The document discusses impression trays, which are used to carry and control impression material in the mouth. It describes different types of trays, including stock trays, custom trays, and special trays. Special trays are custom-made for each patient based on a preliminary cast and are used to make final impressions. The document outlines the procedure for fabricating a special tray using materials like shellac, acrylic resin, and wax spacers. Special trays provide accurate impressions and are more comfortable for patients compared to stock trays.

1. SPECIAL TRAY
- BY SAZLANA RAHEEM
(4THYEAR)

2. Introduction
IMPRESSION TRAY
It is the device used to carry, confine & control the impression material
from the patient’s mouth.
During impression making, tray helps for insertion & removal of impression
material from the patients mouth.

3. Classification of impression tray
• Metallic trays
• Non metallic trays
• Stock trays
• Custom trays
• Edentulous trays
• Dentulous trays
According to
method of
fabrication of tray
According to
material used to
fabricate the
trays
According to teeth
present/absent in
mouth

4.  Stock tray:-
It is ready made & comes in specific sizes. So stock trays must
be selected for best fit.
They are re useable after sterilisation.
Custom tray:-
Or special tray are fabricated on the particular patient’s cast thereby
making it unique to the patient. This is why custom trays are always
better fit than stock trays.
They are useful only for the particular patient- then discarded.

5. Defination
 An individualised impression tray made from a cast recovered from
primary impression. (GPT8)
 It is used in making a final impression.
Primary
impressio
n
Preliminary
cast
Special
tray
Final
impressio
n

6. Advantages of special tray
1. Economy in impression material(used less impression material
required in special tray).
2. More accurate impression.
3. Special tray provides even thickness of impression material. This
minimise tissue displacement & dimensional changes of
impression materials.
4. The work with special tray is more easier & quicker than modified
stock tray to provide accurate impression
5. Special tray is more accurately adapted to the oral vestibules, this
helps in better retention of denture.
6. Special trays are less bulky than a stock tray which is more
comfortable for patient.

7. Materials used for construction of
special tray:-
Metallic
Cast metal
(Time
consuming)
(Not popularly
used)
Non
Metallic
ResinThermoplastic
material
1. Shellac base
plate
2. Impression
compound
1. Cold cure
acrylic resin
2. Hot cure
acrylic resin
3. Light cure
acrylic resin

8. Types of custom trays:-
1. Close fit tray
2. Tray with spacer & stop
Close fit tray:-
• As the name suggests, it is adapted directly on
the cast without any wax spacer.
• Usually used with impression materials that have a light
viscosity to obtain a wash impression eg: light bodies
elastomers, ZOE impression paste

9. Tray with spacer and stops:-
These trays use a wax spacer to provide space for the impression material. This is
because impression material used here need extra space as they have higher
viscosity eg: Alginate, medium & heavy bodied elastomers.

10. Fabrication of custom trays
Criteria for special tray construction

11. Procedural steps for custom tray with spacer & stop

12. A. Preparation of primary cast:
1. Undercuts should be find out with the help of surveyor &
should be blocked out.
2. Outline of border of the tray should be marked with
pencil which 2/3mm short of the reflection
3. The relief areas should also be marked in the cast.
4. The border of the tray marked on the cast may be
grooved deeper using the carver.

13. B. Adapting the relief wax:
 Relief wax should be adapted over the relief areas marked on cast
 Relief is given to prevent the tray from exerting excessive pressure on these
area during impression making. This also helps in recording the relief tissues
in a state of anatomical rest.
 In the maxillary cast, the relief wax should be adapted over the incissive
papilla & the mid palatine raphe. In the mandibular cast,the relief wax should
be adapted over the crest of the alveolar ridge.
 Materials for giving
relief:-
a) Baseplate wax
b)Non asbestos casting
liner.

14.  In addition to the relief wax, A spacer should be adapted throughout the
extent of special tray (coincide with the second line), except posterior palatal
seal area in maxilla and buccal shelf area in mandible.
C. Adapting the spacer:
 Function of spacer:-
a. The spacer allows the tray to be properly positioned in the mouth during
border moulding procedure
b. To allow the impression to have
an even thickness of impression
material.
c. Prevent distortion of the material
at final stage.

