelation

Premature removal from mouth

Improper removal from mouth

Use of ice water during initial

stages of gelation

Alginate

Impression not poured immediately

Movement of tray during gelation

Premature removal from mouth

Improper removal from mouth

Separation of alginate from the

tray 48

Distortion

Agar

Gelation of syringe

material- preventing flow

Alginate

Undue gelation preventing flow

Air incorporated during mixing

Agar

Material too cold

Alginate

Moisture or debris on

tissue

49

Irregularly shaped voids

External bubbles

Elastomeric impression materials

50

Chemically, there are 3 kinds of elastomers

1)Polysulfides2)Silicone a. Additionb. condensation3) Polyethers

CLASSIFICATIONCurrent ADA specification 19 recognizes 3 types of elastomeric

materialsThis classification is based on selected elastic properties &

dimensional changeType Max

permanent deformation

Max flow in compression

Max dimensional change in 24

hrs

I 2.5 0.5 -0.5

II 2.5 0.5 -1.0

III 5.5 2.0 -0.5

51

Type Decriptionconsistency

Consistency test discDiameter(mm)

min max

0 Very high(putty) - 35

1 High(heavy bodied) - 35

2 Medium(medium bodied)

31 41

3 Low(light bodied) 36 -

According to ISO 4823 the method of classification according to consistency is as following-

polysulfi des

First synthetic elastomeric impression material

Also known as MERCAPTAN or THIOKOL

-Mode of supplyCollapsible tubesOne labeled Base paste and Other labeled Accelerator paste

-Consistencies Light body(syringe or

wash) Medium body (regular) Heavy body

1950

composition

Polysulfide polymer - 80 to 85%

Fillers - 16 to 18%Titanium dioxide, lithopone, zinc sulfate,

copper carbonate or silica

Dibutyl phthalate-plasticizerSulfur (0.5%) – accelerator

Lead dioxide; 60 to 68%

Oleic/stearic acidRetarder

Deodorants

BASE PASTE

REACTOR PASTE

Chain lengthening by oxidation of terminal –SH groups

Cross linking by oxidation of pendant –SH groups

Setting reaction

Polysulfide polymer

Lead dioxid

e

Polysulfide

water

∆ 3 to 4°C 54

Long working time

Good tear strength

Radiopaque

Good reproduction of surface detail

High flexibility

Lower cost

Need to use custom made trays

Bad odor

Tendency to run down patient’s throat

Stains clothing & messy to work with

Must be poured within 1 hour

Hydrophobic so impression area has to be dry

ADVANTAGES DISADVANTAGES

55

Condensation silicones

Mode of supply Collapsible tubes Base paste and Accelerator paste / liquid Putty is supplied in jars

Consistencies Light body (syringe or wash) Putty

Also known as conventional silicones

1955

composition

Polydimethyl siloxaneFillers; 16 to 18%

Calcium carbonate or silica

Tetra-ethyl Orthosilicate- reactor

Stannous octoate - catalyst

BASE PASTE

REACTOR PASTE

Tetra-ethyl orthosilicate

Dimethylsiloxane

Silicone rubber

Ethyl alcohol

Stannous octate

∆ 1°C

Cross linkage between Orthoethyl silicate and the terminal hydroxyl group of Dimethylsiloxane to form a 3 Dimensional network 58

SETTING REACTION

Clean, pleasant materials

Highly elastic

Putty-wash system improves accuracy

Inaccuracy due to shrinkage

Must be poured within 1 hour

Hydrophobic so impression area has to be dry

ADVANTAGES DISADVANTAGES

59

Addition silicones

Mode of supply Collapsible tubes Base paste and Accelerator paste Putty is supplied in jars

Consistencies Light body (syringe or

wash) Medium body (regular) Heavy body Putty

Also known as polyvinyl siloxane or vinyl polysiloxane

1975

60

composition

• Base paste

Poly methyl hydrogen siloxane

Other siloxane prepolymers

Fillers- Divinyl poly siloxane

• Reactor pastePlatinum salt: Catalyst

(chloroplatinic acid)

Palladium: Scavenger

Vinyl siloxane

Silane (hydride groups)

Silicone rubber

Platinum salt

The base polymer is terminated with vinyl groups and is cross linked with hydride groups 62

