Department of Prosthodontics Dr Ramya Srlecturer Impression Trays DR G PHANI KRISHNA DEFINITION A receptacle into which suitable impression material is placed to make a negative likeness ID: 1046771
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1. Impression TraysSIBAR INSTITUTE OF DENTAL SCIENCESDepartment of ProsthodonticsDr. Ramya. Sr.lecturer
2. Impression TraysDR. G. PHANI KRISHNA
3. DEFINITIONA receptacle into which suitable impression material is placed to make a negative likeness; orA device that is used to carry, confine and control impression material while making an impression.
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5. PARTS OF IMPRESSION TRAYBodyFlangeHandel
6. REQUIREMENTS OF IMPRESSION TRAY1. The tray should be rigid and strong but not too thick. 2. The tray should simulate the finished denture in size and shape. 3. The border extension of the tray should be 2mm short of the vestibular depth with no interference with muscle or frenal attachment. 4. The entire borders of the tray should be smooth and rounded. 5. The tray should retain its shape throughout the impression procedure and pouring of impression. 6. The handle of the tray should be angulated.
7. CLASSIFICATION OF IMPRESSION TRAYSImpression trays are of two types:1. Stock tray or Pre-fabricated tray2. Special tray or Custom tray
8. Types of Impression trays:Maxillary / MandibularDentulous / EdentulousVarious sizes: 1, 2, 3, 4Various materials: Metal or Plastic or Acrylic
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10. STOCK TRAY OR PRE-FABRICATED TRAYFit to many patientsApproximate shape of the arche – various sizes – Maxilla/ MandibleUsed for Diagnostic or Primary impressions.
11. TYPES OF STOCK TRAY: (Dentulous or edentulous)PerforatedNon perforatedRim-lock traySegmental trays
12. ADVANATGESRigid and support the set impression material. Dimensionally stable Tray is smooth, so injury to oral tissues is avoided. Multiple set in several patients.
13. DISADVANTAGESDimensionally accurate impression is difficult to make with stock tray Uniform space is not available for impression material. Flanges of stock trays may be over extended or under extended
14. SPECIAL TRAYFits only for a specific patientUsed for secondary of final impression
15. TYPES OF SPECIAL TRAYTray with spacerTray without spacer/ Close fit
16. MATERIALS USED FOR FABRICATION OF SPECIAL TRAYTray compound Tray acrylic Shellac Vacuum formed thermoplastic resin sheet Wax Old denture
17. ADVANTAGESDimensionally accurate impression can be made Uniform space available for impression materialsOver and under extension of tray flanges can be avoided Non stress bearing area can be relived with the use of spacer
18. DISADVANTAGESCan be used only for individual patient. Fabrication of custom trays is time consuming based on the material selected Rigidity is less when compared to metallic stock tray. Dimensional stability is less when compared to metallic stock tray
19. SPECIAL TRAY/ CUSTOM TRAY/ INDIVIDUALIZED TRAY
20. DEFINITIONAn individualized impression tray made from a cast recovered from a preliminary impression; it is used in making a final impression.
21. STEPS IN THE FABRICATION OF SPECIAL TRAY:OutlineBlock out and reliefWax spacer adaptation
22. STEPS IN THE FABRICATION OF SPECIAL TRAYOUTLINE: Extensions of the tray is outlined in the diagnostic cast, 2mm short of the vestibular depth to provide space for border moulding material.
23. 2 BLOCK OUT AND RELIEF: Block out is done in those areas which prevent placement and removal of the custom tray. Wax relief is placed over tissues that are easily displaced and relief areas in the maxilla and mandible.
24. 3 WAX SPACER ADAPTATION: Wax spacer which 4mm short of the vestibular depth is adapted on the diagnostic cast before the adaptation of special tray material.
25. SPACERUse of spacer: Provides space for the secondary impression material in the special tray. Provides relief for the easily displaced tissues and relief areas.
26. Spacer DesignsBased on the type of impression technique and type of impression material used, the design of the spacer varies.Based on the impression technique:Mucocompressive technique – No wax spacer is usedMucostatic technique: Full wax spacer is usedSelective pressure technique: Maxilla: Full wax spacer with cut back in PPS, umbrella shaped, ‘I’ shaped and ‘T’ shaped spacers are used.Mandible: Full wax spacer with cut back in Buccal shelf Area.
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28. OCCLUSAL STOPS OR TISSUE STOPSThey are made by removing 4mm square or 2x4mm rectangle blocks of wax to expose the cast on the ridge region.Location: Located at canine and 1st molar teeth region as they have more periodontal surface area for wider distribution of forces.Purpose of occlusal stops: Prevent the tray from coming into intimate contact with the tissues.Helps in proper orientation of the tray.Helps in equal distribution of pressure
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