15. D. The use of stops:-
The spacer should be cut out in 2-4 places so that the special touches the
ridge in these areas.
Location: usually 4 stoppers are placed, 2 on the canine eminences on either
side & 2 on the posterior parts of the ridge.
Size & shape: stopper can be 2mmsquare
OR
2/4mm rectangle
Function of tissue stops:-
1. To orient the tray
2. For uniform thickness of the
3. impression material

16. E. Application of separating medium
• Apply separating media on the cast so that acrylic resin does not stick to
the cast.
• After applying the separating medium on the spacer
• Should be placed back on the cast carefully.
• Spacer should also be coated with a separating medium.
• Surface tension reducing agent can be applied over the spacer to
increase the wettability of the separating medium. Commonly used
separating medium are
Cold mould seal, tin foil , starch,Vaseline, cellulose, acetate etc

19. Shellac:-
 It was most commonly used material for preparation of special tray and
base plate.
 It is commercially available in separate shape for maxilla & mandible.
 Composition:-
Resin- 90.9%
Wax- 4%
Glutin- 2.8%
Moisture- 1.8%
Colouring agent- 0.5%

21. Techniques:-
 The cast should be coated with talcum powder or tin foil before the
adaptation of shellac so that it doesn’t stick to cast.
 All undercut should blocked out with wax.
 A spacer should be adapted. Use of modelling wax is avoided as a spacer
because it may melt during manipulation. Non asbestos casting liner is
used instead.
 The shellac plate should be positioned on the cast
& the brush flame of the Bunsen burner should be moved across
. the plate till it becomes shiny & begins to sag.
 In maxillary cast, palatal surface is adapted & for mandibular cast lingual
flange is adapted first by using wet cotton or finger.

22.  After adaptation of them plate should be reheated & adapted over the crest of
residual alveolar ridge. This prevents the appearance of wrinkles.
 After completing adaptation, the material should be cut
using a scissor leaving about 5mm excess material in the
border.
 The shellac should be re adapted over the entire cast,especially the sulcus area
 Excess material should be carefully cut at the deepest point of the sulcus using a
scissor.

23.  The margin of the special tray should be finished &
Smoothened using triangular file.
 Filing should be done carefully till the margins of
the special tray become 1-2mm deficient of sulcus.
 Striations should be made on the anterior portion of the
tray over the incisive papilla using hot wax knife. This is
done to Increase the mechanical retention of the handle.
 A small rectangular strip of shellac should be heated over the flame and rolled to
form a cylinder.
 One end of the cylinder should be heated so that the material start to sag.

24. The sagging end of the cylinder should be compressed
firmly over the striation made on the tray near the incisive
papilla. The handle should be completely fused to tray.
 A hot wax knife can be used to fuse & smoothen the junction of the handle and the
tray
 The special tray & it’s handle should be sand papered
for a perfect smooth finish. The handle should be 3-4mm
wide 8mm long & 8mm high.
 Overheating may lead to melting & flowing of
Shellac into the pores of the cast.
 Over heating the special will also produce smoke, bubble, blackening & leaching of
shellac & wax.
 These trays should be fabricated 6 hours prior to impression procedure.

25. Cold cure acrylic tray
material:-
 It is also known as auto polymerised resin.
Technique-
First, the relief area & the borders of the
Special tray are marked. A wax spacer is
adapted on the relief area.Separating medium
Is coated on the entire cast & over the spacer
2 major technique are used in fabrication of
An acrylic special tray:-
1) Sprinkle on technique
2) Dough technique

26. Sprinkle on technique:–
 The powder & liquid are loaded in separate dispensers.
 A small quantity of powder is sprinkled on a particular
area over the cast & liquid is sprinkled over the powder.
 Sprinkling drops of the liquid polymerises the powder. This is continued till the
entire ridge & the associated landmarks are covered.
Dough technique:–
The powder & liquid should be mixed in the mixing jar in the ratio of 3:1 by volume. If
this ratio is not maintained & insufficient monomer is used, excessive shrinkage,
porosities & granularity may occur.
After mixing the monomer & polymer the mix undergo 6 different stages:
Wet sandy stage, early stringy stage, late stringy stage, dough stage, rubbery
stage, & the stiff stage.

27.  Procedure:-
 Manipulation is done in the late stringy and dough stages. The material is needed
in the hand, to achieve homogeneous mix.
 Then material is shaped into 2mm thick sheet. Flattening the dough can be done
using roller or a plaster mould or by pressing the material between 2 glass slabs
 Separating medium should be applied over
the roller or glass slabs to avoid stickiness.
 The rolled sheet of acrylic is adapted over the cast from the centre
to the periphery. This prevents the formation of the wrinkles.
 The excess material should be cut out with the
B.P blade before the material sets.
 The set material is then trimmed to obtain a smooth
surface with smooth margin

28. Fabrication of Handle:-
 Criteria of handle:-
1) The handle should be parallel to the long axis of the teeth that are also replaced.
2) The handle should not arise horizontally from the tray because it may interfere
with lip movement.
3) It should be 3-4mm thick, 8mm long & 8mm high.
4) The vertical distance from sulcus to the handle is 2cm
5) The handle upstand must be made long enough for the
handle to exit through the oral cavity
6) For mandibular tray 2 posterior handle should be given
as finger rest

29. Function of handle:-
1. Support the lip while making impression
2. Tray handles are particularly helpful
when loading, placing & orientating
custom tray in the mouth.
Functions of finger rest:-
1. Stabilise tray in mouth.
2. Equal distribution of pressure.
3. Reduces pressure applied to tissues.