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BDS3 Dental Materials > Alginate > Flashcards

Alginate Flashcards

1
Q

What is alginate?

A

irreversible hydrocolloid

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2
Q

colloid?

A

substance which is distributed evenly through another material

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3
Q

Two phases of alginate?

A

dispersed

continuous

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4
Q

What can alginate exist as?

A

either viscous liquid (sol) or as a solid (gel)

changes from solid to gel in the case of alginate

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5
Q

2 components of alginate?

A

powder and liquid

mixed into paste

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6
Q

What phase is alginate when it is a paste?

A

sol phase

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7
Q

What phase is alginate when it sets?

A

gel phase

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8
Q

composition of alginate?

A

sodium and potassium salts + alginic acid

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9
Q

What constituent of alginate dissolves in water to form a hydrogel with calcium?

A

potassium alginate or sodium alginate

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10
Q

Role of potassium alginate or sodium alginate?

A

What constituent of alginate dissolves in water to form a hydrogel with calcium

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11
Q

What slows down the setting reaction of alginate?

A

sodium phosphate

acts as a retarder by preferentially reacting with calcium ions

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12
Q

Role of calcium sulphate dihydrate?

A

reacts with soluble alginate to form insoluble calcium alginate

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13
Q

setting reaction of alginate?

A
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14
Q

What is the general term for the alginate setting reaction?

A

double decomposition reaction

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15
Q

What acts as a retarder by preferentially reacting with calcium ions?

A

sodium phosphate

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16
Q

When is the material set?

A

once the phosphate ions have been used up

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17
Q

pH change of the material upon setting?

A

11 -> 7

18
Q

mixig time of alginate?

A

45-60 secs

19
Q

working time of alginate?

A

45s (fast set)

75s (regular set)

20
Q

setting time of alginate?

A

1-4.5 mins

can be variable to altering water temp

21
Q

What occurs hewn you remove alginate form the mouth?

A

impression material compressed when removed

distortion results which could be significant

remove quickly from mouth - snap out

22
Q

How to minimise distortion of impression?

A

reducing the amount of compression

reducing the rime the impression is under compression

allowing time for recovery before poring - decompress

23
Q

Alginate and syneresis?

A

gel contracts on standing and exudes liquid

lose moisture form impression - distortion

  • need to control relative humidity and proper storage important
24
Q

How to minimise syneresis?

A

lose moisture form impression - distortion

  • need to control relative humidity and proper storage important
25
Q

imbition of alginate?

A

takes up water and swells

uncontrolled in extent and direction

26
Q

How to overcome imbition and syneresis?

A

wrap in damp tissue and store in sealed polythene bag until the impression can be cast

27
Q

what effects the strength f alginate

A

variation in water volume - reduction in powder/liquid ratio will weaken gel

insufficient spatulation - ingredients not dissolved sufficiently , inconsistent chemical reaction

over-spatulation - disruption of forming calcium alginate gel and reduce strength

28
Q

tear strength of alginate?

A

tear strength poor

especially when removing from mouth

29
Q

advantages of alginate?

A

easy flow

reproducible of detail adequate

fast set

minimal tissue displacement

cheap

pt tolerance good

30
Q

disadvantages of alginate?

A

poor dimensional stability

poor tear strength

distorts if unsupported

3mm minimum thickness requires - otherwise distortion occurs were thin sections are found, such as interproximal

easy to include air

31
Q

minimum thickness of tray?

A

3mm thickness needed for alginate impression

32
Q

indications for alginate?

A

used in situations where less accuracy/ detail is required:

study casts to pan case/design prosthesis

denture construction (primary and working impressions)

teeth opposing an indirect cast restoration

removable orthodontics appliances

other dental devised such as occlusal splints

33
Q

displace quickly or slowly form mouth?

A

quickly

34
Q

clinical tips for usage?

A

smooth impression surface

smear some material into fissures

pace some material into high palatal vault

evert lip/retract cheeks

careful not to pull tray towards dominant side

hold still in the mouth

ensure material fully set

displace quickly from mouth

35
Q

reasons for a grainy material?

A

inadequate or prolnged mixing

liquid/powder tatio too low

36
Q

reasons for tearing?

A

inadequate bulk

premature removal from mouth

37
Q

Reason for external bubbles?

A

air incorporated during mix

38
Q

reason for rough or chalky model?

A

inadequate cleaning of impression

excess water left in impression

premature removal of model

39
Q

reason for distortion?

A

delayed pouring of impression

movement of tray during impression taking

premature removal from mouth of model

40
Q

product name at IOD?

A

tropicalgin

41
Q

Steps for impression decontaminatio?

A
42
Q

Can you leave gypsum in contact with alginate for hours?

A

affect surface quality of cast

  • remove when fully set

BDS3 Dental Materials (13 decks)

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