Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

YR3 DMS > Impression Materials - Types > Flashcards

Impression Materials - Types Flashcards

1
Q

What are the 2 main classifications of impression materials?

A

Elastic

Non Elastic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the two states that hydrocolloids exist in and explain these

A

Sol = fluid with low viscosity, random arrangement of polysaccharide chains

Gel = high viscosity, organised arrangement of polysaccharide chains

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

The strength of a hydrocolloid depends on two things. What are they?

A
  1. Concentration of fillers

2. Concentration of fibrils

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is syneresis and imbibition and why does this happen with hydrocolloids?

A

Syneresis = gel molecules come closer and water is squeezed out

Imbibition = water is taken up in presence of moisture due to hydrophilic property

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What makes agar reversible and alginate irreversibel?

A

Agar is formed with physical bonds only meaning that energy provided can break down the matrix and go back to sol state.

Alingate forms with chemical bonds which cannot be broken with heat.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Why do we want to place impression materials in the mouth in the sol state?

A

Allow flowability into the surface detail

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is found in the powder of aliginate?

A
  • Powder of sodium alginate and gypsum (calcium sulphate)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How does alginate change from a sol to a gel state?

A

Sol state = sodium alginate

Gel state = calcium alginate (calcium cross links with alginate chains)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Why is sodium phosphate added to impression materials?

A

To control working time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why do we not like bubbles in alginate?

A
  • Weak point where impression can tear
  • Rise to the impression surface and cause inaccuracy
  • Lead to more water absorption
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How do calcium ions become available to cross link with in alginate?

A
  • Calcium salts start dissolving when water is added
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Explain how trisodium phosphate reduces the reaction rate?

A

Tri sodium phosphate have 3 sodium ions per phosphate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the main properties of alginate?

A
  • Hydrophilic gives them good flow
  • Easy to mix
  • Fairly cheap
  • Can control setting time
  • Good shelf life
  • Mucostatic
  • Good working and setting time
  • Poor dimensional stability
  • Poor tear resistance
  • Messy so can cause patient to gag
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How do addition cured silicones set?

A
  • Cross linking of hydrogen across double bond to cause setting
  • Presence of platinum catalyst
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the main properties of addition cured silicones?

A
  • Good dimensional stability
  • Good accuracy
  • Available in different viscosities
  • HYDROGEN EVOLUTION : platinum catalyst reacts with hydrogen leads to surface pitting and creates a rough surface
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How does condensation silicones set and what is the catalyst used?

A

Two molecules react together (hydroxy terminated poly(dimethyl siloxane) in presence of alkyl silicate (cross-linking agent)

Tin catalyst

17
Q

What molecule is released in condensation silicones?

A

2 ethyl alcohol molecules

18
Q

What are the main properties of condensation cured silicones?

A
  • Short working time
  • Near ideal elastic recovery
  • Hydrophobic (can cause blow holes with saliva present)
  • Good tear strength
  • High amount of shrinkage
  • Accurate
  • Easy to use
19
Q

What are polyethers supplied as?

A

Two pastes

  1. Polyether with filler and plasticiser
  2. Catalyst paste (enhance polymerisation)
20
Q

What type of setting reaction do polyethers undergo and how long does it take?

A

Addition polymerisation

6-7 mins

21
Q

Are there any bi products in the poly ether setting reaction?

A

No - no shrinkage

22
Q

What are the main properties of polyethers?

A

Hydrophilic so flows over surface tissues.

Good shelf life

Good elastic recovery

Low tear strength

Rapid setting time, short working time

Stiff so hard to remove it out mouth

Only can be used as 1 viscosity

23
Q

During the setting of alginate impression materials, what happens?

A) Trisodium phosphate reacts with sodium alginate
B) Trisodium phosphate reacts with calcium sulphate
C) Colloidal changes to sol
D) Material in contact tight soft tissues sets last

A

B

YR3 DMS (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions