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AU13 - Operative Biomaterials > Biomaterials Exam - Impression Materials > Flashcards

Biomaterials Exam - Impression Materials Flashcards

1
Q

What are the requirements of ideal impression materials?

A
  • low cost
  • long shelf life
  • biocompatibility
  • pleasant to patient
  • dimensionally stable
  • good handling properties
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2
Q

What are the 3 main classes of impression materials? Name the 2 subtypes of each class.

A
  • rigid: ZOE and plaster
  • plastic: wax and compound
  • viscoelastic: hydrocolloid and elastomers
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3
Q

True or false: Alginate is an irreversible hydrocolloid impression material that is water-based.

A

true

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4
Q

What is formed when alginic acid is soluble in water?

A

sol which resembles a solution, but is made up of colloidal particles dispersed in a liquid

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5
Q

What ion cross-links alginate?

A

calcium

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6
Q

What two parameters control the setting reaction of alginate?

A
  • temperature controlled (reversible)

- chemically controlled (irreversible)

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7
Q

What is dimensional stability of alginate? How can you minimize it?

A
  • Because it is a gel, it undergoes shrinkage or expansion upon loss or gain of water.
  • minimize it by storing it in 100% humidity and by pouring quickly after removal from mouth
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8
Q

What is syneresis?

A

loss of water to the surroundings (part of dimensional stability)

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9
Q

What is imbibition?

A

pick up of water from the surroundings (part of dimensional stability)

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10
Q

What are the advantages of water-based alginate?

A
  • economical
  • easy to use
  • quick setting
  • fair taste
  • hydrophilic
  • can displace blood and saliva
  • stock trays
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11
Q

What are the disadvantages of water-based alginate?

A
  • limited detail reproduction
  • low tear resistance
  • single pour only
  • quick pouring required
  • low dimensional stability
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12
Q

Is polysiloxane impression material normally a hydrophilic or hydrophobic material?

A

hydrophobic

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13
Q

How can polysiloxane material be made hydrophilic?

A
  • adding a surfactant

- chemical incorporation of hydrophilic moieties into the silicone backbone

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14
Q

Why is the hydrophobicity of polysiloxane a problem in taking impressions and transferring detail to a model?

A
  • the oral cavity is hydrophilic so it may cause some difficulty in registering oral structure
  • when pouring the stone slurry into the impression, it may cause voids since the slurry is water-based
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15
Q

What reaction forms the cross-links of polysiloxanes?

A

hydrosilation reaction

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16
Q

Does polysiloxanes have good or bad dimensional stability?

A

good

17
Q

What is the role of a surfactant in polysiloxanes?

A

improves (along with polyethers) detail registration and detail transfer by making the polysiloxane more hydrophilic

18
Q

Of these two hydrophobic compounds (polysiloxanes and polyethers), which is more hydrophilic?

A

polyethers

19
Q

Do polyethers have good or bad dimensional stability?

A

good

20
Q

With what is gypsum cured?

A

water

21
Q

Through what process is gypsum dehydrated?

A

calcination

22
Q

What is the dehydration/rehydration reaction that is responsible for the synthesis of gypsum and the curing of it?

A

(CaSO4/0.5H2O) + 1.5H2O –> (CaSO4/2H2O) + 3900 cal/g*mol)

- hemihydrate is converted back into a dihydrate via an exothermic reaction

23
Q

The properties of gypsum are dependent on what 2 characteristics? How does this affect the gypsum?

A
  • density and crystal structure
  • if the crystals are dense, regularly-shaped, and relatively non porous, the material will not require much water and will be stronger (dental stone - alpha form)
  • if the crystals are less dense, irregularly-shaped, and porous, it will require more water to mix and the material will be weaker (dental plaster - beta form)
24
Q

Which type of gypsum (dental plaster or dental stone) is used to make dental models?

A

dental stone

25
Q

How is Triad (denture base material) cured?

A

visible light cured (VLC)

26
Q

How are provisionals cured?

A

chemically cured (by mixing)

27
Q

Why is there a difference in composition between denture bases and provisionals?

A
  • denture bases need to last a long time, have fillers, and dimethacrylates that cross-link
  • provisionals are more temporary and need to be removed, no cross-linking; chemistry is very similar to the “cold cure” Triad (denture base)
28
Q

Are mouth guards made of thermoplastic or thermoset material?

A

thermoplastic

low softening point, thermally processed with hot water, vacuum formed so it required a dye

29
Q

What controls the properties of the thermoplastic mouth guard material?

A

copolymer of ethylene and acetate

AU13 - Operative Biomaterials (6 decks)

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