CSAR 15 - Impressions for fixed prosthodontics Flashcards
When taking an impression after crown preparation has taken place, what detail needs to be recorded?
Tooth prep and 0.5mm below margin - giving emergence profile (therefore lab doesn’t make too bulbous and knows exactly where prep ends)
Occlusal detail of surrounding teeth
When taking an impression after a crown prep, what 2 things need to be managed with the gingiva?
Moisture control
Deflection of the gingivae
How does moisture affect impression of a crown prep?
Impression material is hydrophobic
Stopping material flowing into sulcus and recording occlusal detail
Why is more LA sometimes given when taking an impression of a crown prep?
Acts as a vasoconstrictor
What does astringent do and how is it used? and give example.
Soak retraction cord in it - bigger bleed rub vigorously into area
Forms protein with blood to block vessels
Ferric sulphate, aluminium chloride
What is the % of ferric sulphate used?
15.5%
How are patients warned if ferric sulphate is given?
Foul taste
Protein can be blue-black colour therefore can stain gingival tissues, should resolve in 1-2days, however aluminium chloride doesn’t stain the same
When taking an impression of a crown prep, how much does the sulcus need to be opened laterally? and why?
0.2-0.3mm by just removing the inner epithelium, less and the light body material will tear/deform
How can gingival deflection be done surgically? (avoid if poss)
Open sulcus by removing inner epithelium (0.3mm)
Use electrocautery, rotary curettage (bur without water) or laser
Unpredictable healing and potential recession
How can gingival deflection be done with retraction cords?
Gingiva is viscoelastic
For closed sulcus use 00 or 000 cord to compress and stop bleeding
Second cord to push tissues out using 0 or 1 (thicker gingiva 2/3/4), half into sulcus for maximal horizontal deflection
Cord packed for 6 minutes, after removal space closes below 0.2mm in 20-40 seconds, therefore work fast with impression
How is an impression taken for crown prep after retraction cord removed?
Air dry teeth
Light bodied silicone into open sulcus
Complete with heavy bodied silicone in tray
If patient loses temporary restoration for crown placement and gingival overgrowth occurs, what needs to be done?
Remove overgrown gingiva surgically
How is electrocautery carried out? What things do you need to be aware of?
Small brush movements
Don’t overheat bone = bony necrosis
Don’t touch tooth or amalgam
Use plastic mirror
How are silicone impressions stored on the way to the lab?
Unwrapped - they are dimensionally stable
If an impression has air blows and drags on the occlusal surfaces, what can this interfere with?
Prevents proper articulation
