Impressions for Complete Dentures

Question 1

What are primary impressions used for?

Answer 1

Treatment Planning
Construction of special trays

Question 2

What are the clinically relevant landmarks in taking upper impressions?

Answer 2

Hard palate
Ridge crest

Question 3

What are the clinically relevant landmarks in taking lower impressions?

Answer 3

Buccal shelf
Pear-shaped pad

Question 4

What materials can be used to modify stock trays?

Answer 4

Putty
Soft red wax
Red composition
Greenstick

Question 5

Describe red composition?

Answer 5

Cheap
Requires boiling water
Less available in practice
Very short working time

Question 6

Describe putty

Answer 6

Expensive
Quick setting time

Question 7

Describe soft red wax

Answer 7

Cheap
Can manipulate easily in hands
Poor dimensional stability

Question 8

Describe greenstick

Answer 8

Cheap
Rarely used in stock trays
Requires intense heat
Tricky to manipulate
Runny so better suited for smaller additions on special trays - used frequently for extending a special tray

Question 9

How can the extension of stock trays be reduced?

Answer 9

A straight handpiece with an acrylic bur

Question 10

What are the limitations of stock trays?

Answer 10

Not made to measure
Peripheral extensions often over or under extended
Limited sizes available
Require master impressions to record denture bearing area with accuracy

Question 11

Why is red composition sometimes used instead of alginate?

Answer 11

Used in retching patients
Rapid working time - seconds rather than minutes

Question 12

What should be asked when assessing a primary impression?

Answer 12

Are all edentulous areas included?
Are the sulci areas to be included in the denture recorded fully?
Are deficiencies present due to air bubbles?
Is the impression fit for purpose or not?

Question 13

If an impression is to be repeated, how can it be improved?

Answer 13

Tray modification
Amount of material
Tray placement
Was border moulding sufficient?
Do i need to pre-pack palate/tuberosities?
Can the patient cope with a repeat impression today?

Question 14

What happens when taking master impressions?

Answer 14

Denture bearing area, functional depth and with of sulci are recorded
Use custom made special trays prescribed after primary impressions

Question 15

What materials can special trays be made of?

Answer 15

VLC resin PMMA (acrylic)
Self-cure PMMA (acrylic)

Question 16

What are the advantages of special trays?

Answer 16

Accurate peripheral extension
Uniform thickness of material
Reduced amount of material - less discomfort as tray fits individual mouth
Records denture bearing area more accurately

Question 17

What should you aim for in master impressions?

Answer 17

Well rounded borders
Minimal air blows and none in important areas
Impression centrally placed in tray
Ensure all clinically relevant areas are included

Question 18

What are common mistakes made when taking master impressions?

Answer 18

Obvious differences between sulcus width on either side
Under extended tray leads to underextended impression
Incomplete tray seating
Sharp border to lingual pouch
Overextended tray leads to overextended impression