Special tray prosthodontics

complete denture, Special tray, prosthodontics slides, ppt
to know complete about special tray

1. SPECIAL TRAY - by Sazlana Raheem ( 4 th year )

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 impression Preliminary cast Special tray Final impression

6. Advantages of special tray Economy in impression material(used less impression material required in special tray). More accurate impression. Special tray provides even thickness of impression material. This minimise tissue displacement & dimensional changes of impression materials. The work with special tray is more easier & quicker than modified stock tray to provide accurate impression Special tray is more accurately adapted to the oral vestibules, this helps in better retention of denture. 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 Resin Thermoplastic material Shellac base plate Impression compound Cold cure acrylic resin Hot cure acrylic resin Light cure acrylic resin

8. Types of custom trays:- Close fit tray 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. Preparation of primary cast: Undercuts should be find out with the help of surveyor & should be blocked out. Outline of border of the tray should be marked with pencil which 2/3mm short of the reflection The relief areas should also be marked in the cast. 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:- 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:- To orient the tray For uniform thickness of the 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

17. 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%

18. 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.

19. 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.

20. 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.

21. 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.

22. 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

23. 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.

24. 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

25. 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

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