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Part 3 > Impression Materials and Gypsum > Flashcards

Impression Materials and Gypsum Flashcards

1
Q

Polysulfide

  1. Primary component of polymer
  2. Filler? And what does it do?
  3. Plasticizer? What does it do?
  4. Catalyst/reactor?
  5. Accelerator?
  6. Retarder?
  7. What gives polysulfide its characteristic brown color?
A
  1. Multi-functional mercaptan (-SH) aka Polysulfide polymer
  2. Filler (titanium dioxide) - strength
  3. Plasticizer (dibutyl-phthalate) - viscosity
  4. Catalyst - lead dioxide
  5. Accelerator - Sulfur
  6. Retarder - oleic acid
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2
Q

Polysulfide

  1. What is the reaction of polysulfide?
  2. Byproduct?
  3. Does this byproduct affect any of the mechanical properties?
A
  1. Sh groups interact with oxygen released from lead dioxide
  2. Water
  3. Affects dimensional stability
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3
Q

Condensation Silicone

  1. Base paste?
  2. Catalyst
  3. What’s the reaction?
  4. By-product
A
  1. α-ω-hydroxyl-terminated poly (dimethyl siloxane)
  2. Stannous octoate
  3. The material sets by cross-linking between terminal groups of the silicone polymers and the alkyl silicate to form a three-dimensional network
  4. Ethanol molecules
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4
Q

Addition Silicone

1.Two silicone components?
2. Catalyst
3. Byproduct?
4. Why do manufacturers add a nobel metal? What noble metal?

A
  1. Polymethylhydrosiloxane and Di VPS
  2. Dimethylsiloxane polymer and Platnium salt
  3. None. But technically residual polymethylhydrosiloxane can lead to a secondary reaction with each other or moisture to produce hydrogen gas.
  4. Scavenger for released hydrogen gas. Palladium.
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5
Q

Polyether

  1. Polymer?
  2. Initiater?
  3. What makes this group of materials the most hydrophilic of elastomeric impression materials?
  4. What keeps the reaction going?
A
  1. Polyether copolymer with alternating oxygen atoms and methylene groups and reactive terminal groups
  2. Aromatic sulfonate ester
  3. Ether-dominated polymer backbone
  4. As each polymer ring opens, it then itself becomes a cation. It then attacks and opens other rings
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6
Q

Polyether
1. Second type is acid-catalyzed condensation polymerization of ___ prepolymer with ___ terminal groups

  1. Byproduct?
A
  1. Polyether prepolymer with alkoxysilane terminal groups
  2. Low molecular weight alcohols
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7
Q

Rank elastomeric impression materials by tear strength?

A

Lowest to greatest:
VPS, Polyether, Polysulfide

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8
Q

Irreversible hydrocolloid
1. Soluble alginate?
2. Reactor?
3. Filler?
4. Retarder?
5. To combat silicosis risk, alginate manufacturers add what to agglomerate the particles?

A
  1. Potassium or sodium alginate
  2. Calcium sulfate
  3. Zinc oxide or diatamaceous earth
  4. Sodium phosphate
  5. Glycol
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9
Q

What gypsum products are made under the following conditions?

  1. If gypsum is heated in open kettle at temp of 110˚C?
  2. If gypsum is dehydrated under pressure and in the presence of water vapor at ~120˚C?
  3. How are high-strength low expansion and high expansion stones made? What is their chemical name?
A

Calcining calcium sulfate dihydrate (gypsum)
Temps: 110 to 130 degrees C

  1. Plaster
  2. Model plaster (β- calcium sulfate hemihydrate)
  3. Dental stone (α-hemihydrate )
  4. High-strength dental stone
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10
Q

Why is dental stone so much denser and stronger than plaster of paris?

How is die stone made?
How are the crystals different?

A

The α-hemihydrate are more regular and not as porous. So the dihydrate produced is better packed.

Die stone: Calcinating occurs under pressure of 30% calcium chloride solution or in the presence of more than 1% sodium succinate.

Crystals: Hemihydrate crystals are shorter and thicker. Called” modified α-hemihydrate.

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11
Q

What wax compromises 40-60% of most dental waxes?
Why is gum dammar added to the above wax?
Carnauba - Three good properties?
What two natural waxes are substituted for Carnauba?

A

Paraffin - Most dental waxes 40-60%. Not smooth or glossy, so other waxes are added.
Gum dammar - Add to paraffin to improve smoothness, toughness, and luster.
Carnauba wax - Very hard, high melting point, glossy.
Candelilla - Can sub carnauba. Similar but lower melting point and hardness.
Ceresin - White wax, added for hardness, can sub with candelilla for carnauba

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12
Q

Composition Baseplate wax
Type 1, Type 2, Type 3?

A

75% paraffin/ceresin

Type 1: Building veneers
Type 2: Normal
Type 3: Tropical climates

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13
Q

Why shouldn’t you heat gypsum-bonded investment material beyond 700 degrees celsius?

What two things then occur to the casting?

A

At 700, you get significant contraction. This is due by decomposition and release of sulfur dioxide.

Results in shrinkage and contamination of the casting (with sulfides of non-noble elements like silver and copper)

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14
Q

Phillips Chapter 10, page 202

Why is Silica added to investments?

A

Gypsum normally shrinks considerably when heating. Silica can lead to expansion due to a change in crystalline form.

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15
Q

Do you typically want expansion or contraction of investment material?

What are the two principle components of gypsum-bonded investment?

A

Expansion, to compensate for the contraction of the alloy

Silica + Calcinated gypsum powder (calcium sulfate hemihydrate, or alpha-hemihydrate)

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16
Q

For gypsum bonded investment, as the water powder ratio increases (w/p = .30 to .40 and so on), what happens to expansion of the investment?

A

As W/P ratio increases, less expansion occurs of the investment.

17
Q

Phosphate-Bonded Investment
- Refractory filler?
- Binder?

A

Refractor filler: Silica (either cristobalite or quartz)

Binder: Magnesium oxide and phosphate

18
Q

1-3. Three step process for Type 4/5 stones?

  1. What is their chemical name?
A
  1. Densite is boiled in a 30% calcium chloride solution
  2. The chloride is washed away with hot water
  3. The material is ground down to the desired fineness.
  4. alpha-calcium sulfate hemihydrate
19
Q

How is Type 3 stone made?

Type 3 stones are also called:
2. (Hint, begins with a greek letter)
3. (Hint, it begins with “H”)

A
  1. Gypsum is dehydrated under pressure in the presence of water vapor at ~125˚ C.
  2. ∂-calcium sulfate hemihydrate
  3. Hydrocal
20
Q

How is dental plaster (Type 1 stones) made?

What’s the hemihydrate produced called?

A

Gypsum is heated in an open kettle at 110˚ C

ß-calcium sulfate hemihydrate

21
Q

How much µm detail are the five types of stones required to reproduce per ANSI/ADA spec No. 25

A

1-3: 75 plus or minus 8

4-5: 50 plus or minus 8

22
Q

How much µm detail are elastomeric impression materials required to reproduce?

A

20 µm per ADA spec no 19

23
Q

If typical, high strength dental stone is set in water, it has additional expansion.

How much more?
What is this called?
Why?

A
  1. From .08% to .10%
  2. Hygroscopic expansion
  3. The water allows crystals to expand further and wider

Part 3 (13 decks)

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