JVD 2013 #2 - FOUNDATIONS - Dental Impression Materials Flashcards

1
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

Which impression materials are inelastic?

A

Impression compund

impression plaster

ZOE

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2
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

Which impression materials are elastic, but not elastomeric?

A

agar hydrocolloid

alginate hydrocolloid

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3
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

Which impression materials are elastomeric?

A

polysulfide

condentsation silicone

polyether

addition silicone (PVS/VPS)

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4
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

to what level of detail does the ADA specify elastomeric impressions must record?

Which material is the most effective in this regard?

A

25 um

polyvinyl siloxane

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5
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

What level of detail do heavy body materials have to record?

A

75 um

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6
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

What is the limiting factor with regards to accuracy of replication?

A

ability of gypsum materials to reproduce detail in the impression

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7
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

What is elastic recovery?

A

ability of a material to return to it’s original shape after removal (i.e. from an undercut)

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8
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

What is dimensional stabilty and what materials possess the best?

A

ability of a material to maintain accurate dimensions over time

PVS - has no byproduct when setting, so maintains shape best.

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9
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

What processes affect the dimensional stability of alginates over time?

A

syneresis (evaporation of water)

imbibition (absorption of water)

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10
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

How long should alginate be wrapped in a moist towel before pouring models?

A

<1 hour, especially older materials

(some newer materials can be poured up to 100 hours after taking impression)

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11
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

What is a thixotropic material?

A

viscous under normal conditions but become less viscous allowing better flow when stressed or agitated (or pushed through a syringe).

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12
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

What material is the most flexible?

A

Alginate

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13
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

Which of these two materials displays better wettability?

A

material A

When they talk about wetting angles, they mean the angle at the external interface between the droplet and the surface.

wetting angle of 0 would be perfect wetting, and angle of 180 would be no wetting (material would be a perfect sphere sitting on the surface and a single tiny point of contact)

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14
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

What is the main problem with agar hydrocolloids?

A

need special cooled impression trays to allow the material to set

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15
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

What is the chemical reaction in the setting of alginate?

A

A sodium or potassium alginate salt will dissolve in water,

which then reacts with calcium sulfate present in the powder

to form insoluble calcium alginate that is the set impression material

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16
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

Why is sodium phosphate added to alginate materials?

A

•sodium phosphate as a retarder to preferentially react with soluble calcium ions. slows reaction down because calcium alginate isn’t formed until the sodium phosphate is exhausted.

17
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

What is the difference between type I and type II allginate?

A

Type I - fast set - form a gel in 1-2 minutes

Type II regular set - form a gel in 3-4 minutes

18
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

What are disadvantages of polyether materials?

A

very rigid,

short working time

absorb water from the atmosphere, need to pour within 30 mins

19
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

what is the difference between addition silicomnes (like PVS) and condensation silicones?

A

condensation silicones give off ethyl alcohol while setting, contributes to shrinkage

addition silicones give off no by-product, and this contribute to dimensional stability

20
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

What is the chemical reaction in addition silicone like PVS?

A

reaction is between terminal hydrogen and vinyl groups in the presence of a platinum catalyst.

Although hydrogen is produced, this is scavenged by the platinum.

No byproduct given off after setting.

21
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

what is the elastic recovery of PVS?

A

99.8%

22
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

What is a major disadvantage of PVS material?

A

It is hydrophobic, making it difficult to take impressions and pour stone

23
Q

According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,

What is the advantage and disadvantage of light wash PVS materials?

A

•The lower the viscosity, the higher the surface detail reproduction, but the greater the polymerization shrinkage.