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Pulse - Dental Materials > Elastomeric impression materials > Flashcards

Elastomeric impression materials Flashcards

1
Q

What are polysulphides also known as?

A
  1. First dental elastomers
  2. Vulcanizing impression materials
  3. Mercaptan impression materials
  4. Thiokol
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2
Q

What colour is polysulphide?

A

Brown

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3
Q

What gives polysulphide its colour?

A

Lead dioxide polymer

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4
Q

What is the nature of the polymerization reaction of polysulphides?

A

Exothermic

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5
Q

What is the setting time of polysulphides?

A

8 - 12 minutes

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6
Q

Are polysulphides comfortable for the patient?

A

No. Unpleasant odour and colour. It’s messy and stains clothes.

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7
Q

How can you accelerate polysulphide setting time?

A

Heat and moisture.

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8
Q

Are polysulphides dimensionally stable?

A

No. Max permanent deformation.

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9
Q

How soon must cast be poured after polysulphide impression is made?

A

Within 30 minutes to preclude chances of deformation.

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10
Q

What causes dimensional change in polysulphides?

A

High amount of polymerisation shrinkage

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11
Q

What causes polymerisation shrinkage in polysulphides?

A

Loss of water, which is the byproduct of the polymerisation reaction.

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12
Q

How can polymerisation shrinkage and permanent deformation be avoided with polysulphides?

A
  1. Taking minimum quantity of impression material

2. Using a custom acrylic tray

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13
Q

One redeeming quality of polysulphide impression materials

A

Shows highest tear strength

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14
Q

What is the relation of polysulphide impression materials with water?

A

Hydrophobic. Impression area needs to be dried before making an impression with polysulphide.

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15
Q

What, along with high tear strength, makes polysulphides suitable for recording deep undercuts?

A

High flexibility - the material can be released from the undercut areas with minimum stress.

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16
Q

Biocompatibility of polysulphides.

A

Good – causes lowest cell death count.

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17
Q

What sets polysulphides apart from all the other impression materials?

A

They’re the only material that can be electroplated.

18
Q

What are Room Temperature (RTV) silicones?

A

Condensation silicone

19
Q

Which elastomeric impression material has the highest curing shrinkage?

A

Condensation silicone, because of evaporation of ethyl alcohol byproduct.

20
Q

How soon must cast be poured after a c-silicone impression is made? Why?

A

30 minutes - to avoid curing shrinkage.

21
Q

How is the deformation of condensation silicone compared to polysulphides?

A

C-silicones show less permanent deformation compared to polysulphides.

22
Q

Relationship of c-silicones to water.

A

Hydrophobic.

23
Q

Flexibility of c-silicones.

A

HIgher than polysulphides - can be removed from undercuts without distortion.

24
Q

Shelf life of c-silicones

A

Limited, because of oxidation of the tin component.

25
Q

Handling of c-silicones

A

Latex gloves contraindicated.

26
Q

PVS Impression material

A

Addition silicones

27
Q

Addition silicones, aka

A
  1. Pseudoplastic impression materials
  2. Polyvinyl siloxane
  3. Vinyl Poly siloxane
28
Q

What is a big advantage a-silicones have over c-silicones and polysulphides?

A

No volatile byproduct.

29
Q

How soon must cast be poured after an a-silicone impression is made?

A

Casts can be poured after several hours -

  1. Lowest curing shrinkage
  2. Lowest permanent deformation
  3. Best dimensional stability
30
Q

Relation of PVS to water

A

Extremely hydrophobic

31
Q

Setting time of pseudoplastic impression material

A

Least setting time of all elastomeric materials.

32
Q

Handling of a-silicone

A

Latex gloves contraindicated - sulphur present in latex gloves inhibits setting of a-silicones.

33
Q

Shelf life of PVS

A

Better than condensation silicones

34
Q

Disinfection of a-silicones

A

Immersion in

  1. 10% hypochlorite
  2. 2% glutaraldehyde
35
Q

Issues with a-silicones

A

Sometimes hydrogen may be evolved and may cause pinpoint voids in stone casts.

36
Q

Which was the first elastomer to be developed specifically as an impression material?

A

Polyether

37
Q

Stiffness of polyether

A

Stiffest of all elastomers - extremely difficult to remove from undercut areas because of high modulus of elasticity.

38
Q

Tear strength of polyether

A

High - second only to polysulphides.

39
Q

Dimensional stability of polyether

A

High - cast can be poured after several days and several times without altering dimensional stability.

40
Q

Biocompatibility of polyether

A

Not good - highest cell toxicity.

41
Q

Relationship of polyether with water

A

Only hydrophilic elastomeric impression material.

Pulse - Dental Materials (3 decks)

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