Elastomeric impression materials Flashcards
What are polysulphides also known as?
- First dental elastomers
- Vulcanizing impression materials
- Mercaptan impression materials
- Thiokol
What colour is polysulphide?
Brown
What gives polysulphide its colour?
Lead dioxide polymer
What is the nature of the polymerization reaction of polysulphides?
Exothermic
What is the setting time of polysulphides?
8 - 12 minutes
Are polysulphides comfortable for the patient?
No. Unpleasant odour and colour. It’s messy and stains clothes.
How can you accelerate polysulphide setting time?
Heat and moisture.
Are polysulphides dimensionally stable?
No. Max permanent deformation.
How soon must cast be poured after polysulphide impression is made?
Within 30 minutes to preclude chances of deformation.
What causes dimensional change in polysulphides?
High amount of polymerisation shrinkage
What causes polymerisation shrinkage in polysulphides?
Loss of water, which is the byproduct of the polymerisation reaction.
How can polymerisation shrinkage and permanent deformation be avoided with polysulphides?
- Taking minimum quantity of impression material
2. Using a custom acrylic tray
One redeeming quality of polysulphide impression materials
Shows highest tear strength
What is the relation of polysulphide impression materials with water?
Hydrophobic. Impression area needs to be dried before making an impression with polysulphide.
What, along with high tear strength, makes polysulphides suitable for recording deep undercuts?
High flexibility - the material can be released from the undercut areas with minimum stress.
Biocompatibility of polysulphides.
Good – causes lowest cell death count.
What sets polysulphides apart from all the other impression materials?
They’re the only material that can be electroplated.
What are Room Temperature (RTV) silicones?
Condensation silicone
Which elastomeric impression material has the highest curing shrinkage?
Condensation silicone, because of evaporation of ethyl alcohol byproduct.
How soon must cast be poured after a c-silicone impression is made? Why?
30 minutes - to avoid curing shrinkage.
How is the deformation of condensation silicone compared to polysulphides?
C-silicones show less permanent deformation compared to polysulphides.
Relationship of c-silicones to water.
Hydrophobic.
Flexibility of c-silicones.
HIgher than polysulphides - can be removed from undercuts without distortion.
Shelf life of c-silicones
Limited, because of oxidation of the tin component.
