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Sp 15- Fixed Restorative Final > Johnston: Impression Materials > Flashcards

Johnston: Impression Materials Flashcards

1
Q

When referring to the balance of dimensional changes associated with impressions and casts, which has a (-) change and which has a (+) change?

A

Impression (-)
ex. Alginate will start to shrink over time
Cast or Die (+)
ex. Gypsum products will expand

Together: Alginate + Gypsum = ZERO (ideal)

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2
Q

When referring to the balance of dimensional changes associated with “investment” and “restoration” which will have a (-) change and which will have a (+) change?

A

Investment: + + +
Restoration - - -

Must add up to ZERO

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3
Q

What are the three physical classifications of impression materials?

A

Rigid
Plastic
(Visco)Elastic

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4
Q

What are two examples of rigid impression materials used in dentistry?

A

ZOE

Plaster

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5
Q

What are two examples of plastic impression materials used in dentistry?

A

Wax

Compound

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6
Q

What are the two broad categories of (visco)elastic impression materials used in dentistry?

A

Hydrocolloids

Synthetic Elastomers

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7
Q

Which type of physical-classification of impression materials is used for edentulous patients only?

A

Rigid or Brittle Materials
ex. Zinc Oxide & Eugenol Impression Paste
Dental Impression Plaster

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8
Q

What are two examples of Hydrocolloid impression materials? How do the two differ?

A

Hydrocolloids (type of visoelastic material)

  1. Reversible Hydrocolloid (Agar)
  2. Irreversible Hydrocolloid (Alginate)
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9
Q

What are synthetic elastomers?

A

Synthetic elastomers are a type of visoelastic impression material that are made by polymerizing oligomers into elastomers

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10
Q

What are the three categories of synthetic elastomers in dentistry? Is there a possible fourth category?

A
  1. Polysulfide
  2. Silicone
  3. Polyether
    (4. New Product: combination of Silicone and polyether)
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11
Q

What are the two types of Silicone viscoelastic impression materials?

A
  1. Addition

2. Condensation

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12
Q

What is the difference between “light body” and “heavy body” impression materials?

A

Light Body is applied via syringe or wash
Heavy Body is applied via tray or putty
Light Body has low viscosity and high contraction
Heavy Body has high viscosity and low contraction

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13
Q

True or False: Light and Heavy body are used together with light body surrounding/capturing the area of interest.

A

True

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14
Q

Hydrocolloid impression materials are characterized by water bound within a _____ _______.

A

Colloid Matrix

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15
Q

Hydrocolloid impression materials (both reversible and irreversible) lack _____ ______ with time and require ______ pouring of casts.

A

Dimensional Stability

Immediate

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16
Q

What are the benefits to using irreversible hydrocolloid material (such as alginate)?

A

Convenient

Relatively inexpensive

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17
Q

What is the benefit and downfall associated with reversible hydrocolloid material (such as agar)?

A

Benefit: Good initial dimensional accuracy
Downfall: Requires special heating/cooling equipment

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18
Q

True or False: Reversible and Irreversible Hydrocolloid impression materials may not be used in combination.

A

False: they MAY be used in combination

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19
Q

When categorizing polymers, they can be either thermoplastic or thermoset. What is the difference?

A

Thermoplastic: NO CROSS-LINKING, physical state is
reversibly controlled by temperature
Thermoset: CROSS-LINKING is IRREVERSIBLE and occurs
during the transformation from monomer
to polymer

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20
Q

What is an example of a thermoplastic polymer? Thermoset polymer?

A 
Thermoplastic = wax
Thermoset = synthetic elastomer
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21
Q

What are the addition polymerization mechanisms? Give three examples. Which is used in Dentistry?

A

Addition polymerization is the change from monomer to polymer WITHOUT by-products.

  1. Free Radical Dental
  2. Ring opening
  3. Ionic
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22
Q

What type of polymerization reaction do polysulfide materials use?

A

Condensation

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23
Q

Polysulfide materials have ____ molecular weight oligomers containing reactive ______ groups.

A

Low

Mercaptan

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24
Q

True or False: Polysulfide impression materials conform well to a prepared tooth and result in good surface detail.

A

True

25
Q

During the polymerization reaction of polysulfide materials, lead dioxide or copper hydroxide will oxidize and form a polysulfide _____ with a _____ condensate.

A

Rubber
Water

*remember: polysulfides polymerize through condensation reactions

26
Q

Polysulfides and Polyethers both require _________.

A

Rigid Custom Trays for minimal thickness of impression material

27
Q

Why do polysulfides and polyethers require custom trays?

A

To provide minimum thickness of impression material

28
Q

What is the major flaw associated with polysulfide impression material?

A

They do NOT recover from permanent deformation very well (deformation is associated with removal of the material from the mouth)

29
Q

True or False: When using Polysulfide material, the casts should be poured as quickly as possible.

