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BDS 2: Dental Materials > Impression Materials > Flashcards

Impression Materials Flashcards

1
Q

All Elastic impression materials, which include alginates, agar and all elastomers are what in their unset state?

A

Polymers

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2
Q

All impression materials except agar do what on setting?

What does agar do instead?

A
  • Chemically cross-link on setting

- Agar sets by a physical, reversible process

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3
Q

What are elastomers used for? (2)

A
  • To produce an accurate replica of the teeth and supporting tissues
  • For the construction of full and partial dentures, crowns, bridges and inlays
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4
Q

Compare the cost of elastomers to alginates and agar

A

Elastomers cost significantly more than alginates/agar

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5
Q

How are elastomers dispensed?

describe unset/set states

A

2 paste systems that are fluid in the unset state, which are cross-linked (elastic) in the set state

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6
Q

When does chemical cross linking occur in a two paste system?

A

As soon as the two components come into contact with each other, the chemical cross-linking reaction (setting) begins

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7
Q

When does chemical cross linking occur in a one paste system?

A

As soon as the LED light unit is directed on to the paste

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8
Q

How can two paste systems be supplied? (3)

A
  • Two separate tubes
  • Two tubs of putty
  • Putty and tube
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9
Q

What are the advantages of supplying two paste systems in double barrel cartridges or pouches? (2)

A
  • Avoid incomplete mixing

- Prevent introduction of air bubbles

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10
Q

In elastomers how are the polymer cross-links carried out?

A

Either condensation or addition reaction

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11
Q

How does the differing cross-link reaction in elastomers affect the dimensional stability of the set material?

A
  • Addition reaction results in no by-products therefore material does not shrink on setting
  • Condensation reaction results in the elimination of a small molecule thus resulting in shrinkage of the set material
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12
Q

What type of bonds are cross links?

A

Cross-links are covalent bonds joining one polymer chain to another

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13
Q

What are the different viscosities of elastomeric impression materials? (5)

A
  • Putty
  • Heavy
  • Medium
  • Light
  • Wash
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14
Q

Describe the difference in amounts of filler used in Putty and Wash elastomeric impression materials?

A
  • Putty has maximum amount of filler

- Wash has least amount of filler

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15
Q

When pairing different viscous pastes, what elastomeric impression material pastes would you usually combine together?

A
  • Putty with wash material

- Heavy/Medium with light-bodied material

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16
Q

Why can’t the light-bodied/wash materials be used by itself?

A

Due to it containing little filler, it does not have the strength (and body), and so it will tear easily when removing the impression from the mouth

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17
Q

Explain the role of each material when combining a light-bodied and heavy-bodied material

A
  • The light-bodied material records the fine detail

- The heavy-bodied material acts as a base to support the light material

18
Q

Explain the ‘one stage’ putty and wash technique

A
  1. The wash material is syringed around the teeth or prepared tooth
  2. The putty is loaded into the tray and inserted immediately in the mouth after syringing the wash material in the mouth
19
Q

Explain the ‘two stage no spacer’ putty and wash technique

A
  1. The putty is used first to take an impression of the
    mouth before starting the preparation
  2. After preparing the teeth the wash material is syringed on the prepared teeth and, the tray with putty impression is reinserted over the wash
20
Q

Explain the ‘two stage with spacer’ putty and wash technique

A
  1. A polythene sheet is placed over the teeth
  2. The putty is then used to take an impression of the mouth by placing over the polythene sheet
  3. After set, the putty impression is removed from the mouth and so is the polythene sheet removed
  4. The wash material is placed in the space provided in the putty impression and the tray is seated back in the mouth
21
Q

Explain the dual viscosity technique

A
  1. Heavy and light-bodied pastes are used in combination
  2. Heavy or medium-bodied material is extruded into the tray
  3. Light-bodied material is syringed around the teeth (area of interest) and can also be placed on the heavy/medium material in the tray
22
Q

Which materials take longer to set, light or heavy bodied?

A

Light bodied material will take longer to set

23
Q

What is the main advantage of using impression techniques?

A

Fine detail recorded

24
Q

Give a disadvantage of the ‘one stage’ putty and wash technique

A

Both materials have to be mixed simultaneously

25
Q

Give a disadvantage of the ‘two stage’ putty and wash technique

A

You have to take 2 impressions which can be long

26
Q

What are condensation silicones commonly known as?

A

Polydimethyl siloxanes (PDMS)

27
Q

Is PDMS/PVDMS hydrophobic or hydrophilic?

What does this mean when taking an impression?

A
  • Hydrophobic

- Mouth has to be dry otherwise defects in impression material

28
Q

What are the two pastes called in condensation silicones?

A
  • Base paste

- Catalyst paste

29
Q

What is the base paste of a condensation silicone made up of? (2)

A
  • Silicone polymer with terminal OH-groups

- Inert filler

30
Q

What is the catalyst paste of a condensation silicone made up of? (3)

(list the functions of each)

A
  • Tetraethoxy orthosilicate (cross-linking agent)
  • Dibutyl tin dilaurate (catalyst)
  • Inert filler
31
Q

In a condensation silicone reaction what product is lost in the reaction?

Where are parts of of this product from?

A
  • C2H5OH (ethanol)
  • C2H5 from Tetraethoxy Orthosilicate
  • OH from base polymer
32
Q

What are some advantages of condensations silicone? (4)

A
  • Stronger and have better dimensional stability than alginates
  • They are more elastic than polysulphides and polyethers, therefore they recover from deformation rapidly
  • Tear strength is adequate
  • Elongation at break is adequate
33
Q

What are some disadvantages of condensations silicone? (5)

A
  • Shrink in air
  • Hydrophobic
  • Expand in disinfectant
  • Erratic setting behaviour when a liquid catalyst is used in place of a catalyst paste
  • Limited shelf life, mainly with liquid catalyst
34
Q

What are addition silicones commonly known as?

A

Polyvinyldimethyl siloxanes

PVDMS

35
Q

What is the base paste of an addition silicone made up of? (2)

A
  • Base paste

- Catalyst paste

36
Q

What is the base paste of an addition silicone made up of? (2)

A
  • Silicone polymer with terminal vinyl groups

- Inert Filler

37
Q

What is the catalyst paste of an addition silicone made up of? (3)

A
  • Silicone oligomer with Si-H groups (cross-linking agent)
  • Platinum salt catalyst
  • Inert filler
38
Q

Draw/Give a vinyl group

A

CH2=CH

39
Q

What are some advantages of addition silicone? (2)

A
  • Best dimensional stability compared to all other impression materials
  • Elastic recovery is very good
40
Q

What are some disadvantages of addition silicone? (3)

A
  • When pouring, free water in plaster/stone reacts with the unreacted Si-H groups in the set material, thus releasing hydrogen and giving a porous model (so wait 30 mins before pouring)
  • Setting can be seriously impaired when handled with natural rubber gloves
  • Hydrophobic material

BDS 2: Dental Materials (13 decks)

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