JVD 2013 #2 - FOUNDATIONS - Dental Impression Materials Flashcards
According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,
Which impression materials are inelastic?
Impression compund
impression plaster
ZOE
According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,
Which impression materials are elastic, but not elastomeric?
agar hydrocolloid
alginate hydrocolloid
According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,
Which impression materials are elastomeric?
polysulfide
condentsation silicone
polyether
addition silicone (PVS/VPS)
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?
25 um
polyvinyl siloxane
According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,
What level of detail do heavy body materials have to record?
75 um
According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,
What is the limiting factor with regards to accuracy of replication?
ability of gypsum materials to reproduce detail in the impression
According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,
What is elastic recovery?
ability of a material to return to it’s original shape after removal (i.e. from an undercut)
According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,
What is dimensional stabilty and what materials possess the best?
ability of a material to maintain accurate dimensions over time
PVS - has no byproduct when setting, so maintains shape best.
According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,
What processes affect the dimensional stability of alginates over time?
syneresis (evaporation of water)
imbibition (absorption of water)
According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,
How long should alginate be wrapped in a moist towel before pouring models?
<1 hour, especially older materials
(some newer materials can be poured up to 100 hours after taking impression)
According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,
What is a thixotropic material?
viscous under normal conditions but become less viscous allowing better flow when stressed or agitated (or pushed through a syringe).
According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,
What material is the most flexible?
Alginate
According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,
Which of these two materials displays better wettability?
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)
According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,
What is the main problem with agar hydrocolloids?
need special cooled impression trays to allow the material to set
According to FOUNDATIONS - Dental Impression Materials, Rachel Perry,
What is the chemical reaction in the setting of alginate?
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