L7.Fabrication of Impression Trays & Record Bases

Question 0

A custom tray should be constructed to end how far short of the full vestibular depth when the tissues are at rest?

Answer 0

2-3mm

Question 1

What should the thickness of a custom impression tray be?

Answer 1

2-3mm

Question 2

Give at least 3 reasons why a custom tray is used?

Answer 2

1. Minimizes impression material distortion
2. Minimizes cost
3. Required to accurately reproduce moveable tissues
4. With border molding creates seal for retention

Question 3

When trimming custom trays to their correct extension into the vestibule (2-4 mm short of the vestibule depth), should you err on the side of under- or over-extension?

Answer 3

Under-extension. When border molding you may err on side of over-extension but with custom trays err on cutting them short

Question 4

Why is a spacer used when creating a custom tray?

Answer 4

A spacer (often way or tinfoil) along with undercut block-outs provide space for adequate bulk (thickness) of the alginate impression material (4-5mm)

Question 5

What type of material do we use to make custom trays in the lab? Why do we have to use Air Barrier Coating (ABC) during curing?

Answer 5

Tru-Tray Triad resin material is used to make custom trays. Triad resins have an outer air-inhibited layer that will not cure unless ABC is added

Question 6

How should the thickness of a record base compare to the thickness of a final denture?

Answer 6

They should be practically the same (borders and palate)

Question 7

How thick should the palate of the record base be?

Answer 7

1-2mm

Question 8

What is the only portion of a record base that shoul;d be polished?

Answer 8

Outside. Want slight roughness/don’t want to lose any detail on the interior

Question 9

Before adding pink triad denture base plate material for the record bases what 2 steps must be completed first?

Answer 9

1. Add blockout waxes

2. Add vaseline

Question 10

When adding the triad denture base material, what is the order in which it should be conformed to the cast? Why? Should the vestibules be filled?

Answer 10

First press down in the palate and then mold up and over the alveolar ridges into the vestibules to avoid trapping bubbles. The record base should completely fill the vestibule unlike the custom tray, which needed to be cut back 2-3mm from the depth of the vestibule.

Question 11

While you should avoid thinning the triad denture base material as much as possible, it is allowable to thin the material by 0.5mm over the residual rdges. Why?

Answer 11

To minimize record base reduction while setting teeth

Question 12

After the initial 2 min curing time on the master cast ABC should be applied. What is the next curing step?

Answer 12

Place record base with intaglio surface facing up and cure for an additional 6 min

Question 13

What change should be made to the hamular notch area following curing?

Answer 13

The hamular notch area should be thinned out to 1mm

Question 14

The borders of the record base should be the same thickness as the final denture flange. What is this thickness? What are two areas where the thickness is different (1 in maxillary 1 in mandibular)?

Answer 14

2-3mm
Max Exception = Palatal surface ~1-2mm
Mand Exception = Hamular notch & retromolar pad area ~1mm