Custom tray fabrication:

Question 1

What is a custom tray?

Answer 1

A special tray is a custom made device prepared for a particular patient which is used to carry, confine and control an impression material while making an impression.

Question 2

Why is it needed? What are its advantages?

Answer 2

• More accurate fit as it created specifically for that arch
• Provide anatomically correct extension of denture impressions
• Moreaccuratebordermolding
• Allow homogenous thickness of the
• impression material
• Less impression material is used
• Increased patient comfort
• Accuracy

Question 3

Materials used for
custom tray:

Answer 3

• Light-cured acrylic resin
• Chemically-cured acrylic resin fabrication
• Thermoplastic (Vacuumed)

Question 4

Types of custom trays:

Answer 4

• Spaced trays
• Close-fitting trays

Question 5

Spaced trays:

Answer 5

• Large undercut areas prohibit the use of close-fitting trays as removal from the mouth without causing distortion would be difficult and removal from the cast model would cause fracture of the cast.
• This type of custom tray can be used with alginate, elastomeric and impression plaster impression materials.
• The spacing between the tray and the tissues should be increased according to the depth of undercut, tear strength and elastic limit of the impression material.

Question 6

Close-fitting trays:

Answer 6

• Where the majority of the denture-bearing area is free from large undercuts, closefitting trays should be used.
• They allow pressure to be exerted on the denture-bearing area during the impression-taking procedure.
• Usually used with impression materials that are non elastic or rigid once set, typically zinc oxide eugenol paste.

Question 7

Window trays:

Answer 7

• There are occasions when a close-fitting custom tray would be desirable, but is contraindicated by the presence of a fibrous ridge.
• The problem can be overcome by the use of a close-fitting tray with a window cut in the tray around the fibrous ridge area.

Question 8

Ideal requirements:

Answer 8

• It should be well adapted to the primary cast.
• It should be dimensionally stable on the cast and in the mouth.
• The tissue surface should be free of voids or projections.
• It should be at least 2 mm thick in the palatal area and lingual flange for adequate rigidity.
• It should be rigid even in thin sections.
• It should not bind to the cast.
• It should be easy to remove.
• It should not react with the impression material.
• It should have a contrasting colour to make its margins appear prominent when placed in the patient’s mouth.
• It should have 2 mm relief near the sulcus so that green stick compound can be used to do border moulding.

Question 9

Stages of fabrication:

Answer 9

1. Identify and mark the anticipated denture extension on the cast
2. Mark the tray extension
3. 4. Apply separating media
4. Adding the spacer
5. Tray base construction
6. Handle construction
7. Light curing
8. Trimming the tray
9. Removal of baseplate wax

Question 10

Instruments and materials used for custom tray fabrication:

Answer 10

1. Cast of mandible and maxilla
2. Tray resin and monomer or light cure resin
3. Vaseline
4. Separating media
5. Red and blue pencil
6. Paper cup
7. Tongue blades
8. Slow speed handpiece
9. Acrylic bur
10. Wax spatula
11. Bunsen burner

Question 11

Step 1:

Identify and mark the anticipated denture extension on the cast.

What should be outlined on the cast?

Answer 11

Outlining

• Mark the depth of the vestibule with the first line
• Stay clear of the frenae

Question 12

Step 2:

Mark the tray extension.

Where should the tray be marked?

Answer 12

The tray periphery should be made slightly short of the required denture extension to allow room for the border molding and the impression material being used.

Question 13

Step 3:

Apply separating media.

Why?

Answer 13

Apply separating media so that the tray does not stick to the cast

Question 14

Step 4:

Adding the spacer.

What material is used?

Answer 14

Material: Baseplate wax

Question 15

Step 3:

Adding the spacer

What is its function?

Answer 15

1. The spacer allows the tray to be properly positioned in the mouth during border molding
2. It provides room the for the impression material
3. It minimizes the pressure that could distort the mucosa
4. It allows the impression to have an even thickness of impression material

Question 16

Step 4:

Adding spacer.

Which is the ideal thickness of a spacer?

Answer 16

The spacer should be about 1.5-3 mm thick.

Question 17

Step 4:

Adding spacer.

Adapting the spacer-How?

Answer 17

up until the second line drawn except in the posterior palatal seal

Question 18

The use of stops:

What is a stopper?

Answer 18

The part of the special tray that extends into the cut out of the spacer is called stopper.

Question 19

Spacer:

Where should the stops be cut?

Answer 19

Spacers should be cut out in 2-4 places so that the special tray touches the ridge in these areas.

• Ensures a uniform thickness of 2-3mm of impression material
• 4 stoppers are placed
• Maxilla: 2 on the canine eminences and 2 in the molar region
• Mandible: 2 in the incisal region and 2 in the molar region
• The stopper can be a 2 mm square over the crest of the ridge

Trim to “butterfly” ( to get the posterior palatal seal)

Stabilizes tray during impression taking

Question 20

5. Tray base construction:

What material should be used?

Answer 20

Light cured base plate material

Question 21

5. Tray base construction:

Steps:

Answer 21

1. Adapt the light-curing blank over the wax spacer, taking care to avoid thinning the material.
2. Trim the excess material with a wax knife to the required peripheral extension.
3. The material is cured by placing in an ultraviolet (UV) light box.

Question 22

6. Handle construction:

Which is the ideal Length, Width and thickness of a handle?

Answer 22

• Length: 15mm
• Width: 10mm
• Thickness: 3mm

Question 23

Handle design:

Which is the right angle for a maxillary and mandibular handle?

Answer 23

Lower tray: 90° angle

Upper tray: 45° angle

• The design is essential so that the tray does not interfere with lip movements during impression taking
• The handle must be long enough to allow easy manipulation of the tray during impression taking

Question 24

Light curing:

Answer 24

The curing process usually takes approximately 2-5 minutes(always check manufacturer’s instructions); however the light source may not cure the full depth of the material, particularly underneath the handle. Therefore it should be removed carefully and the curing cycle repeated with the tray inverted.