Impressions for complete dentures Flashcards
Define the aim of primary impressions.
Accurately record relevant clinical landmarks without excessive tissue distortion.
What are primary impressions used for?
- treatment planning
- construction of special trays
Describe the properties of a stock tray.
- plastic usually
- perforated usually
- some in variety of sizes (may need adjusted if between sizes)
What is the difference between dentate and edentate trays?
Edentate trays are much shallower as they don’t have to accommodate teeth.
What can be used to modify stock trays?
- putty
- soft red wax
- red composition
- greenstick
What are the properties of putty?
- silicone based
- expensive
- longer setting time
What are the properties of soft red wax?
- cheap
- manipulate easily in hands
- poor dimensional stability
What are the properties of red composition?
- cheap
- requires boiling water to manipulate
- short working time
- thermoplastic
What are the properties of greenstick?
- cheap
- requires intense heat to manipulate
- tricky to manipulate
- runny
What do you use to reduce the extension of a stock tray?
- acrylic bur
- straight handpiece
Where is it common to reduce stock trays?
- mandibular tori
- labial and lingual frenum
- muscle attachments buccally
- palate
What impression material is most commonly used for primary impressions?
Alginate
What is a good alternative material for primary impressions in patients who retch?
Red composition
What is the ideal spacing between the tray flange and denture bearing area?
4mm
How do you border mould in the lower impression?
Ask patient to stick tongue out to record correct sulcus depth
What should be assessed when deciding whether an impression is acceptable?
- all edentulous areas included?
- sulci areas recorded fully?
- any air blows?
- fit for purpose?
What is the aim of master impressions?
Record denture bearing area, functional depth and width of sulci
What are master trays made from?
- VLC resin PMMA
- pre-rolled sheets are moulded to the primary impressions
What spacing is required for master trays when using alginate as the impression material?
3mm
What spacing is required for master trays when using silicone elastomers as the impression material?
3mm
What spacing is required for master trays (replica technique) when using silicone elastomers as the impression material?
No spacing
What spacing is required for master trays when using ZOE as the impression material?
No spacing
