Clinical failures

Question 1

rough or uneven impression surface

Answer 1

• incompletepolymerization
• improper mixing or ratio of components
• FOR ADDITION SILICON= surface agents like latex contaminate material and inhibit polymerization
• FOR CONDENSED SILICON= excessively high accelerator/base ratio with

Question 2

bubbles

Answer 2

air incorporated when mixing

Question 3

irregularly shaped voids

Answer 3

moisture or debris on surface of teeth

Question 4

rough or chalky stone cast

Answer 4

• inadequate cleaning of impression
• excess water still present
• excess wetting agent still on impression
• premature removal of caste
• improper W/P ratio
• ADDITION SILICON= failure to delay pour for at least 20 minutes (so it doesn’t contain salt?)

Question 5

distortion

Answer 5

*movement of tray during polymerization
*resin tray not aged sufficiently
*lack of adhesion of elastomer to tray
*excessive bulk of materiel used
*elastic properties develop in material before tray is set
*premature or improper removal of impression from mouth
delayed pouring of addition silicone or condensed silicon impression
*lack of mechanical retention to impression tray

Question 6

Inadequate bulk causes what?

Answer 6

Tearing

Question 7

Leaving case in impression too long causes what?

Answer 7

Rough or chalky cast

Question 8

Having a too low W/P ratio causes?

Answer 8

Grainy material

Question 9

Impression not poured immediately causes?

Answer 9

Distortion

Question 10

Air incorporation during mixing causes?

Answer 10

Bubbles