Quiz 2 Flashcards
To reproduce the form of teeth and surrounding oral tissue
Diagnostic cast
Replica of prepared tooth
Die
What is the negative reproduction?
Completed impression
What is the positive reproduction?
Final model
What are the 3 types of impressions?
Preliminary
Final
Bite registration
Checking for proper relationship of opposing teeth/restorative work
Aids with articulating models accurately
Bite registration
What are the types of impression materials?
Elastic & inelastic
What are examples of elastic materials?
Alginate
Agar
Polysulfides
Silicone rubber
Polyether
What are examples of inelastic materials?
Dental compound
impression plaster
ZOE
Wax
What are the key properties of impression materials?
Accuracy
Tear resistant
Dimensional stability
o Water-based, substance suspended in solution
o Elastic impression material
Hydrocolloids
reversible hydrocolloid, physical reaction occurs allowing to go from sol to gel and back to sol
Agar
Liquid suspension
Sol
Semisolid after chilling
Gel
irreversible hydrocolloid, chemical reaction occurs which prevents from reversing back to gel when heated
Alginate
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
