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D2 - FALL - Par 3 > Fixed - Impression Materials > Flashcards

Fixed - Impression Materials Flashcards

1
Q

What is accuracy?

A

Accuracy: Ability to replicate the intraoral surface details.

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2
Q

What is dimensional stability?

A

Dimensional Stability: Ability to retain its absolute dimensional size over time.

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3
Q

What is tear resistance?

A

Tear Resistance: Ability to resist tearing in thin sections (such as through feather-edged material within the gingival sulcus.)

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4
Q

What are the non-water based rigid impression materials and which one is the only physical reversible material?

A
  1. impression plaster
  2. impression compound
  3. zinc oxide eugenol

*impression compound = only physical set, reversible rxn rigid material

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5
Q

What is the most common impression material and what is its shortcomings?

A

Alginate (irreversible hydrocolloid that sets up due to irreversible chemical rxn.)
- shortcoming = *not accurate enough for fixed and removable restorations.

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6
Q

What are the 2 types of water-based rigid impression materials? And what type of reactions and sets are they?

A
  1. alginate - irreversible, chemical

2. agar-agar - reversible, physical

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7
Q

What does sodium phosphate do in alginate?

A

React preferentially with calcium ions to provide working time before gelation

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8
Q

What does diatomaceous earth or silicate powder do in alginate?

A

Control the consistency of the mixed alginate and the flexibility of the set impression

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9
Q

What does organic glycols do in alginate?

A

Makes the powder dustless

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10
Q

Changes in water/powder ratio will alter what?

A

consistency & setting times of the mixed material

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11
Q

What do you add to reduce setting time or slow the reaction down?

A

trisodium phosphate

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12
Q

What are the 2 main rxns of the alginate process?

A

1st: 2Na3PO4 + 3CaSO4 Ca(PO4)2 + 3Na2SO4

2nd: K2Alginate (powder) + CaSO4
Powder
Water
K2SO4 +
CaAlginate (gel)
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13
Q

what are the general properties of alginates?

A
  • Highly hydrophilic.
  • Expand slightly during setting rxn.
  • Sensitive to ambient humidity
  • Low tear strength.
  • Short shelf life (<1year).
  • Accuracy & reprod. of detail is limited.
  • Dimensionally unstable–remember water can come in and out depending on the storage environment.
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14
Q

What are the 4 types of elastomeric impression material?

A
  1. polysulfide (rubber base, thiokol)
  2. silicone (conventional, condensation)
  3. polyether
  4. polyvinyl siloxane (addition silicone, vinyl polysiloxane)

*all flexible properties, irreversible rxn, chemical set

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15
Q

ISO 4823 requirements?

A
  1. consistency
  2. detail reprod.
  3. linear dimensional change
  4. compatibility w/ gypsum
  5. strain in compression
  6. elastic recovery
  7. report working time & setting time
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16
Q

What are the 4 types of ISO consistencies?

A

Type 0: putty consistency
Type 1: heavy-bodied consistency
Type 2: medium body consistency
Type 3: light-bodied consistency

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17
Q

What does the continuous phase involved?

A

Flexible matrix
• Multifunctional pre-polymer or polymer.
• Crosslinking agent.
• Curing agent (catalyst or initiator).
• Modifiers (accelerators, retarders, plasticizers, flavoring agents, colorants).

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18
Q

What does the dispersed phase involve?

A

filler or extender

19
Q

Would a filled polymer have high or low shrinkage?

A

low shrinkage.

  • unfilled polymer has high shrinkage
20
Q

What are 2-step techniques you can use to manage shrinkage?

A
  1. light-heavy body

2. wash-putty

21
Q

During setting shrinkage, distortion of impression is toward the ____.

A

tray

22
Q

Dies tend to be slightly ____, so the casting is also slightly ____.

A

oversized, oversized

23
Q

How would you do the light-heavy body technique?

A

cover prep w/ light-bodied IM from syringe; load tray w/ heavy bodied-IM

*this is what we do in lab

24
Q

The ____ the removal of the tray the less distorion. (slower/faster)

A

faster; use very fast snap!

25
Q

What are the mixing options for elastomeric impression materials?

A

Mixing Options:
• 2 Pastes on a mixing pad.
• 2 Pastes in mixing gun (Kenics mixing tip).
• 2 Pastes in mixing machine (Kenics mixing tip).

