Impressions for Complete Dentures Flashcards
What are primary impressions used for?
Treatment Planning
Construction of special trays
What are the clinically relevant landmarks in taking upper impressions?
Hard palate
Ridge crest
What are the clinically relevant landmarks in taking lower impressions?
Buccal shelf
Pear-shaped pad
What materials can be used to modify stock trays?
Putty
Soft red wax
Red composition
Greenstick
Describe red composition?
Cheap
Requires boiling water
Less available in practice
Very short working time
Describe putty
Expensive
Quick setting time
Describe soft red wax
Cheap
Can manipulate easily in hands
Poor dimensional stability
Describe greenstick
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
How can the extension of stock trays be reduced?
A straight handpiece with an acrylic bur
What are the limitations of stock trays?
Not made to measure
Peripheral extensions often over or under extended
Limited sizes available
Require master impressions to record denture bearing area with accuracy
Why is red composition sometimes used instead of alginate?
Used in retching patients
Rapid working time - seconds rather than minutes
What should be asked when assessing a primary impression?
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?
If an impression is to be repeated, how can it be improved?
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?
What happens when taking master impressions?
Denture bearing area, functional depth and with of sulci are recorded
Use custom made special trays prescribed after primary impressions
What materials can special trays be made of?
VLC resin PMMA (acrylic)
Self-cure PMMA (acrylic)
What are the advantages of special trays?
Accurate peripheral extension
Uniform thickness of material
Reduced amount of material - less discomfort as tray fits individual mouth
Records denture bearing area more accurately
What should you aim for in master impressions?
Well rounded borders
Minimal air blows and none in important areas
Impression centrally placed in tray
Ensure all clinically relevant areas are included
What are common mistakes made when taking master impressions?
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
