Impression Materials

Front 1

Alginate

Back 1

Irreversible Hydrocolloid
Alginic acid is reacted with calcium sulfate dihydrate and water to form a calcium alginic gel and potassium sulfate

Front 2

Agar

Back 2

Reversible Hydrocolloid
Composed of linear carb chains, similar to alginic acid without carboxylic acid groups
Liquefies at 70-100 celcius
Gels at 30-50 celcius
Reversible because you can heat and cool it

Front 3

Polysulfides

Back 3

Use for removal of partial dentures
Reactive terminal mercaptan (-SH) groups and reactive sulfur groups extended from within the polymer allow cross linking during polymerization

Front 4

Advantages of Polysulfides

Back 4

Low cost (compared to silicones and polyethers)
Long working time
High tear strength
High flexibility
Good detail reproduction

Front 5

Disadvantages of Polysulfides

Back 5

Porr dimensional stability (water by-product, pour within 1 hr, Single pour)
Custom Trays
Messy (paste-paste mix, bad odor, may stain clothing)
Long setting time

Front 6

Polysiloxane (Condensation silicones)

Back 6

Curing involves tri- or tetra-functional alkyl silicate crosslinking hydroxyl terminated silicone polymers by condensation rxns.
A catalyst (metal organic ester) is needed.
Loss of rxn by-products (ethanol) resulted in significant dimension changes over time

Front 7

Polyvinyl Siloxanes (addition silicones)

Back 7

Base contains filler particles, vinyl dimethly polydimethyl siloxanes, polymethyl hydrogen siloxane (-SH)
Accelerator contains filler vinyl dimethyl polydimethyl siloxanes and chloroplatinic acid (catalyst)
Moisture of impurities (silanol) can react w hydride and yield hydrogen gas, whihc can be eliminated through absorption by adding palladium or platinum salts

Front 8

Advantages of Polyvinylsiloxanes (addition silicones)

Back 8

Highly accurate
High dimensional stability
Stock or custom trays
Multiple casts
Easy to mix
Pleasant odor

Front 9

Disadvantages of Polyvinylsiloxanes (addition silicones)

Back 9

Expensive
Sulfur inhibits set (latex gloves, Fe and Al sulfate retraction solution)
Short working time
Lower tear strength

Front 10

Polyethers

Back 10

Base is a low molecular weight polyether with a reactive imine ring
Polymerization occurs via cationic polymerization opening of the active imine ring
Resulting polymer is a tetrahydrofuran/ethylene oxide copolymer
It can absorb water when immersed in water

Front 11

Polyethers

Back 11

Another class is based on alkoxysilane terminated polyether
Polymerization occurs via condensation of alkoxysilane group
System with alkoxysilane claims to be free of water absorption

Front 12

Advantages of Polyethers

Back 12

Highly accurate
Good dimensional stability
Stock or custom trays
Good surfae detail
Pour within one week (keep dry)
Multiple casts
Good wettability

Front 13

Disadvantages of Polyethers

Back 13

Expensive
Short working time
Rigid (difficult to remove from undercuts)
Bitter taste
Low tear resistance
Absorbs water (changes dimension)

Front 14

Surface Wettability

Back 14

Impression materials can be classified as readily wettable by gypsum (hydrophilic) or resistant to wetting (hydrophobic)

Front 15

Which materials are hydrophilic and easiest to pour?

Back 15

Irreversible hydrocolloid (Alginate)
Reversible hydrocolloid
Polyether

Front 16

Wettability by water

Back 16

hydrocolloids > polyether > hydrophilic addition silicone > polysulfide > hydrophobic addition silicone (condensation silicone)

Front 17

Higher contact angle

Back 17

= greater probability of air entrapment (bubbles) during pouring
= More readily repelled by hemorrhage or other sources of moisture

Front 18

Working/Setting time of Polysulfides

Back 18

Working = 3-6 minutes
Setting = 6-10 minutes

Front 19

Working/Setting time of Addition Silicones

Back 19

Working = 2 min
setting = 4-6 min

Front 20

Working/Setting time of Polyethers

Back 20

working = 2-3 min
setting = 3-5 min

Front 21

Best working/setting?

Back 21

Use Polysulfides or Addition Silicones for multiple preps.
Polyethers can be utilized when rapid sets are required

Front 22

Tear Strength

Back 22

maximum load divided by the thickness of the specimen
&uarr as viscosity &uarr

Front 23

What has greatest tear strength?

Back 23

Light-body Polysulfide
Polysulfides use when multiple subgingival areas are present

Front 24

What is the Stiffest material?

Back 24

Polyethers - require care in patients with long teeth or tissue undercuts - consider low viscosity materials

Front 25

Impression Tray

Back 25

be rigid
dimensionally stable
allow uniform layer of impression material
retain impression material
correct extenstion
distinct seating

Front 26

Thixotropic

Back 26

a material that becomes more fluid when the shear rate is increased by deforming or disturbing it
This property allows making impression with Monophase (single viscosity)

Front 27

Thixotropic Agent

Back 27

Used to increase viscosity of material to reduce slumping during processing

Front 28

Viscoelasticity

Back 28

material has viscous and elastic characteristics when undergoing deformation

Front 29

Fast Removal

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elastic property

Front 30

Slower Removal

Back 30

facilitates plastic deformation

Front 31

Polyvinylsilicone catalyst

Back 31

platinum salt

Front 32

Polyether catalyst

Back 32

aromatic sulfonate

Front 33

How much shrinkage occurs in first hour?

Back 33

half

Front 34

What material is most stable?

Back 34

Addition Silicone > Polyethers > Polysulfides

Use Addition Silicones when undercuts are present