W4 - Impressions - Abbott Flashcards
Important features to look for in the impression
- Impression mix should be uniform and homogenous
- Complete coverage of tray with adhesive
- Tray should not be underfilled
- Margin detail must be without voids
- Margins are free of tears
- Good recovery from deformation
Desirable qualities of impression materials
- Pleasant odour
- No taste
- No toxic or irrtitant constituents
- Affordable
- Easy to use
- Elastic properties to prevent deformation
- Adequate strength
- Accuracy
- Dimensional stability
4 types of trays
- Custom tray
- Metal - full or quadrant
- Plastic - full or quadrant
- Non-perforated or perforated
What are triple trays or dual arch trays used for
Closed bite impression
- Prepared arch and opposing arch are taken together
Risk with triple tray
Triple trays are quite flexible - can lead to potential distortion depending on the amount of material, weight of the stone, and/or type of impression material
What is an open bite impression tray
Special tray
- More rigid
- Reduces distortion and rebound effect
- Must have adhesive
- 3-4mm relief around prepared teeth
What happens if adhesive is not used
Impression shrinks toward the centre of the mass
- results in a smaller impression
- crown will not seat properly
Double mix technique (steps) (5)
- Syringe wash material (injection type) around the prepared teeth
- Load the heavy body material into the tray
- Place the loaded tray in mouth
- Hold tray firmly until impression has set
- Remove impression from mouth, rinse and disinfect
Describe the putty wash technique
- Place putty into tray
- Cover putty with plastic sheet or mylar (to act as spacer)
- Place tray in mouth and seat
- After its set, remove impression
- Remove spacer from impression, rinse and dry the impression
- Impression now acts as very specific custom tray
- Syringe wash material around prepared area
- Syringe additional wash into the putty impression
- Seat and remove when set
Why must the gingival tissue be managed (2)
Haemostasis
Retraction
2 examples of haemostats
Aluminum chloride (Hemodent)
Ferric sulphate (Astrigident)
Features of Aluminum chloride
- Least irritating haemostatic agent used in cords
- Disrupts setting of PVS
- Rinsing thoroughly with water resolves this inhibitory effect
Features of ferric sulphate
- Does not traumatise tissue noticeably and healing is more rapid than AlCl3
- However, its quite acidic and can cause significant tissue irritation and post op root sensitivity
- Coagulates blood very quickly (application time is 1-3 min)
- Tissue stays displaced for 30 min
- Tissue is temporarily discoloured (yellow-brown) for 1-2 days
- Disrupts setting of PVS - must be rinsed before impressions
Why is retraction paste better than cord (4)
Easier to place (faster)
Less tissue trauma
More comfortable for pt
Hemostasis (AlCl3)
- Ex. 3M Astringent Retraction paste