Setting reaction

Highly accurate

High dimensional stability

Recovery from deformation on removal is excellent

May be used with stock or custom trays

Can be poured after 1 week

Multiple pours are possible

Expensive – twice the cost of Polysulfides

More rigid than condensation & difficult to remove around undercutsModerate tear strength, making removal from sub-gingival areas riskySulfur in latex gloves and rubber dam inhibit polymerizationPouring of the stone should be delayed by 1-2 hrs, liberation of H2 gas

ADVANTAGES DISADVANTAGES

63

polyether1960s

Mode of supply Collapsible tubes Base paste Accelerator paste Third tube containing thinner may be suppliedConsistencies Light bodied(syringe or

wash) Medium bodied (regular) Heavy bodied

First elastomer to be developed primarily to function as an impression material

64

• Base paste

Poly ether polymer

Fillers; colloidal silica

Glycoether or phthalate; plasticizer

• Reactor paste

Alkyl – aromatic sulfonate ester; cross linking agent

Fillers and plasticizersOctyl phalate and 5% methyl

cellulose-thinning agents

COMPOSITION

The main chain is a copolymer of ethylene oxide and tetrahydrofuran.

Cross linking is brought about by thearomatic sulfonate ester via the imine end Groups.

66

SETTING REACTION

Polyether Sulfonate ester

Cross linked rubber

Pleasant mixing and ease of handling

More accurate than polysulfide and condensation silicone

Good surface detail reproduction

Easily poured in stone

If kept dry, will be dimensionally stable for up to 1 week

High cost

High stiffness

Bitter taste

Storage of impressions is critical

cannot be left in disinfectants for long

ADVANTAGES DISADVANTAGES

67

Manipulation methods

Hand mixing

Static auto mixing

Dynamic mechanical mixing

68

TRAY ADHESIVES

Silicones

PolysulfidesButyl rubberStyrene/acrylonitrileDissolved in volatile solvent such as chloroform or ketone

Hydrated silica forms ethyl silicate – bonds with the trayPolydimethyl siloxane – bonds with the rubber69

IMPRESSION TECHNIQUES

1)Multiple mix technique

2)Single viscosity technique

3)Putty wash technique

70

MULTIPLE MIX TECHNIQUE

Heavy and light body mixed simultaneously

light body loaded in syringe

Tray adhesive applied

Light body injected into prepared teeth

Heavy body loaded in the tray

Final impression

SINGLE VISCOSITY TECHNIQUE

Only one mix is made- Part of it is placed in the trayAnother portion is placed in syringe for injection

Medium viscosity of addition and polyether can be used.

PUTTY WASH TECHNIQUE

Preperation of stonecast & dies

All elastomers are compatible with gypsum products

Excellent dimensional stability of addition silicone and polyether makes it possible to construct 2 or 3 casts

Hydrophobic addition silicone – problem ????

74

Hydrophilized vinyl polysiloxane

• Surfactants are added to reduce the contact angle;

dilute solution of soap

• Most commonly used – non-ionic surfactants

oligoether or polyether substructureHydrophilic part

Silicone compatibleHydrophobic part

PVS

Diffusion – controlled transfer of surfactant molecules from PVS to

aqueous phase

Reduction in surface tension

Greater wettability

75

water

Hydrophilized vinyl polysiloxane

properties

Impression material

Mean working time Mean setting time

Polysulfide 6.0 4.3 16.0 12.5

Condensation silicone

3.3 2.5 11.0 8.9

Addition silicone 3.1 1.8 8.9 5.9

Polyether 3.3 2.3 9.0 8.3

23°C 37°C 23°C 37°C

78

WORKING AND SETTING TIMES

Temperature

Working and setting timeHumidity

Viscosity

Factors aff ecting working-setting time

Dimensional stability

1)Polymerization shrinkage2)Loss of by – product3)Thermal contraction from oral

temperature to room temperature4)Imbibition5)Incomplete recovery of deformation

Addition silicones-0.17%

Polyether-0.24%

Polysulfides-0.40%

Condensation silicones-0.60%

Dimensional change

Addition silicones

Polyether

PolysulfidesCondensation silicones

Permanent deformation

Addition silicones-0.17%

Polyether-0.24%

Polysulfides-0.40%

Condensation silicones

-0.60%

STIFFNESS

Addition silicones

Polyether

PolysulfidesCondensation silicones

TEAR STRNGTH

Addition silicones

0.01-.03%

Polyether0.03%

Polysulfides0.5-2%

Condensation silicones0.05-0.1%

FLOW

BIOCOMPATIBILITY

Probability of allergic reactions is lowPolysulfide has the lowest cell death count

Polyether has the highest cell death count ,toxicity and contact dermatitis among the class.

The most likely problem is lodgment of impression material in gingival sulcus resulting in severe inflammation,

Clinical consideration :

o Subgingival regions are very thin – material can tear

o Residual segment of impression material difficult

to detect radio opacity of polysulfide can help

o Severe gingival inflammation.

o Examine the gingival sulcus immediately after impression removal and also the impression for any evidence of tearing

87

Polysulfides –2 years

Condensation silicone – stannous octoate oxidizesOrthoethyl silicate is not stable in presence of tin ester

Addition silicone – 1 to 2 years

Polyether – Excellent shelf life; more than 2 years

StorageCool, dry environmentTubes always tightly sealedContainer closed

88

SHELF LIFE

DISINFECTIONMATERIAL DISINFECTANTS

PolysulfideSilicones(by immersion-not more than 30 min/spray)

2% Glutaraldehyde Chlorine compoundsIodophors Phenolics

Polyether Chlorine compounds Iodophors

Use disinfectant with short immersion time(less than 10 min) to avoid distortion(Polyether is hydrophilic)

89

• 1)Impression making• 2)Bite registration

– The material is fast setting.– There is no resistance to biting forces.– There is no odor or taste for the patient.– It gains dimensional stability over time.– It is convenient to use.

• 3)DuplicationPolyvinyl siloxane and polyether duplicating materials are superior in accuracy than agar reversible hydrocolloid duplicating materials. *

*Accuracy and reproducibility of reversible hydrocolloids versus elastomers duplicating materials Bahannan, S et al. The Saudi Dental Journal 1995:7( 1)

uses

Common failures

ROUGH OR UNEVEN SURFACE ON IMPRESSION

1. Incomplete polymerization cause by premature removal.

2. improper ratio or mixing of components

3. presence of oil or other organisms on the teeth

4. Too rapid polymerization from high humidity or temperature

5. Excessively high accelerator/base ratio

BUBBLES

1. Too rapid polymerization , preventing flow

2. Air incorporated during mixing

IRREGULAR SHAPED VOIDS

1. Moisture or debris on surface of teeth

ROUGH OR CHALKY STONE CAST

1. Inadequate cleaning of impression

2. Excess water or wetting agent left on surface of the impression

3. Premature removal of cast

4. Improper manipulation of stone

5. Failure to delay pour of addition silicone at least 20min

1. Lack of adhesion of rubber to the tray caused by not applying enough coats of adhesive

2. filling tray with material too soon after applying adhesive or using wrong adhesives

3. Lack of mechanical retention for those materials where adhesive is ineffective

4. Development of elastic properties in the material before tray is seated

5. Excessive bulk of material

DISTORTION

95

6. Insufficient relief for the reline material

7. Continued pressure against impression material that has been developed elastic properties

8. Movement of tray during polymerization

9. Premature removal from the mouth

10.Delay pouring of the polysulfide or condensation silicone impression

VISIBLE LIGHT CURED POLYETHER URETHANE

DIMETHACRYLATEIntroduced in early 1988 by Genesis & LD Caulk

1. Polyether urethane dimethacrylate – elastomer resin

2. Chloroquinone – photoinitiator3. Silicon dioxide – filler 0

Light body – syringe

Heavy body – tubes

Mode of supply

Composition

97

Manipulation 1. Loaded tray is seated in the mouth2. 8mm or larger diameter optical probe is placed in

the mouth below the tray3. Blue light is activated for 3 minutes4. Impressions can be poured immediately or stored

up to 2 weeks

1. Long working time and short setting time.

2. Blue light is used for curing with transparent impression trays.

3. Tear strength – 6000 to 7500 gm/cm2 (Highest among elastomers)

4. Other properties are similar to addition silicones

Properties

1. Special transparent trays 2. Difficult to cure in remote

area

Disadvantages Advantages

1. Controlled working time 2. Excellent properties 3. Ease of cold

disinfection without loss of quality.

