Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

BDS 2: Dental Materials > Alginates > Flashcards

Alginates Flashcards

1
Q

What are impression materials used for?

A

Used to produce a detailed replica of the teeth and oral tissues

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

What are the 3 types of elastic impression materials?

A
  • Hydrocolloids
  • Elastomers
  • Non-elastic materials
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Give an example of a reversible and irreversible hydrocolloid

A
  • Reversible = Agar

- Irreversible = Alginate

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

What are the 3 types of elastomers?

A
  • Silicones
  • Polysulphides
  • Polyethers
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Name 3 non-elastic impression materials

A
  • ZOE
  • Impression plaster
  • Impression compound
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What makes alginates irreversible hydrocolloids?

A

The reactions sets by a chemical cross-linking reaction

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

What are alginates extracted from?

A

Extracted from seaweed with a hydroxide

Ie with NaOH forms sodium alginate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What happens when alginate is mixed with water?

A

When alginate is mixed with water, it forms a colloidal suspension in it, and then it sets by a chemical cross-linking reaction

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

What is a typical alginate powder composition? (6)

Include percentage composition

A
  • Na/K alginate (12%)
  • Diatomaceous earth (70%)
  • CaSO4 (12%)
  • Na3PO4 (2%)
  • Sodium silicofluoride or Sodium fluorotitinate (4%)
  • Magnesium oxide (3%)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the role of Diatomaceous earth in alginate powder?

A

Acts as a filler to strengthen alginate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the role of CaSO4 in alginate powder?

A

Cross-linking agent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the role of Na3PO4 in alginate powder?

A

Retarding agent

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

What is the role of Sodium silicofluoride, Sodium fluorotitinate and Magnesium oxide in alginate powder?

A

pH controller

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

In sodium alginate polymer where does cross linking occur?

A

At COONa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Define cross link

A

Chemical bonds joining two polymer chains together

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What joins 2 polymer chains of alginates?

What is displaced?

A
  • Ca

- Na in COONa is displaced

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the function of the retarder in alginate powder?

A

Without retarder alginate gels immediately, so a retarder gives working time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How much cross-linking occurs when phosphate ions are present in the powder?

A

The cross-linking reaction is suppressed while the phosphate ions are being used up

So no cross-linking

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Why are pH controllers added to alginate powders?

A
  • When setting pH of alginate initially decreases to below pH 3.5 and rises to pH 9 on setting
  • When set gel is too acidic or alkaline it will give a poor plaster/stone surface
  • So pH controllers are added to decrease the pH to near neutral (~8)
  • In order to make it compatible with casting materials
20
Q

What feature does Chromoclone have that makes the alginate easier to use?

A

Powder colour changes at different pH’s

21
Q

With Chromoclone what colour appears when water is added to alginate?

22
Q

What colour change of chromoclone needs to occur in order to indicate the alginate is ready to be loaded in a tray?

A

Purple to Pink

23
Q

Which colour change indicates that chromoclone in a tray can be inserted into the mouth?

A

Pink to light peach

24
Q

What are some advantages of alginates? (2)

A
  • Very good setting behaviour

- Cheap and reliable

25
What are some disadvantages of alginates? (5)
- Once alginates are set they lose water in air - Immersing the alginate in disinfectant causes initial swelling then shrinking causes poor dimensional stability - Poor tear strength - Does not adhere well to tray - Highly viscoelastic
26
Alginates losing water air once set means what for general properties? (2) How do you manage this?
- Continual shrinkage in air - Poor dimensional stability - Impressions must be covered with a damp napkin and placed in a sealed plastic bag
27
Explain step by step the disinfection protocol for alginates (5)
1. Remove set alginate/tray from the mouth 2. Rinse in tap water to remove blood/saliva 3. Immerse in disinfecting solution for only 10 minutes 4. Remove from disinfecting solution and rinse in tap water 5. Wrap in a damp napkin and seal in a polythene bag (100% relative humidity)
28
What is a disinfectant solution used in alginates?
Sodium hypochlorite
29
Why do you need to shake the alginate tub before using?
- Density of the various ingredients of an alginate powder differ - So there is a tendency for settling out in the tin/tub
30
Why are dust free alginate powders used today? What particle in particular is the cause of this?
Silica particles in the dust are a possible health hazard
31
How do you produce dust free alginate?
Ball-mill (mix/grind) alginate powder with a small amount of ethylene glycol
32
What are the different types of alginate bases? (4)
- Sodium alginate - Potassium alginate - Sodium and Potassium alginate - Triethanolamine alginate
33
What were polyvinyl alcohol sachets?
- Pre-weighed alginate powders in sachets - Sachet made from polyvinyl alcohol, a water soluble plastic - Sachets would dissolve in water - No longer used as expensive
34
By what process is agar set?
Set by a Physical Process
35
What state is agar in at room temperature? What state is agar in at 60°? What occurs to agar when cooled form 60°?
- A solid (gel) at room temperature - A viscous liquid at 60°C - On cooling, it reverts to the gel
36
What is the composition of agar impression material? (4)
- Agar (13-17%) - Borates (0.2-0.5%) - Potassium sulphates (1-2%) - Thixotropic materials (0.5-1%)
37
What is the function of agar in agar impression materials?
Colloid
38
What is the function of borates in agar impression materials?
Strengthens gel
39
What is the function of potassium sulphates in agar impression materials?
Accelerates setting of stone
40
What is the function of Thixotropic materials in agar impression materials?
Filler
41
Why are agar dispensed in tubes?
Prevent water loss
42
What is agar squeezed into?
Special metal tray
43
What occurs before placing agar into its metal tray?
- Tubes are put into a water bath at 60°C | - Transferred to a bath at 40°C before use as 60°C is too hot for patient
44
How is agar cooled?
Cooled by water circulated via cooling tubes attached on outer surface of tray
45
What are some advantages of agar? (3)
- Once the equipments’ set up it is easy to use - The material is cheap - Impressions have good surface detail
46
What are some disadvantages of agar? (5)
- Impressions must be cast up immediately to prevent shrinkage - Agar absorbs water during disinfection - Poor compatibility with model materials (ie stone) - Poor tear strength - Highly viscoelastic

BDS 2: Dental Materials (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions