Impression Materials

Question 1

2 major categories of impression material:

Answer 1

• inelastic (rigid)
• elastic (flexibile)

Question 2

When did we use to use inelastic impressions specifically plaster?

Answer 2

• for edentulous patients
• ZOE is still used for cement
• compound is still used for border molding

Question 3

What are the 2 types of elastic impression materials?

Answer 3

• hydrocolloids (mainly use irreversible)
• elastomers (polysulfide, condensation silicone, addition silicone, polyether)

Question 4

What are the 2 elastomers impression material that don’t have byproducts?

Answer 4

• addition silicone
• polyether

Question 5

Do you dispense by equal lengths of equal volumes of impression material?

Answer 5

equal lengths

Question 6

Polysulfide chemistry reaction:

Answer 6

condensation reaction
- byproduct: water

Question 7

Benefit of Polysulfide impression material:

Answer 7

• manipulation time is long
• it sets in 10-20 minutes

Question 8

Composition of Polysulfide:

Answer 8

• base paste: polysulfide polymer, fillers
• accelerator paste:lead dioxide, sulfur (made bad smelling)

Question 9

Lead free options of Polysulfide:

Answer 9

omniflex and coe flex

Question 10

Composition of condensation silicones:

Answer 10

• base paste: dimethyl siloxane with reactive terminal hydroxyl groups (byproduct produced), fillers
• accelerator paste: tin octoate and an alkyl silicate

Question 11

Properties of Polysulfide:

Answer 11

• unpleasant odor (from sulfur)
• stains clothing
• extremely viscous/sticky
• hydrophobic

Question 12

Properties of condensation silicones:

Answer 12

• almost odorless
• variety of colors
• hydrophobic

Question 13

Chemistry of condensation silicones:

Answer 13

condensation rxn
- byproduct: alcohol

Question 14

Another name for addition silicones:

Answer 14

polyvinyl siloxane or vinyl polysiloxane

Question 15

What dental material has a composition with a base that has low molecular weight polymer with silane groups (-Si-H)?

Answer 15

addition silicones

Question 16

What do fillers do?

Answer 16

• more filler=thicker viscosity
• more filler= lesser contraction (more accurate)
• more filler= less detail

Question 17

Accelerator/catalyst for addition silicones:

Answer 17

chloroplatini acid catalyst

Question 18

What is seen in addition silicones to help with less bubble formation?

Answer 18

• palladium= it is a hydrogen absorber and hydrogen is what causes the bubbles

Question 19

Are addition silicones hydrophilic or phobic?

Answer 19

hydrophilic!
- different than polysulfudes and condensation silicones

Question 20

which consistency has the least and most filler?

Answer 20

• light (least amount of filler) < regular< heavy < putty (most amount of filler)

Question 21

How is addition silicones dispensed and mixed?

Answer 21

• mixed in cartridge and dispenses in gun
• more accurate and not wasting much material (only waste in mixing tube)

Question 22

How does the heavy wash/1 stage impression work?

Answer 22

• heavy body in tray
• wash material or light body around tooth

Question 23

How does putty wash/2 stage impression work?

Answer 23

• first, putty impression before prepping teeth
• then add heavy body in tray and light body around teeth
• better detail in all the teeth

Question 24

Addition silicone properties:

Answer 24

• almost odorless
• naturally hydrophobic (catalyst inside to change it though)

Question 25

Addition silicone setting reaction:

Answer 25

- rapid working time: 1-2 minutes setting time: 4-5 minutes

Question 26

Chain lengthen increases

Answer 26

viscosity

Question 27

Chain cross-linking increases

Answer 27

elasticity

Question 28

Which impression material used to have a catalyst that would cause a reaction?

Answer 28

Polyether- benzene was in it that caused reaction. eliminated now

Question 29

Which impression materials have an addition reaction with no by product?

Answer 29

- addition silicones - polyether

Question 30

A newer material that gets good properties from both addition silicone and polyether

Answer 30

vinyl polyether silicone

Question 31

Properties of vinyl polyether silicone:

Answer 31

- intrinsically hydrophilic - good flow - low contact angle (10 degrees/ polyether is 70 degrees) - working time: 2 minutes - setting time: 3.5 minutes - easier removal than polyether with increased flexibility - high tear strength (stretches out rather than tears)

Question 32

Which material are easier to mix due to low initial viscosity?

Answer 32

silicones - but means they set quicker

Question 33

Which have the most rapid setting function of time?

Answer 33

- addition silicone -polyether (due to low viscosity)

Question 34

Decreasing viscosity will _______ shear rate

Answer 34

increase

Question 35

Words for impression material thinning out when applying force:

Answer 35

shear thinning, pseudo plastic, thixotropic

Question 36

Working/setting times in order:

Answer 36

polysulfide (longest) > silicones > polyethers (shortest)

Question 37

Working/setting times are shortened by:

Answer 37

increasing temp and humidity - so will set faster in patients mouth

Question 38

Shrinkage of impression material due to:

Answer 38

- evaporation of byproducts - thermal contraction - rearrangement of bonds during polymerization

Question 39

Dimensional changes/shrinkage in order of material:

Answer 39

addition silicone (smallest) < polyethers and polysulfide < condensation silicone (largest)

Question 40

Shrinkage occurs towards the ____

Answer 40

tray

Question 41

Which materials can affect the dimensional change by absorbing water?

Answer 41

- polyether and hydrophilic addition silicone - don't wrap up in wet paper towel because then it will swell and cast will be smaller

Question 41

Order of permanent deformation/elastic recovery of impression material:

Answer 41

addition silicone (best recovery)> condensation silicone> polyether> polysulfide

Question 42

Order of flexibility/strain of impression materials:

Answer 42

polyether (stiffest) > addition silicone> condensation silicone> polysulfide (more flexible)

Question 43

Which material have the lowest flow?

Answer 43

silicones and polyether

Question 44

Order of hardness of impression materials:

Answer 44

polyether (hardest > addition silicone > condensation silicone > polysulfide

Question 45

Order of tear strength of impression materials:

Answer 45

polysulfide (highest resistance) > silicones > polyether