A

True.
They do not recover well from permanent deformation
Water condensate produced during reaction = evaporation = shrinkage

30
Q

Silicone empression materials (polysiloxanes) are inherently __1__ but addition type can be made more __2__.

A
  1. Hydrophobic

2. Hydrophilic

31
Q

Which type of silicone was first introduced?

A

Condensation type (hydrophobic)

32
Q

How can silicone impression materials be made more hydrophilic?

A

(Original Condensation type are hydrophobic.)
Addition type is made hydrophilic via:
1. Addition of surfactant
2. Chemical incorporation of hydrophilic moieties into
the silicone backbone

33
Q

Which impression material is classified as: a low molecular weight oligomer containing terminal hydroxyl groups that will eventually form a rubber and release ethyl alcohol?

A

Condensation Silicone

34
Q

True or False: When using condensation silicone impression material, the casts should be poured as quickly as possible.

A

True

35
Q

Which type of impression material will release alcohol as a result of the polymerization reaction?

A

Silicone

36
Q

Addition silicone materials are low molecular weight polymers with terminal silane and vinyl groups that are now supplied with a _______ to make the material more hydrophilic.

A

Surfactant

37
Q

Addition silicone materials go through _____polymerization in the presence of chloroplatinic acid (platinum) in order to cross-link/chain-lengthen.

A

Ionic

typically we talk about free-radical polymerization

38
Q

High contact angles are associated with ________ materials and incorporation of _______.

A

Hydrophobic

Air bubbles

39
Q

Do condensation or addition silicone materials have a higher likelihood for bubbles due to high contact angles?

A

Condensation - Hydrophobic- high CA - bubbles

40
Q

Platinum or Palladium is used in association with Addition silicone materials in order to absorb some of the _______ produced through a secondary reaction of -OH groups.

A

Hydrogen Gas

41
Q

True or False: When using addition silicone impression material, the casts should be poured as quickly as possible.

A

FALSE!
Addition silicones will liberate Hydrogen gas…
pouring should be delayed long enough to liberate it
(THINK: addition silicones: you should wait an ADDITIONal minute)

42
Q

True or False: For extensive impressions, working time of addition silicones may be lengthened but it may adversely affect other properties.

A

False: the retarder may be added, yes! but, it will NOT adversely affect other properties

43
Q

Contamination of addition silicone impression material with sulfur or dithiocarbamate (rubber gloves) before setting will either _____ or ______.

A

Lengthen the set time

Cause the material to not set at all

44
Q

What is a common contaminate of addition silicone that is prevalent in dental offices or labs?

A

Dithiocarbamate contamination from latex rubber gloves

45
Q

What type of polymerization reaction is associated with polyether impression materials?

A

Ring opening

46
Q

Addition silicone materials go through _____ polymerization, whereas polyethers go through _____polymerization.

A

Ionic

Ring opening

47
Q

Which viscoelastic impression material is associated with possible contact dermatitis?

A

Polyether

-contact with unmixed ester

48
Q

When using polyether impression materials, a thinner diluent may be available to adjust and control _____.

A

Viscosity

49
Q

The requirements for ideal impression materials are:

  1. Low _____
  2. Long _______
  3. Bio_________
  4. ________ to patient
A
  1. Cost
  2. Shelf-life
  3. compatability
  4. Pleasant
50
Q

Before setting, ideal impression materials should have 1. ______ of manipulation, 2. Control over ____ _____, and 3. ____ ____ on moist oral structures.

A
  1. ease
  2. setting time
  3. Good wetting (low contact angle)
51
Q

During setting, what are two requirements for ideal impression materials?

A
  1. No dimensional change

2. Short setting time

52
Q

After setting, ideal impression materials should have:

  1. _____ flexibility
  2. ______ tear strength (rate of strain)
  3. ______ elastic recovery
  4. _____ dimensional change from applied stress
A
  1. High
  2. High
  3. High
  4. No
53
Q

High tear strength is a function of _____ of strain.

A

Rate

54
Q

After setting, ideal impression material should have no dimensional change from ______ _____ or _____ _____.

A

Applied stress

Upon Standing

55
Q

Ideal impression materials should be compatible with ____ and with ____ materials.

A

disinfectants

cast or die materials

56
Q

Why is it important for impression materials to be compatible with die or cast materials?

A
  • In order to reproduce fine details
  • To limit the contact angle
  • To limit chemical retardation of the cast
57
Q

When looking at a graph that compares impression materials to “reproduction limit,” how does Alginate compare to other materials?

A

Alginate has a HIGH reproduction limit…meaning it does not capture fine details as well as the other materials

58
Q

When considering dimensional accuracy of impression materials, in which direction does shrinkage typically occur?

A

Shrinkage occurs TOWARD the tray from above the plane (HEIGHT)

59
Q

Which impression material has the highest dimensional change upon standing and lowest elastic recovery?

A

Polysulfide

Sp 15- Fixed Restorative Final (10 decks)

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