impression trays definition and classification

1. Impression trays
Definition and classification

2. Impression tray
• It is a device used to carry ,confine & control impression material
while making an impression

3. Objectives
• Impression try must be rigid because Flexible trays cause
distortion of impression
• It should be dimensionally stable
• It should provide uniform space for impression material.
• It should be smooth to avoid injury to oral structure
• It should not distort the tissue in the vestibular areas
• It should support set impression materials when removed
from mouth so that a cast can poured

4. Parts of the tray
handle
flanges
floor
1- Body: which consist of : a) floor. b) flanges.
2- Handel.

5. • There are upper tray to make impression of upper arch & lower tray
to make impression of lower arch.
• The difference between them is that in the upper tray, there is the
palatal portion we called (vault) & in the lower tray there is the
lingual flanges.
• The handle is an extension from the union of the floor & labial
flange in the middle region (midline), it's (L) in shape so that it will
not interfere with lip during impression procedure.

6. Classification of trays
Based on whether they are prefabricated or individualized
• 1- prefabricated Stock tray: used for primary impression procedure.
• Perforated trays
• Non perforated trays
• Rim lock trays
• 2- individualized Special tray/ custom try which is used for final
impression procedure.
• Close fitting special try
• Loss fitting or spacer special try

7. • Based on shape of stock trays:
• 1- Stock tray for dentulous patient (Square).
• 2- Stock tray for edentulous patient (oval).
• We can distinguish between them by: stock trays for dentulous
patient have long flanges, wide and flat floor, while the other
have short flanges, oval and narrow floor.
• 3-Tray with combination flat and oval floor are suitable for
partial denture work.

8. Based on material used for fabrication
• a) metallic.
• b) Non- metallic.
Material used for fabrication stock Tray
1- metal
Tin-lead alloy
Stainless steel
2- plastic

9. • Material used for fabrication of custom tray
• Tray compound
• Tray acrylic
• Shellac
• Vacuum formed thermoplastic resin sheet
• Wax
• Old denture

10. advantages
I-stock tray
1-Rigid and support the set impression material.
2- Dimensionally stable
3- Tray is smooth, so injury to oral tissues is avoided.
4- Multiple set in several patients.
II- Custom trays
1- Dimensionally accurate impression can be made
2- Uniform space available for impression materials
3- Over and under extension of tray flanges can be avoided
4- Non stress bearing area can be relived with the use of spacer

11. advantages
III- Tray acrylic special tray
1- easy to fabricate.
2- require no special equipment.
3- sufficient dimensional stable
4- can be made thin but reasonably rigid.
5- modified easily, by grinding with acrylic bur.
IV- Shellac special trays:
Impression tray can be fabricated very rapidly using thermoplastic
shellac plate.
V-Thermoplastic resin special trays:
Very minimal amount of time is used in constructing the tray.

12. disadvantages
I- Stock trays:
1- dimensionally accurate impression is difficult to make with stock
tray
2- uniform space is not available for impression material.
3- flanges of stock trays may be over extended or under extended
II- Custom trays:
1- can be used only for individual patient.
2- fabrication of custom trays is time consuming based on the
material selected
3- Rigidity is less when compared to metallic stock tray.
4- Dimensional stability is less when compared to metallic stock
tray

13. disadvantages
III- Tray acrylic special trays
Dimensional stability is less due to polymerization s
shrinkage.
IV- Shellac special trays:
1- lack of dimensional stability, especially during application of
heat when border moulding the tray with impression compound.
2- Brittle material, so chances of breakage while impression
making and fabrication of cast.
V- Thermoplastic resin special trays:
1- specialized equipment requirement required.
2- Expensive due to the requirement of costly equipment

14. Factors effect in selection of tray
I- based on the type of impression
1- Diagnostic impression = stock trays.
2- Primary impression= stock tray
3- Secondary impression= custom trays
II- Based on complete or partial absence of teeth:
1- Edentulous impression = non perforated trays
2- dentulous impression
• Perforated trays
• Non perforated trays with special adhesive.
III- Based on impression material used:
1- Alginate= perforated trays
2- Impression compound= non perforated trays.