Quiz 2 Flashcards by Aliyah Bennett

To reproduce the form of teeth and surrounding oral tissue

Diagnostic cast

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Replica of prepared tooth

Die

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What is the negative reproduction?

Completed impression

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What is the positive reproduction?

Final model

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What are the 3 types of impressions?

Preliminary
Final
Bite registration

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 Checking for proper relationship of opposing teeth/restorative work
 Aids with articulating models accurately

Bite registration

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What are the types of impression materials?

Elastic & inelastic

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What are examples of elastic materials?

Alginate
Agar
Polysulfides
Silicone rubber
Polyether

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What are examples of inelastic materials?

Dental compound
impression plaster
ZOE
Wax

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What are the key properties of impression materials?

Accuracy
Tear resistant
Dimensional stability

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o Water-based, substance suspended in solution
o Elastic impression material

Hydrocolloids

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reversible hydrocolloid, physical reaction occurs allowing to go from sol to gel and back to sol

Agar

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Liquid suspension

Sol

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Semisolid after chilling

Gel

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irreversible hydrocolloid, chemical reaction occurs which prevents from reversing back to gel when heated

Alginate

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 Working time: 2-3 mins from mix to mouth
 Set time: 2-5 minutes

Regular set of alginate

 Working time: 1.25-2 mins
 Setting time: 1-2 mins

Fast set of alginate

Calcium sulfate dihydrate + sodium alginate =

Calcium alginate

What are the alginate properties?

Permanent deformation
Dimensional stability
Tear strength

What is the acceptability criteria for impressions?

o All structures covered
o Sufficient detail
o Smooth surface
o Minimal voids
o No distortion
o No debris

What is another name for rubber materials?

Elastomers

What are the 4 types of elastomers?

 Polysulfides
 Condensation silicones
 Addition silicones
 Polyether’s

What are the most popular elastomers?

polyvinyl siloxane
polyether

o More accurate than alginate
o Not water-based
o Hydrophobic, poor wettability

Elastomers

forming polymers by joining monomers end-to-end

Polymerization

o Undergoes addition reaction of polymerization o High elastic recovery and tear strength o Used frequently for bite registrations o Most are hydrophobic

Polyvinyl siloxane

o Good for crowns & bridges o More hydrophilic than PVS o More flexible in recent years o Block out undercuts

Polyether

What water retards the alginate set?

Cold

What water accelerates the alginate set?

Warm

Increase in water, swelling

Imbibition

Decrease in water, shrinking

Syneresis

-Light-bodied gel + thick tray gel -Improved detail over traditional alginate -Useful for partial/full denture impressions

2-Consistency alginate system

What require additional training?

Digital impressions

What is the maximum amount of time an operator should take to achieve a homogenous mix of regular-set alginate?

45 seconds

What is the phenomenon of gel contracting and losing water when left in a low humidity environment? -Shrinking

Syneresis

What is the phenomenon of a gel taking on more water and expanding when left in high humidity environment?

Inhibition

What will NOT result in poor tear strength of alginate?

Snapping, swift removal of impression

What is the best impression material to use for fabrications of a crown or bridge?

Polyvinyl siloxane