Biomaterials Exam - Impression Materials Flashcards

(29 cards)

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?

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?

19
Q

Do polyethers have good or bad dimensional stability?

20
Q

With what is gypsum cured?

21
Q

Through what process is gypsum dehydrated?

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?

25
How is Triad (denture base material) cured?
visible light cured (VLC)
26
How are provisionals cured?
chemically cured (by mixing)
27
Why is there a difference in composition between denture bases and provisionals?
- 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
Are mouth guards made of thermoplastic or thermoset material?
thermoplastic | low softening point, thermally processed with hot water, vacuum formed so it required a dye
29
What controls the properties of the thermoplastic mouth guard material?
copolymer of ethylene and acetate