DMD 4
[Custom
Impression Trays for Fixed
Prosthodontics]
Cast preparation
1. Check all that necessary anatomy has been captured.
2. Check that all teeth are present without voids and intact.
3. Trim cast to the specified dimensions. (refer guide lines to pouring and trimming).
Cast should be 10-13 mm thickness at the thinness part (palate tongue space) trimmed with the occlusal plane
parallel to the bench. Do not cut out the tongue space. This weakens the cast and increases the risk of it
breaking, especially when articulating. Reduce tongue space to 10-13mm.
4. Trim cast symmetrically 3-4mm away from teeth following arch shape preserving the hamular notch, tuberosity
and retromolar pad.
Outline
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•
Draw the desired outline of the tray on to the cast.
The maxillary will be a horse shoe design extending a minimum of 5-6 mmm from the gingival margin covering
all the teeth.
Mandibular- extending 5-6mm pass the gingival margins.
•
•
Draw on location for v-shaped occlusal stops
•
Ideally four (4) V-shaped occlusal stops for tray stability, two in each quadrant and where possible a stop
should be placed anterior and distal to the tooth being prepared.
Otherwise three (3) V-shaped occlusal stops tripodised and widely spaced will also be acceptable.
•
•
In circumstances when three widely spaced occlusal stops cannot be achieved do the following;
•
•
The upper tray will require the palatal area to be covered with tray material for stability therefore do
not relief this area with wax.
While the lower tray with a mandible consisting of few teeth and edentulous ridge requires the
edentulous ridge to be covered with tray material for tray stability, but again do not relief this area with
wax
M.Jean-Louis
R Underdown
M.Jean-Louis
University of Sydney
7th March 2019
DMD 4
[Custom
Impression Trays for Fixed
Prosthodontics]
Wax Spacer
1. Using peripheral wax or softened baseplate wax block out any severe tissue or teeth undercuts.
2. Adapt a double layer (2mm thick) of baseplate wax 2-3 mm pass the pencil drawn outline (as you require
the finished product to be 5-6 mm pass the gingival margin).
3. Cut out the V-shaped grooves at desired location drawn on cast.
Tray Resin
1.
2.
3.
4.
5.
Place scrap tray resin into v-shaped groove area to slightly overfill cavity.
Adapt tray resin slightly pass the tray outline (5-6mm pass gingival margin).
Use excess/scrape tray resin and shape a handle 35mm long, 15-20mm wide and 5-6 mm thick.
Center and adapt / joint the resin. Tray handle should be placed at approximately 20straight out.
Lightly perforate un-cured tray resin with the back of a bur. Holes should be 10-12 mm apart and away from the
periphery.
6. Cure tray ensuring handle does not droop when placing in light curing machine.
Support the handle on the edge of the bowl.
SDH (6 sec+6 sec) remove immediately and cure for additional 6secs underneath to ensure stops and the handle
are cured.
Westmead- cure for 90 sec and additional 6 sec underneath.
M.Jean-Louis
R Underdown
M.Jean-Louis
University of Sydney
7th March 2019
DMD 4
[Custom
Impression Trays for Fixed
Prosthodontics]
Trimming
1.
2.
3.
4.
Check tray for stability. You can always use greenstick on the cast to improve stability.
Look at the desired outline drawn on the cast and trim back to line.
Smooth peripheries and check for any sharpness that may cause discomfort.
Using drill, you must perforate the predrilled holes entirely for the holes to be functional.
Clinic
Special trays are to be carefully assessed by the tutor on the primary cast before it is put into the patient’s mouth, so
that any additional modifications can be made. Further modifications may be required once placed in the mouth.
M.Jean-Louis
R Underdown
M.Jean-Louis
University of Sydney
7th March 2019