Elastomerics

Question 1

what is elastomeric impression material?

Answer 1

• derived from industrial applications
• often the solution to the main hydrocolloid problems
  (poor tear resistance and dimensional stability)

Question 2

what are the 4 types of elastomeric

Answer 2

• polysulphides (not used anymore)
• silicone rubber (condensation curing)
• silicone rubber (addition curing)
• polyether

Question 3

how does ISO classify elastomeric materials?

Answer 3

based on their chemical natures and consistency

• type 0: very high consistency, putty-like
• type 1: high consistency, heavy bodies
• type 2: medium consistency, medium-bodied
• type 3: low consistency, light-bodied

Question 4

what are the 2 pastes of polysulphides

Answer 4

• base paste (white)

- catalyst paste (brown)

Question 5

what is the setting reaction for polysulphides

Answer 5

condensation polymerisation

Question 6

true or false?

as cross-linking occurs, viscosity and elasticity increases.

Answer 6

True

Question 7

state the properties of polysulphides

Answer 7

\+ heavy-bodied 
\+ reaction continuous with water loss 
\+ impression easily read
- concerns with the use of lead
- bad taste and odour 
- time to set is 10 mins

Question 8

what are the 2 pastes of silicone rubber (condensation curing)

Answer 8

• 2 pastes or paste and liquid
• paste 1: inert filler such as silica
• paste 2/liquid: alkyl silicate and tin compound

Question 9

what is the setting reaction for silicone rubber (condensation curing) and state the role of tin and alkyl silicate in this process

Answer 9

• cross-linking
• alkyl silicate acts as cross-linking agent
• tin compound as catalyst
• C2H5O11 as by product

Question 10

state the properties of silicone rubber (condensation curing)

Answer 10

• set time less than polysulphides
• elasticity more rapidly developed
• tear resistance adequate
• non-toxic
• good elastic recovery
• post dimensional changes so must pour soon

Question 11

what are the 2 pastes of silicone rubber (addition curing)

Answer 11

• paste 1: filler, catalyst, liquid silicone prepolymer

- paste 2: filler, liquid silicone prepolymer

Question 12

what are the available viscosities of silicone rubber (addition curing)

Answer 12

• putty
• heavy-bodied
• regular
• light

Question 13

what is the setting reaction for silicone rubber (addition curing)

Answer 13

• addition polymerisation
• platinum as a catalyst
• no by-products

Question 14

what are the 2 pastes of polyethers?

Answer 14

• base 1 (larger tube): inert filler

- base 2(smaller tube): reaction initiator

Question 15

what is the setting reaction for polyether

Answer 15

• addition polymerisation
• no by-products
• as it sets, viscosity increases, resulting in rigid cross-linking numbers

Question 16

what are the properties of polyether

Answer 16

• relatively rigid
• similar tear resistance to silicone rubbers
• lack of putty/heavy body limits use
• hydrophilic (not good for humid environments)
• allergy