4. The impression material is also compatible with gypsum and silver or copper metallizing baths

99

 It combines the benefits of polyether and vinyl polysiloxane impression materials. The pleasant tasting hybrid impression material purportedly has hydrophilic properties, high tear strength, excellent dimensional accuracy and resistance to deformation. It is available in two setting times (fast and regular) and four viscosities (putty, heavy body, monophase and light body)

VINYL SILOXANTHER

TISSUE CONDITIONERS

Soft elastomers Composed of powder that contains poly(ethyl methacryalte) and liquid that contains an aromatic ester – ethyl alcohol mixture (up to 30%) Within few days they become stiffer as a result of loss of alcohol so need to be replaced every 3 days

USES1. Tissue conditioners for irritated mucosa 2. Temporary soft liners3. Functional impression materials

101

PROPERTIES 1. Hydrophilic; accurate impression in presence of saliva

2. Dimensional stability is fair

3. Low rigidity , Low tear strength

4. Adhere to themselves and are excellent for border molding and correctable impression technique

5. Do not distort from water absorption, but they distort easily when exposed to alcohol based disinfectants

6. Properties which make s the material effective are-Viscous behaviour-allow adaptation to irritated denture

bearing mucosa for several daysViscoelasticity which cushions the cyclic forces of

mastication and bruxism

•Tissue conditioners should not be cleaned by scrubbing with a hard brush in order to prevent tearing of the material. The use of soft brush under running water is recommended. •The greatest virtue of tissue conditioners is their versatility and ease of use. •The biggest flaw is that they are also misused

SUMMARY

Elastomers since their introduction have revolutionised the art of impression making hence allowing the operator to provide acuurate fitting restorations

Addition silicones and polyethers account for major portion of the current practice.

Condensation silicones, Polysulfides and irreversible hydrocolloids – more sensitive with respect to handling considerations , mix-and-pour techniques, which may affect accuracy.

104

CONCLUSIONThe understanding of basic knowledge of the impression materials and their behavior during handling are important for their use in the oral environment and clinical success.

The selection of the material best suited for a particular clinical situation and technique rests with the operator.

references

• Anusavice KJ: Philips’ Science of Dental Materials. 11th Edition. Elsevier:S Louis;2003

• William J. O’Brien: Dental Materials Properties and Selection

• Craig RG,Restorative Dental Materials.9th Edition. Mosby:St Louis;1993

• Impression materials: A comparative review of impression materials most commonly used in restorative dentistry DCNA 2007;51(3):629-642

• McCabe JF, Walls AW:Applied Dental Materials.9th Edition.Blackwell Publishing:Singapore;2008

• Kowdi MS, Patil SG.Prep manual for undergraduates: Dental materials.

• Schleier PE, et al The effect of storage time on the accuracy and dimensional stability of reversible hydrocolloid materials. J Prosthet Dent 2001 ;86(3):244-50.

• Jamani KD The effect of pouring time and storage condition on the accuracy of irreversible hydrocolloid impression. Saudi Dental Journal 2002:14(3).

• Woody et al Hydocolloids: A comparative study.J Am Dent Assoc 1977,94:501-504

• Lemon JC et al Facial moulage:The effevt of a retarder on compressive strength and working and setting times of irreversibe hydrocolliid impression material. J Prosthet Dent: 2003 ;90(3):276-81.

references

• Lee YK et al in this Effect of fluoride addition on the properties of dental alginate impression materials study J. Mater Sci Mater Med : 2004 ;15(3):219-24• Morris et al Effect on surface detail of casts when irreversible hydrocolloid was wetted before impression making.J Prosthet Dent 1983,49: 328-330• Bahannan, S et al Accuracy and reproducibility of reversible hydrocolloids versus elastomers duplicating materials.The Saudi Dental Journal 1995:7( 1)• Stackhouse, J.A., Jr., Harris, W.T., Mansour, R.M. and Von Hagen, S. A study of bubbles in a rubber elastomer manipulated under clinical conditions. J Prosthet Dent 57:591-596, 1987

references

Thank you

ELASTIC Impression MATERIALS

ABHISHEK KAVLEKAR