26
Q

A _____ material is one in which viscosity increases with the rate of shear strain.

A

dilatant (also termed shear thickening)

  • mix pad
27
Q

_____ is an effect where a fluid’s viscosity—the measure of a fluid’s resistance to flow—decreases with an increasing rate of shear stress.

A

Shear thinning (pseudoplastic)

  • auto-mix gun or machine
28
Q

what are the general properties of polysulfide IM?

A

aka rubber base, mercaptan rubber; works best in custom tray; not very good w/ pts (smelly, bad taste, stains clothes)

29
Q

Examples of shear thinning IM’s?

A

polyether, polyvinylsiloxane

30
Q

Examples of shear thickening IM’s?

A

silicone rubber, polysulfide rubber

31
Q

what are the general properties of silicone rubber IM?

A
  • Limited shelf-life: Unstable in tubes.
  • Requires mechanical retention or special tray adhesives.
  • No syneresis or imbibition, but continued polymerization shrinkage.
  • Better dimensional stability than reversible hydrocolloid but more expensive.
  • Pouring of models:
  • More flexible so more chance for distortion during removal.
  • Wait 20-30 minutes before pour for stress relaxation to occur.
32
Q

For polyether rubber, what is involved in the continuous phase & dispersed phase?

A

CONTINUOUS PHASE:
• Polymer: Amine-terminated polyether.
• Crosslinking agent in the catalyst: Aromatic sulfonate.
• Modifiers: Colorants, glycol plasticizers, flavorants.

DISPERSED PHASE:
• Fillers: Silica.

33
Q

Why is silica put in as a filler during the dispersed phase?

A

to improve stability of the iM

34
Q

What is the setting rxn for polyether rubber?

A

SETTING REACTION: Stepwise (relatively slow); exothermic; affected by temperature

35
Q

what are the general properties of silicone rubber IM?

A
  • Excellent impression accuracy and dimensional stability.
  • Stiff and therefore difficult to remove without rocking.
  • Break seal and rock slightly to prevent tearing: Low tear resistance.
  • Negatively affected by H2O, saliva, and blood.
  • Since hydrophobic, moisture increases marginal discrepancy.
  • Increased water absorption occurs if use thinning agents.
  • Can be dispensed from automated extruder and mixer (ESPE PentaMix).
36
Q

For polyvinyl siloxane, what is involved in the continuous phase & dispersed phase?

A

CONTINUOUS PHASE:
• Polymer: Double-bond-functional silicone polymer.
• Crosslinking agent and catalyst: Chloroplatinic acid.
• Modifiers: Colorants, flavorants, plasticizers.
DISPERSED PHASE: Fillers: Silica.

37
Q

What is the setting rxn for polyvinyl siloxane?

A

SETTING REACTION:

Chain (very fast), exothermic; affected by temperature; hydrogen gas released by decomposition of crosslinking agent.

38
Q

What is good about polyvinyl siloxane’s setting process?

A

The reaction is essentially complete at the time of removal = allows for no distortion (or
very limited)

39
Q

what are the general properties of polyvinyl siloxane IM?

A
  • BEST impression material for dimensional stability:
  • Pouring should be delayed for H2 out-gassing.
  • Pouring can be delayed up to7-to-10days (or indefinitely).
  • Stiffness makes removal difficult.
  • Most material dispensed using auto-mixing gun and mixingtips.
40
Q

Accuracy of IM in order of good to poor for wetting tissues?

A

Wetting of tissues: RHC, PVS => PE > PS, Sil > ALG

41
Q

Accuracy of IM in order of good to poor for wetting stone?

A

RHC, ALG => PE > PS > Sil, PVS

42
Q

Dimensional stability of IM in order of good to poor? (involves polymerization shrinkage, loss of components, thermal shrinkage, stress relaxation)

A

PE, PVS >PS, Sil >RHC >ALG

43
Q

Tear resistance of IM in order of good to poor for elastic deformation & strain rate sensitivity?

A

PS>Sil,PVS >PE,RHC,ALG

44
Q

Remember: PVS’s qualities as far as accuracy, dimensional stability, tear resistance.

A 
PVS = 2nd from top in accuracy
PVS = 2nd from top in dimensional stability
PVS = was 2nd/3rd spot from top of list in tear resistance.

*PVS = intermediate in all 3 categories; best trait = tear resistance

D2 - FALL - Par 3 (10 decks)

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