Special Tray: a device that is used to carry, confine and control impression material while making a final impression.
Fabrication: a. Tray outline To make a tray outline, one must know how to interpret the anatomic land marks on the primary cast obtained from preliminary impression.
* With an indelible pencil, draw a line transversely across the posterior border connecting the two hamular notches, 2 mm distal to fovea palatine. * Draw a line outlining the muco-buccal fold at the point where the buccal reflection leaves the lateral wall of the alveolar ridge.
Maxillary Cast
Mandibular cast
b. Methods
Autopolymerizing resin impression trays.
a. Sprinkle on methods
b. Finger adapted dough method
2. Vacuum-adapted method
*After making the tray outline and block the undercuts, place the relief on the cast, such as a wet sheet of non asbestos casting ring lining material, that will not melt during heating of the thermoplastic resin sheet. *Center the cast on the vacuum adapted plate and a sheet of appropriate size thickness in the heating frame, rotate the heating unit into position and continue heating until the specified sag in the material occurs. *Lower the frame and resin sheet onto the cast and start vacuum adaptation. Once adaptation is completed, allow it to cool and then remove the cast from the unit. Remove the tray from the cast and trim the borders. *Add handles from cold cure resin or from pre formed metal handles and store the tray on cast until needed.
3. Shellac Method
Tray Handle
Evaluation and correction
The maxillary special tray
The mandibular special tray
