non elastic impression materials

Question 1

what are the properties of impression plaster

Answer 1

low strength, short setting time, dimensionally stable when cooled, minimal distortion of soft tissue–> very accurate

Question 2

what are the properties of impression compound

Answer 2

does not fracture upon withdrawal, low thermal conductivity and high COTE. minimal flow upon hardening to prevent distortion

Question 3

what are the causes of thermoplastic distortion

Answer 3

• being exposed to heat/sunlight
• improper softening
• removal of impression of mouth before evenly cooled and hardened
  – not pouring cast after impression made