L6.Preliminary Impression

Question 0

Why is a custom tray necessary?

Answer 0

To accurately register moveable mucosa & create seal for retention

Question 1

Give 3 reasons for a preliminary impression

Answer 1

1. Treatment planning
2. Diagnosis
3. Make custom trays

Question 2

Alginates are what type of impression material?

Answer 2

Irreversible hydrocolloids

Question 3

When mixing alginates, is it water to powder or powder to water?

Answer 3

Powder to water

Question 4

The normal setting time for alginate is 1.5-5 min. How does temperature affect this?

Answer 4

Increased temperature leads to decreased setting time. Inverse relationship.

Question 5

Alginate requires bulk for accuracy and strength, thus when taking a preliminary impression, how much clearance must be given around all soft tissues?

Answer 5

5 mm. Alginate requires 3-5 mm thickness to maintain accuracy.

Question 6

How far posteriorly should maxillary and mandibular stock trays extend?

Answer 6

Maxillary: Slightly past the vibrating line
Mandibular: Cover retromolar pads

Question 7

The hamular notch is a palpatable depression located b/t what 2 structures?

Answer 7

The bony tuberosities anteriorly and the hamulus posteriorly.

Question 8

Why is it bad to seat the tray flat? What should be done instead?

Answer 8

Seating a tray flat is likely to trap air bubbles. It is better to seat either the posterior or anterior first, then seat the rest of the tray.

Question 9

When pouring the impression into stone, a two step process is used. What are the two steps? When is the second step initiated?

Answer 9

1. Pour stone into impression slowly to avoid air bubble entrapment. Allow initial set, until glossyness dissapears.
2. After the initial set flip model onto a stone base of uniform thickness. This base should exceed the outer impression by 4mm (=land area). Allow to set for ~30-45 min