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Indirect Exam 2 > Impression Materials > Flashcards

Impression Materials Flashcards

1
Q

2 major categories of impression material:

A
  • inelastic (rigid)
  • elastic (flexibile)
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2
Q

When did we use to use inelastic impressions specifically plaster?

A
  • for edentulous patients
  • ZOE is still used for cement
  • compound is still used for border molding
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3
Q

What are the 2 types of elastic impression materials?

A
  • hydrocolloids (mainly use irreversible)
  • elastomers (polysulfide, condensation silicone, addition silicone, polyether)
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4
Q

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

A
  • addition silicone
  • polyether
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5
Q

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

A

equal lengths

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6
Q

Polysulfide chemistry reaction:

A

condensation reaction
- byproduct: water

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7
Q

Benefit of Polysulfide impression material:

A
  • manipulation time is long
  • it sets in 10-20 minutes
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8
Q

Composition of Polysulfide:

A
  • base paste: polysulfide polymer, fillers
  • accelerator paste:lead dioxide, sulfur (made bad smelling)
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9
Q

Lead free options of Polysulfide:

A

omniflex and coe flex

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10
Q

Composition of condensation silicones:

A
  • base paste: dimethyl siloxane with reactive terminal hydroxyl groups (byproduct produced), fillers
  • accelerator paste: tin octoate and an alkyl silicate
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11
Q

Properties of Polysulfide:

A
  • unpleasant odor (from sulfur)
  • stains clothing
  • extremely viscous/sticky
  • hydrophobic
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12
Q

Properties of condensation silicones:

A
  • almost odorless
  • variety of colors
  • hydrophobic
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13
Q

Chemistry of condensation silicones:

A

condensation rxn
- byproduct: alcohol

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14
Q

Another name for addition silicones:

A

polyvinyl siloxane or vinyl polysiloxane

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15
Q

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

A

addition silicones

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16
Q

What do fillers do?

A
  • more filler=thicker viscosity
  • more filler= lesser contraction (more accurate)
  • more filler= less detail
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17
Q

Accelerator/catalyst for addition silicones:

A

chloroplatini acid catalyst

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18
Q

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

A
  • palladium= it is a hydrogen absorber and hydrogen is what causes the bubbles
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19
Q

Are addition silicones hydrophilic or phobic?

A

hydrophilic!
- different than polysulfudes and condensation silicones

20
Q

which consistency has the least and most filler?

A
  • light (least amount of filler) < regular< heavy < putty (most amount of filler)
21
Q

How is addition silicones dispensed and mixed?

A
  • mixed in cartridge and dispenses in gun
  • more accurate and not wasting much material (only waste in mixing tube)
22
Q

How does the heavy wash/1 stage impression work?

A
  • heavy body in tray
  • wash material or light body around tooth
23
Q

How does putty wash/2 stage impression work?

A
  • first, putty impression before prepping teeth
  • then add heavy body in tray and light body around teeth
  • better detail in all the teeth
24
Q

Addition silicone properties:

A
  • almost odorless
  • naturally hydrophobic (catalyst inside to change it though)
25
Q

Addition silicone setting reaction:

A
  • rapid
    working time: 1-2 minutes
    setting time: 4-5 minutes
26
Q

Chain lengthen increases

A

viscosity

27
Q

Chain cross-linking increases

A

elasticity

28
Q

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

A

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

29
Q

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

A
  • addition silicones
  • polyether
30
Q

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

A

vinyl polyether silicone

31
Q

Properties of vinyl polyether silicone:

A
  • 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)
32
Q

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

A

silicones
- but means they set quicker

33
Q

Which have the most rapid setting function of time?

A
  • addition silicone
    -polyether
    (due to low viscosity)
34
Q

Decreasing viscosity will _______ shear rate

A

increase

35
Q

Words for impression material thinning out when applying force:

A

shear thinning, pseudo plastic, thixotropic

36
Q

Working/setting times in order:

A

polysulfide (longest) > silicones > polyethers (shortest)

37
Q

Working/setting times are shortened by:

A

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

38
Q

Shrinkage of impression material due to:

A
  • evaporation of byproducts
  • thermal contraction
  • rearrangement of bonds during polymerization
39
Q

Dimensional changes/shrinkage in order of material:

A

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

40
Q

Shrinkage occurs towards the ____

A

tray

41
Q

Which materials can affect the dimensional change by absorbing water?

A
  • polyether and hydrophilic addition silicone
  • don’t wrap up in wet paper towel because then it will swell and cast will be smaller
41
Q

Order of permanent deformation/elastic recovery of impression material:

A

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

42
Q

Order of flexibility/strain of impression materials:

A

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

43
Q

Which material have the lowest flow?

A

silicones and polyether

44
Q

Order of hardness of impression materials:

A

polyether (hardest > addition silicone > condensation silicone > polysulfide

45
Q

Order of tear strength of impression materials:

A

polysulfide (highest resistance) > silicones > polyether

Indirect Exam 2 (7 decks)

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