Why is a custom tray necessary?
To accurately register moveable mucosa & create seal for retention
Give 3 reasons for a preliminary impression
- Treatment planning
- Diagnosis
- Make custom trays
Alginates are what type of impression material?
Irreversible hydrocolloids
When mixing alginates, is it water to powder or powder to water?
Powder to water
The normal setting time for alginate is 1.5-5 min. How does temperature affect this?
Increased temperature leads to decreased setting time. Inverse relationship.
Alginate requires bulk for accuracy and strength, thus when taking a preliminary impression, how much clearance must be given around all soft tissues?
5 mm. Alginate requires 3-5 mm thickness to maintain accuracy.
How far posteriorly should maxillary and mandibular stock trays extend?
Maxillary: Slightly past the vibrating line
Mandibular: Cover retromolar pads
The hamular notch is a palpatable depression located b/t what 2 structures?
The bony tuberosities anteriorly and the hamulus posteriorly.
Why is it bad to seat the tray flat? What should be done instead?
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.
When pouring the impression into stone, a two step process is used. What are the two steps? When is the second step initiated?
- Pour stone into impression slowly to avoid air bubble entrapment. Allow initial set, until glossyness dissapears.
- 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
