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Dental Biomaterials > Impression Materials > Flashcards

Impression Materials Flashcards

1
Q

What does good dimensional stability mean?

A

Material is likely to retain their size and shape well

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2
Q

If a material does not have good dimensional stability, what is likely to happen to it?

A

The material can shrink, expand, warp, depending on the storage conditions and time

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3
Q

When are rigid impression materials used?

A

Enters the mouth as a viscous liquid and leaves as a solid

Edentulous patients without bony undercuts

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4
Q

What are the properties of plaster of paris?

A

Based on gypsum - calcium sulphate hemihydrate

Low viscosity so mucostatic - does not compress the mucosa

Can be used with a wash material with compo

Good dimensional stability

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5
Q

How is plaster of paris formed?

A

Powder mixed with water which initiates the setting reaction

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6
Q

What are the properties of impression compound?

A
  • Thermoplastic resin or wax based material
  • High viscosity so mucocompressive - compresses the mucosa
  • Poor dimensional stability
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7
Q

How does compound work?

A
  • Material heated above its glass transition temperature above which it melts and is a liquid
  • Sets on cooling
  • Used to make special tray, can use ZnoEu afterwards
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8
Q

What are the general properties of ZnOEu?

A
  • 2 paste system comprising ZnO with various oils and eugenol with various fillers
  • Low viscosity so mucostatic
  • Good dimensional stability
  • Can cause a burning sensation and persistent taste in the mouth
  • Does not need adhesive in tray
  • Special tray is required - fitted to patient first
  • v v good detail
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9
Q

What are the advantages of PoP?

A
  1. No unpleasant flavour
  2. Good dimensional stability
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10
Q

What are the disadvantages of PoP?

A
  1. Must take care to avoid air bubbles which create an inaccurate impression
  2. Special tray required
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11
Q

What are the disadvantages of compo?

A
  1. Poor dimensional stability, model must be poured quickly
  2. Poor detail reproduction owing to high viscosity
  3. Water bath and substantial time required for heating
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12
Q

What are the advantages of ZnOEu?

A
  1. Good dimensional stability
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13
Q

What are the disadvantages of ZnOEu?

A
  1. Some patients find taste/sensation unpleasant
  2. Special tray required
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14
Q

What are the properties of agar?

A
  1. A thermoplastic reversible impression material
  2. Sets when cooled and melts when warmed
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15
Q

What is agar made of?

A
  1. Seaweed
  2. A long chain of polysaccharides derivatives from marine algae
  3. Warmed in a water bath, agar becomes a liquid. Cools and sets to a flexible solid.
  4. Hydrophilic - adapts well to moist surfaces so has good detail reproduction
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16
Q

What are the properties of alginate?

A
  1. Chemically setting impression material
  2. Sets when a chemical reaction occurs - not reversible
  3. Widely used on clinic when only moderate accuracy and stability is required.
  4. Can be used on broken skin - biocompatible
17
Q

When is alginate used?

A

Mouthguards
Dentures
Whitening trays

18
Q

What is alginate made of?

A
  1. Polymer - sodium alginate and calcium salts
  2. Fillers and other materials to give appropriate physical properties and setting times
  3. When powder is mixed with water, the setting reaction starts
19
Q

How does alginate set?

A

Water is mixed with the powder causing the calcium salts to dissolve releasing Calcium ions which replace the sodium ions in the alginate

Divalent calcium forms bridges between adjacent polymer chains

Liquid becomes a flexible solid which can be removed from undercuts

Fillers provide strength

Must be kept moist during transit or else will shrink and become brittle

20
Q

What are the advantages of agar?

A

Good detail reproduction

Cheap

21
Q

What are the disadvantages of agar?

A

Poor dimensional stability
Required a specialist water bath
Special water cooled tray required for clinical use
Main used in lab

22
Q

What are the advantages of alginate?

A

Cheap
Moderately good detail reproduction
Can hasten setting by using warm water

23
Q

What are the disadvantages of alginate?

A

Takes practice to mix properly
Poor dimensional stability and can tear easily on removal
Difficult to disinfect - short term spray causes little distortion but anything more causes impression to swell/distort

24
Q

What are the properties of silicones? (addition cured polyvinyl siloxanes)

A
  • Polymer based on an Si-O-Si-O-Si backbone with vinyl groups
  • 2 paste system supplied in a cartridge that mixes whilst it dispenses
  • Various viscosities and wash versions
  • Expensive
25
Q

What are the general properties of Polyethers?

A
  • Polymer based on a C-C-C backbone with imine groups
  • A two-paste system mixed in a cartridge or by hand
  • Some viscosities available but fewer available than silicones
  • Cheaper but more time consuming
26
Q

What are the properties of condensation cured polyvinyl siloxanes?

A
  • An alternative silicone that released a by-product (a light alcohol) on setting
  • Has poor dimensional stability compared to addition cured silicones hence are less popular
27
Q

What are the properties of polysulfides?

A

Polymer that sets by cross linking and lengthening of the chains via mercaptan -SH groups

Foul smell and taste means that this material has been superseded by other alternatives

Smell like rotten eggs

Dental Biomaterials (5 decks)

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