3. 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.
4. TYPE OF IMPRESSION TRAY
• 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.
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.
8. TYPES OF SPECIAL TRAYS
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
Tray with spacer & stop
• 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.
9. IDEAL REQUIREMENT FOR
SPECIAL TRAY
• 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.
10. MAKING THE SPECIAL TRAY
Step 1 – Identifying the peripheral extension
• An approximation of the peripheral extension may be made using the primary
model.
• Identify the deepest part of the sulcus, then draw the proposed periphery relative
to this.
• Draw the extent of the tray 2 mm toward the alveolar ridge from the deepest part
of the sulcus.
• 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.
11. Maxilla extension identification:
• Identify the junction between the hard and soft
palate (fovea palatinae) and use this landmark as
the periphery of the tray
• Ensuring that the entire tuberosities are included
• The distal extension of maxillary impression trays
should extend to the fovea palatine and extend
beyond the tuberosities to the hamular notches
12. Mandible extension identification:
• include the retromolar pad
• extend into the lingual sulcus such that the
periphery is just short of the mylohyoid ridge
• buccally to be just short of the external oblique
ridge
13. Step 2 – Prescription information
• The type of impression material that will be used for the
working impression.
• The type of tray required.
• The amount of spacer wax required.
• Any special features required (outline window tray
positions and whether a variable thickness of spacer wax
is required).
• Type of handle required (intraoral, extraoral, finger stops,
stepped or not and where the handle for a windowed
tray should be placed).
• The borders of the special tray should be marked using a
pencil.
14. Step 3 – Model preparation
• The cast should be soaked in slurry water.
• For close-fitting custom trays, any undercuts should be
filled with modeling wax. This ensures that the tray can be
removed from the model after casting without fracture of
the study model.
• The relief areas should also be marked in the cast. Some
areas are routinely relieved (e.g. incisive papilla, mid-
palatine raphe in the maxilla and lingual to the crest of
the ridge in the mandible).
• If the tray is to be spaced, adapt the appropriate thickness
of modeling wax to the model and trim short of the
required extension of the tray.
15. Step 4 – Adapting the Spacer
• The spacer should be about 1.5-2 mm thick.
• Spacers should be cut out in 2-4 places so that the special tray touches the ridge in these
areas.
• The part of the special tray that extends into the cut out of the spacer is called stopper.
–4 stoppers are placed
–two on the canine eminences on either side and two on the posterior parts of the ridge
–stabilize the tray during impression making
–The stopper can be a 2 mm square, a 2 by 4 mm rectangle over the crest of the ridge
16. Step 5 – Application of Separating Medium
• The separating medium is applied to avoid the special tray from binding to the cast.
• The spacer is removed carefully without any distortion.
• After applying the separating medium on the cast the spacer should be placed back on the
cast carefully.
• The spacer should also be coated with a separating medium.
• A surface tension reducing agent can be applied over the spacer to increase the wettability
of the separating medium.
• Commonly used separating media are Cold mould seal or Vaseline
17. Step 6 – Tray base construction
Using Light cure acrylic material
1. Adapt the light-curing blank to the model, or 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.
4. The curing process usually takes approximately 2 minutes; 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 and any
wax removed.
5. The final extension can be ground using a tungsten carbide bur and micromotor.
19. Using Cold cure Acrylic – Dough Technique
• The powder and liquid should be mixed in a mixing jar in the ratio of 3:1 by volume.
• If this ratio is not maintained and insufficient monomer is used will result in excessive shrinkage,
porosities and granularity may occur.
• After mixing the monomer & polymer the mix undergo 6 different stages:
1. Wet sandy stage, where the polymer is soaked in monomer.
2. Early stringy stage – where if the material is touched, fine filaments are seen sticking to the
finger.
3. Late stringy stage – where long strings are present. During the end of the late stringy stage
the manipulation should be started.
4. Dough stage – In this stage, the material is very workable.
5. Rubbery stage – where the material cannot be manipulated any more. Trying to manipulate
the material in this stage will result in excessive warpage of the tray.
6. Stiff stage – The material loses its elasticity and becomes more plastic. After the stiff stage,
the polymerization is almost complete.
20. Procedure
•Manipulation is done in the late stringy and the dough stages. The material is kneaded in the
hand, to achieve a homogenous mix.
•Then the material is shaped into a 2 mm thick sheet. Flattening the dough can be done using
a roller or a plaster mould or by pressing the material between two glass slabs.
•Separating medium should be applied over the roller or the glass slabs to avoid stickiness.
•The rolled sheet of acrylic is adapted over the cast from the center to the periphery. This
prevents the formation of wrinkles.
•Care should be taken not to apply excessive pressure on the ridge areas as it might lead to
the thinning of the tray.
•The excess material should be cut out with a wax knife
before the material sets.
•The set material is then trimmed to obtain a smooth
surface with smooth margins.
21. Step 7 – Handle construction
• Maxillary Tray Handle
The tray handle should be approximately 3-5mm wide in the area previously occupied by the
anterior teeth. The length from the highest point on the labial flange to the incisal edge is
approximately 22mm.
• Mandibular Tray handle
The handle is formed in a manner similar to that used for the maxillary handle. It should be
5-7mm wide in the molar area, tapering to 3 to 5mm wide anteriorly. Measuring from the
anterior arch of the tray, the height is 15-18mm. the handle will terminate 8-10mm from the
distal area of the final impression tray.
