Elastomeric impression materials (elastomers) Flashcards
What is an elastomer?
A polymer with elastic (rubber-like) properties
Elastomers can be natural or synthetic - which are only used in dentistry?
Synthetic
In what form do elastomeric impression materials come? Explain
Liquid polymers (pre-polymers (short chains thin grow via polymerisation or cross linking)
Elastomers often have repeating units of Si-O or C-O
Why is this better than C=C?
More flexible
Why is filler added to liquid polymers?
Make a paste
What property of the liquid polymer makes the elastomer?
Crosslinking
Why were elastomers developed in terms of addressing problems with alienates?
Alginates not accurate enough for crown and bridge work
Large dimensional changes
poor tear resistance - problems in thin sections
Name 2 useful elastomers?
Silicones
Polyether
By what reaction are condensation silicone elastomers formed?
Condensation reaction
Describe the condensation reaction to form silicones?
a) reactors
b) catalyst
c) setting reaction
d) initial and final characteristic
e) by-product
a) silicone prepolymers and silica to from paste
b) tin
c) chain extension and cross linking
d) fluid to elastic
e) alcohol
Significance of alcohol by product in silicone setting reaction?
Significant dimensional changes over time - pour cast as soon as possible
Why are addition silicones used more than condensation silicones?
Less dimensional changes
What are the 3 paste systems that addition silicones come in?
Hand mixed
Cartridge - expensive, more waste
Mechanical mixers - even more expensive and more waste
Advantages of addition silicones?
Addition reaction = no-by product = no dimensional changes
Why wait a certain amount of time before pouring the impression of addition silicones?
hydrogen may be evolved - form pits