DM3- Elastomeric Impression Materials Flashcards
What are the 4 types of elastomeric impression materials?
- polysulphides
- silicone rubbers (condensation curing)
- silicone rubbers (Addition curing)
- polyether
ISO 4823 classifies according to what?
- chemical nature
- consistency
what is the consistency of Putty?
- high dimensional stability
- tissue displacing
- poor dine detail capture
what is the consistency of light bodied material?
- low dimensional stability
- limited tissue displacing
- fine detail capture
What are the two pastes in polysulphides?
- base paste (white)
- catalyst past (dark brown)
what is base paste made up of?
- polysulphide
- prepolymer,
- plasticiser
- inert filler
what is catalyst paste made up of?
- PbO2
- sulfur
- inert oil
How does a polysulphide set?
condensation polymererisation
What increases as cross linking of polysulphid occurs?
viscosity and elasticity
what are the properties of polysulfides? (6)
- high tear resistance but slow incomplete elastic recovery
- heavy bodied best dimensional stability
- reaction continues with water loss
- concerns
concerning use of lead - impression easily read
- bad odour and tatse
how are silicon rubber (condensation curing) set?
- cross linking of hydroxyl terminated polydimethylsiloxane chains
what are the properties of silicon rubbers (condensation curing)?(8)
- set time less than polysulphides
- elasticity develops more rapidly than polysulphides
- hydrophobic
- tear resistance adequate
- good elastic recovery
- post setting dimensional changes so must pour soon
- handle liquid components with respect
- considered non toxic in intraoral application
In a silicone rubber condensation curing reaction what is the cross linking agent?
Alkyl silicate
In a silicone rubber condensation curing reaction what is the the catalyst?
Tin
what is the setting reaction of silicon rubbers (addition curing?
platinum catalysed addition rection
What are the properties of silicon rubber (additon curing) (3) ?
- same as condensation silicons
- no by products
- hydrophobic though new formulations incorporate surface activate agents to render more hydrophilic
how does polyether set?
cationic ring opening addition polymerisation
what happens as polyether sets?
viscosity increases resulting in a rigid cross linked rubber
what are the properties of polyether?
- relatively rigid
- lack of heavy body/putty limits use
- hydrophilic which is an issue in human environments
- allergy
- must limit immersion to 10 mins in hypochlorite
