Week 4- Accurate Impressions Flashcards
What factors are involved in taking an accurate impression?
- Material selection
- Tissue and tooth preparation management
- Tray selection
- Retraction
- Haemostasis
- Impression techniques
- Bite registration
- Infection control/disinfection
What details is alginate good for recording?
Alginate is good for recording teeth detail but doesn’t produce compression of tissues.
If you have pt with resorbed lower ridge, what material should be used and why?
If you have resorbed lower ridge, use PVS instead. Thick material pushes tissues out of the way so lab tech can make correct special tray. If first impression is underextended, the final denture will end up being underextended
What is the issue with plastic trays?
Plastic trays flex which can lead to impression distorting.
What adrenaline amount is a ½ inch of cord equivalent to?
Adrenaline in 2.5cm piece of cord contains slightly less than amount of adrenaline in 4 lignocaine cartridges
What are important features to look for in impression?
- Setting time
- Homogenous mix
- Sufficient amount of material
- Complete coverage with adhesive
- Rigid impression tray
- Accurate margins
- High elasticity and dimensional stability
Where is it important to not have voids/pulls in impression material?
Margin of crown prep
How long is required for denture adhesive to stick on tray before placing impression material?
Need to allow 5-10 minutes
What is Hooke’s law?
Extension vs load applied is directly proportional until you exceed elastic limit. At this stage, the material no longer elastically recovers.
What are desirable qualities of impression materials?
- Pleasant odour
- Affordable
- Easy to use
- Adequate strength
- Accurate
- Readily disinfected without loss of accuracy
- Thixotrophic
Why is light body a different colour to tray material?
Give visual contrast to see margins of preparation.
What is thixotrophic?
When squirting material, it flows under pressure.
What is a closed bite impression tray (triple tray or dual arch)?
Prepared arch and opposing arch are taken together so jaw relation and impression can be taken at same time.
What are the disadvantages of triple trays?
- Flexible
- Impression likely to distort.
- No cross-arch stabilization
- May distort the impression material if teeth contact opposing arch or bite side walls of tray, or back plastic of tray
What are tooth requirements for triple trays?
Triple tray must always have teeth on either side of preparation.