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Yr 2 DM > DM8 - Alginates > Flashcards

DM8 - Alginates Flashcards

1
Q

what are the 3 main impression materials

A

Hydrocolloids
Elastomers
Non-elastic materials

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2
Q

what are the 2 types of hydrocolloid impression materials

A

Reversible agar

Irreversible alginates

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3
Q

what are the 3 types of non-elastic material, elastic impression materials

A

zinc oxide eugenol
impression plaster
impression compound

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4
Q

what are the 3 types of elastomers in impression materials

A

silicones
Polysulphides
polyethers

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5
Q

what are the 2 types of silicones for elastic impression materials

A

condensation

addition

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6
Q

why are alginates classed as irreversible hydrocolloids

A

sets by a chemical cross-linking reaction

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7
Q

what is alginate made from

A

extracted from seaweed with hydroxide

NaOH forms sodium alginate

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8
Q

what happens when alginate is mixed with water

A

forms colloidal suspension

sets by chemical cross linking reaction (irreversible hydrocolloid)

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9
Q

what are the 6 things in alginate powder composition and what are their functions

A

◆Na/K alginate 12%
◆ diatomaceous earth (filler - body/strength) 70%
◆ CaSO4 (cross-linking agent) 12%
◆ Na3PO4 (or Na2CO3) (retarding agent) 2%
◆ Sodium silicofluoride or Sodium fluorotitinate (pH controller) 4%
◆ Magnesium oxide
(pH controller) 3%

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10
Q

what is the function of diatomaceous earth in the composition of alginate powder

A

filler - body/strength 70%

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11
Q

what is the function of CaSO4 in the composition of alginate powder

A

cross-linking agent 12%

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12
Q

what is the function of Na3PO4 (or Na2CO3) in the composition of alginate powder

A

retarding agent 2%

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13
Q

what is the function of Sodium silicofluoride or Sodium fluorotitinate in the composition of alginate powder

A

pH controller 4%

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14
Q

what is the function of magnesium oxide in the composition of alginate powder

A

pH controller 3%

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15
Q

where does cross linking during the setting stage occur within the sodium alginate powder

A

polymer chain

chemical bonds joining 2 polymer chains by Ca

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16
Q

explain what happens for the setting reaction to occur (function of cross-linker + retarder)

A

look at ipad for notes

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17
Q

why are pH controllers added to alginate mix

A

water + alginate -> pH12
setting = pH 3 –> once set pH9
◆ ↑ alkalinity + acidity give poor plaster/stone surface
◆ pH controller ↓ pH to 8 (near neutral) so its compatible with casting materials
◆ improves surface of resulting gypsum cast (mould)

18
Q

what are the ph controllers used in alginates

A 
sodium silicofluoride (or fluorotitinate) 
MgO
19
Q

how is chromoclone linked to pH controllers

A

purple = water + alginate
pink = mixed well + loaded into tray
light peach = insert tray into mouth
◆ prevents unnecessary time in oral cavity

20
Q

what is the mix time for chromoclone alginate

A

90-110 secs

21
Q

what are the advantages of using alginates

A

good setting behaviour
◆ Na3PO4 (retarder) suppresses setting at first
◆ material - viscous paste while tray is in mouth
◆ once setting starts, completed real quickly -> ↓ impression time

material is cheap + reliable

22
Q

what are the 5 main disadvantages of using alginates

A
  1. alginates in air loses water
  2. alginate must be immersed in water/disinfecting solution
  3. poor tear strength
  4. ↑ viscoelastic material
  5. doesn’t adhere well to tray
23
Q

how is it a disadvantage of alginate that in air it loses water?

A

◆ continual shrinkage in air (so need immediate casting, but its not practical)
◆ poor dimensional stability in air
◆ impression must be covered in damp napkin/gauze + plastic bag, sealed

24
Q

how is it a disadvantage of alginate that it needs to be immersed in water/disinfecting solution?

A

◆ initially swells, then shrinks IMBIBITION
◆ poor dimensional stability in solutions
-> so must follow disinfection protocol

25
Q

how is it a disadvantage of alginate that it is high viscoelastic material?

A

◆ snap-removal technique needed

Technique sensitive

26
Q

how is it a disadvantage of alginate that it doesn’t adhere well to the tray?

A

◆ retention to tray by mechanical locking features

◆use perforated trays or apply adhesive

27
Q

what is the disinfectant protocol for alginates

A
  1. remove alginate from mouth
  2. rinse in tap water -> removes blood/saliva
  3. Immerse in disinfecting solution for ONLY 10MINS
  4. Remove from solution + rinse in water
  5. wrap in damp napkin/gauze + seal in polythene bag
28
Q

how do you properly dispense alginates + why needed

A

◆ density of diff ingredients in powder differ
◆ shaken before use, let dust settle 2mins before use
◆ silica particles in dust can be health hazard

29
Q

what do you add to get dust free alginate

A

small amount ethylene glycol

30
Q

what are the 3 types of alginates you can get

A

◆Fast
◆regular
◆slow set
depending on amt of retarder and cross-linking agent

31
Q

why is agar classed as a reversible hydrocolloid

A

sets by physical process

32
Q

what states does agar exist at

A

◆ solid gel at room temp
◆ viscous liquid at 60°C
◆ cooling - gelling = physical process

33
Q

what are the 5 things in the composition of agar and their functions

A
  1. Agar (colloid) 13-17%
  2. Borates (strengthen gel)
  3. potassium sulphates (accelerates setting of stone)
  4. thixotropic materials - wax (filler)
  5. water (dispersion medium)
34
Q

what is the function of agar in the composition of agar impression materials

A

colloid 13-17%

35
Q

what is the function of borates in the composition of agar impression materials

A

strengthen gel 0.2-0.5%

36
Q

what is the function of potassium sulphates in the composition of agar impression materials

A

accelerates setting of stone 1-2%

37
Q

what is the function of thixotropic materials (wax) in the composition of agar impression materials

A

filler 0.5-1%

38
Q

what is the function of water in the composition of agar impression materials

A

dispersion medium

39
Q

how do you dispense agar

A

◆ tubes - prevent water loss
◆ Tubes in water bath at 60% (liquid) -> bath at 40% before use
◆ Material squeezed out onto special metal tray in mouth
◆ Tray cooled by water (tubes attached on outer surface)

40
Q

what are the 3 advantages of using agar

A

◆ set up, easy to use
◆ Cheap material
◆ Impressions have good surface + fine detail -> due to setting behaviour

41
Q

what are the 4 disadvantages of using agar

A

◆ Impressions cast immediately - avoids shrinkage due to synerisis
◆ Absorbs water (imbibition) - can distort impression
◆ Poor tear strength but better than alginates
◆ Highly viscoelastic so technique sensitive; snap-removal technique

Yr 2 DM (5 decks)

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