impression materials and techniques

Question 1

What type of impression material tends to be used for crown and bridge work?

Answer 1

Elastomeric impression material

Alginate is not preferred for fixed prosthodontics.

Question 2

name 2 types of hydrophilic impression materials

Answer 2

irreversible - alginate
reversible - agar

Excellent for some applications but not for fixed prosthodontics.

Question 3

What are disadvantages of alginate as an impression material?

Answer 3

Must be poured within 24 hours
requires correct tray
easily distorted

Requires a correct tray and is easily distorted.

Question 4

why is agar no longer used

Answer 4

requires a cooling system

Not commonly used anymore due to the need for a cooling system.

Question 5

are elastomeric impression materials hydrophilic or hydrophobic?

Answer 5

hydrophobic

Question 6

name 3 types of elastomeric impression materials

Answer 6

silicones
polysulphides
polyethers

Question 7

What are the advantages of addition cured silicones?

Answer 7

• Very accurate
• Stable for up to 2 years
• Can be disinfected

Must wait at least an hour before casting.

Question 8

disadvantages of condensation cured silicones?

Answer 8

Less accurate than addition cured silicones
Must leave 24hrs before casting die

Must leave 24 hours before casting die.

Question 9

name an advantage of condensation cured silicones to addition cured

Answer 9

cheaper

Question 10

advantages polysulphides as an impression material?

Answer 10

Long working time, great for big undercuts

Often used for removable prosthetics but has an unpleasant smell.

Question 11

disadvantage of polysulphides as an impression material

Answer 11

smell bad

Question 12

advantages of polyethers 2

Answer 12

very accurate
less hydrophobic

Question 13

disadvantages of polyethers 2

Answer 13

Very stiff on removal
bad taste

Can complicate use for undercuts or periodontal patients.

Question 14

What are the steps in the 1 stage putty wash impression technique?

Answer 14

• Putty in tray, wash around tooth
• Wait for wash to set before putty

If the putty marks with a fingernail, it is not set.

Question 15

What is the two-stage impression technique?

Answer 15

• Put putty on tray with polythene spacer
• Remove spacer after setting
• Apply wash around prep and into putty space

Rarely done due to complexity.

Question 16

what is the mono phase impression technique

Answer 16

Monophase in syringe and tray then put one on top of the other

Question 17

What is the biological width?

Answer 17

The distance between the gingival margin and the alveolar bone

Important to avoid encroachment to prevent gingival inflammation.

Question 18

What can be done if it’s impossible to avoid encroaching on biological width?

Answer 18

Consider surgical crown lengthening

This can help manage potential inflammation.

Question 19

How does aging affect the interdental papilla?

Answer 19

Leads to black triangles due to recession

Crowns can be used to fill these spaces effectively.

Question 20

What method can be used to retract gingivae for better impressions?

Answer 20

Use retraction cord or clay containing aluminium chloride

This helps stop gingival bleeding.

Question 21

what is done to remove gingival tissue?

Answer 21

electrosurgery

Question 22

What is a risk associated with electrosurgery?

Answer 22

Can cause necrosis if it touches bone

Not recommended for patients with pacemakers.

Question 23

in what pt can electrosurgery NOT be done?

Answer 23

pacemaker

Question 24

What is the disinfection protocol for impressions?

Answer 24

10 x 1.7g Actichlor tablets per 1 litre of water for 3 minutes

Ensures safety and sterility of impressions.