CSAR 15 - Impressions for fixed prosthodontics Flashcards

1
Q

When taking an impression after crown preparation has taken place, what detail needs to be recorded?

A

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

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2
Q

When taking an impression after a crown prep, what 2 things need to be managed with the gingiva?

A

Moisture control

Deflection of the gingivae

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3
Q

How does moisture affect impression of a crown prep?

A

Impression material is hydrophobic

Stopping material flowing into sulcus and recording occlusal detail

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4
Q

Why is more LA sometimes given when taking an impression of a crown prep?

A

Acts as a vasoconstrictor

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5
Q

What does astringent do and how is it used? and give example.

A

Soak retraction cord in it - bigger bleed rub vigorously into area
Forms protein with blood to block vessels
Ferric sulphate, aluminium chloride

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6
Q

What is the % of ferric sulphate used?

A

15.5%

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7
Q

How are patients warned if ferric sulphate is given?

A

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

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8
Q

When taking an impression of a crown prep, how much does the sulcus need to be opened laterally? and why?

A

0.2-0.3mm by just removing the inner epithelium, less and the light body material will tear/deform

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9
Q

How can gingival deflection be done surgically? (avoid if poss)

A

Open sulcus by removing inner epithelium (0.3mm)
Use electrocautery, rotary curettage (bur without water) or laser
Unpredictable healing and potential recession

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10
Q

How can gingival deflection be done with retraction cords?

A

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

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11
Q

How is an impression taken for crown prep after retraction cord removed?

A

Air dry teeth
Light bodied silicone into open sulcus
Complete with heavy bodied silicone in tray

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12
Q

If patient loses temporary restoration for crown placement and gingival overgrowth occurs, what needs to be done?

A

Remove overgrown gingiva surgically

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13
Q

How is electrocautery carried out? What things do you need to be aware of?

A

Small brush movements
Don’t overheat bone = bony necrosis
Don’t touch tooth or amalgam
Use plastic mirror

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14
Q

How are silicone impressions stored on the way to the lab?

A

Unwrapped - they are dimensionally stable

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15
Q

If an impression has air blows and drags on the occlusal surfaces, what can this interfere with?

A

Prevents proper articulation

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