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Dental materials > Gypsum > Flashcards

Gypsum Flashcards

1
Q

If it is fluid when poured what does it do?

A

Capture fine detail

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2
Q

What does good wetting mean?

A

Spreads easily

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3
Q

Once it is set, is it fracture resistant or prone?

A

Fracture resistant

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4
Q

What are the 5 ISO gypsum types?

A

Type 1: Impression plaster

2: Dental plaster
3: Dental stone for model/die
4: Dental stone, high strength, low expansion
5: Dental stone, high strength, high expansion

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5
Q

What properties does Type 1 impression plaster have?

A

Very fluid when poured so flabby ridges won’t be distorted

Non elastic

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6
Q

What is the equation for the formation of gypsum product?

A

Calcium sulphate dihydrate to CaSO4 hemihydrate

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7
Q

What happens as dihydrate changes to hemihydrate?

A

The water has been dried off giving off a powder

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8
Q

Gypsum can be made into dental plaster by?

A

120º

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9
Q

Gypsum can be made into dental stone by?

A

Autoclave 125º

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10
Q

Gypsum can be made into densite by?

A

Boiling in Cacl2

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11
Q

What is strongest out of plaster stone and densite?

A

Densite

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12
Q

What happens when gypsum is setting?

A

Hemihydrate back to dihydrate

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13
Q

Why should you use a vibrating plate when making moulds?

A

Lets the plaster flow better

Knocks the air out allowing the water to readily mix with the plaster.

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14
Q

What is the 1st stage in the setting reaction?

A

Water becomes saturated with hemihydrate

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15
Q

What is the 2nd stage in the setting reaction?

A

Conversion of hemi to dihydrate

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16
Q

What is the 3rd stage in the setting reaction?

A

Dihydrate crystallises which is initiated by exposure to nuclei of crystallisation (stray bits of gypsum left in the bowl)

17
Q

Explain gilmore needles

A

The gilmore needles indicates the initial set but not the FINAL set.

18
Q

What is an accelerator of gypsum?

A

K2SO4

19
Q

Does temperature have an effect on expansion?

A

No as it accelerates solution process but retards crystallisation

Dental materials (10 decks)

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