Impression material

Question 1

What are FOUR types of non-aqueous elastomers?

Answer 1

• Polysulfides
• Condensation silicones
• Polyethers
• Polyvinyl Siloxanes (PVS)

Question 2

Polysulfide:

• Reaction type and byproduct
• Disadvantages

Answer 2

• Reaction type: Condensation (SH, Pb2O)
• Byproduct: H2O
• Disadvantages: poor dimensional stability (water loss, temp change, continued polymerisation) Offensive odour

Question 3

Condensation silicones:

- Byproduct

Answer 3

• Byproduct: alcohol (smell)

NOTE: stability: PVS > condensation silicones > polysulfides

Question 4

PVS:

• Reaction type and byproduct
• Advantage
• Disadvantage

Answer 4

• Reaction type: addition
• Byproduct: hydrogen gas
• Advantage: very dimensionally stable
• Disadvantage: setting retarded by sulfur in latex gloves and astringident solutions

Question 5

Polyethers:

• Reaction type
• Disadvantages
• Advantage

Answer 5

• Reaction type: cationic polymerisation of imine end groups
• Disadvantages: very stiff, odour
• Advantage: very good shelf life (~5yrs)