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Operative Midterm 2 > Impression Materials, Gypsum, Mouthguards, and Tray Materials > Flashcards

Impression Materials, Gypsum, Mouthguards, and Tray Materials Flashcards

1
Q

What are 2 water based impression materials?

A

Alginates and agar-agar

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2
Q

What feature of water based impression materials allows them to wet tooth structure and gypsum?

A

They are hydrophilic

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3
Q

What is the actual name for alginate impression material?

A

Irreversible hydrocolloid impression material

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4
Q

Alginate impression material is used to make dental impressions for what?

A

Removable partial dentures, preliminary impressions for complete dentures, orthodontic study models and study models

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5
Q

What are alginate impressions not used for in the mouth?

A

Crown and bridge impressions (lack of accuracy)

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6
Q

Alginic acid is soluble in water and forms what when it is mixed with water?

A

Sol

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7
Q

What is sol?

A

Resembles a solution, but is made up of colloidal particles dispersed in a liquid

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8
Q

What are the reactants for irreversible hydrocolloid impression material?

A

Sodium or potassium alginate (12-15%), calcium sulfate dihydrate (8-12%)

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9
Q

What is a retarder for irreversible hydrocolloid impression material?

A

Sodium phosphate (2%)

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10
Q

What is the reinforcing filler for irreversible hydrocolloid impression material?

A

Diatomaceous earth (70%)

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11
Q

What are the two main chemical reactions of irreversible hydrocolloid impression material?

A

1st: provides adequate working time (retarder)
2nd: after the sodium phosphate has reacted, remaining calcium sulfate reacts with sodium alginate to form an insoluble calcium alginate, which forms a gel with the water

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12
Q

What is syneresis?

A

Loss of water to the surroundings

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13
Q

What is imbibition?

A

Pick up water from the surroundings

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14
Q

What is dimensional stability of alginate impressions?

A

Because it is a gel, it undergoes shrinkage or expansion upon loss or gain of water

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15
Q

What is the main advantage of hydrophobic impression materials?

A

They provide better stability

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16
Q

What is the main disadvantage of hydrophobic impression materials?

A

They do not wet tooth structure or gypsum well

17
Q

What is type I gypsum?

A

Impression plaster or mounting plaster

18
Q

What is type II gypsum?

A

Laboratory plaster or model plaster

19
Q

What is type III gypsum?

A

Laboratory stone, dental stone, or quick stone

20
Q

What is type IV gypsum?

A

Die stone

21
Q

Laboratory stone and die stone are what kind of gypsum plaster?

A

High strength plaster

22
Q

What is gypsum?

A

The dihydrate form of calcium sulfate CaSO4-2H2O, that is found in a compact mass in nature

23
Q

What is calcination?

A

This is the process of driving off part of the water of calcium dihydrate to form calcium sulfate hemihydrate

24
Q

If all of the different gypsum materials are chemically identical why do they have different properties?

A

They do because of changes in the way calcination was performed

25
Q

Gypsum plaster is composed of what?

A

Beta form of calcium sulfate hemihydrate crystals

26
Q

Gypsum stone is composed of what?

A

Alpha form of calcium sulfate hemihydrate crystals

27
Q

What is type V gypsum?

A

High-strength, high-expansion dental stone

28
Q

Why is dental plaster weaker than dental stone?

A
  1. porosity of the particles, requiring more water for a plaster mix
  2. irregular shapes of particles prevent them from fitting together tightly
29
Q

About how much stronger is stone than plaster?

A

2.5X

30
Q

What is a way to improve gypsum resistance to abrasion?

A

Add gypsum hardeners like colloidal silica or synthetic resin

31
Q

What is the product triad used for?

A

Custom tray material that is visibly light cured

Operative Midterm 2 (5 decks)

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