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Semelhante a Casting Procedures in Dentistry
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Casting Procedures in Dentistry
- 1. Laboratory Procedures for Removable Partial Dentures Mustafa Batoor Final Year BDS Roll No.: 29
- 2. Objectives At the end of the presentation we should be able to: 1. Describe all laboratory steps in making a RPD. 2. Differentiate the types of block- out.
- 3. Why do we need to know the lab procedures??? Knowledge of the laboratory phase of partial denture construction is essential for the clinician, who must assume total responsibility for the design and the quality control of all aspects of its construction.
- 4. Steps in making a RPD 1. TOOTH PREPARATION / CAVITY PREPARATION 2. IMPRESSION 3. CAST DUPLICATION 4. WAX PATTERN FABRICATION 5. SPRUING 6. INVESTING 7. BURNOUT 8. CASTING 9. DIVESTING 10.CLEANING & POLISHING
- 5. Step 1: Tooth Preparation
- 7. Step 3: Duplicating a Stone Cast A stone cast may be duplicated for many reasons: i. Preservation of original casts ii. Processing of interim prosthesis iii. To check the fit of the framework
- 8. iv. A stone cast may also be duplicated with block-out of wax for: Formation of investment (refractory) cast for framework fabrication
- 9. Duplication Materials & Flasks Duplicating materials are: 1. Colloidal (agar) 2. Silicone
- 10. • Colloidal materials are made fluid by heating and return to gel while cooling.
- 11. Duplicating Procedure A) Blockout on the master cast with wax.
- 12. Types of Block Out Four types of block out are there: • Paralleled Blockout • Shaped Blockout • Arbitrary Blockout • Relief
- 13. Paralleled Blockout Proximal tooth surfaces to be used as guiding planes and below height of contour.
- 14. Shaped Blockout On buccal and lingual surfaces to locate wax patterns for clasp arms.
- 15. Arbitrary Blockout Labial surfaces and labial undercuts not involved in RPD design.
- 16. Relief • In the edentulous areas • Beneath lingual bar connectors • Areas in contact with thin tissues
- 17. B) Attach cast to the bottom of the flask so that it does not move
- 22. Making Refractory Cast (Investment Cast) – withstands high temperature
- 23. Step 4: Waxing the RPD Framework Preformed wax patterns
- 24. Design Transfer: Before the actual waxing can begin, the design must be transferred on the refractory cast.
- 26. Wrought wire: can be made at the time of wax patterns or soldered to the framework
- 27. Step 5: Spruing
- 28. Sprues (ingates) have the purpose of leading the molten metal from the crucible into the mold cavity. *
- 30. Step 6: Investing the Sprued Pattern
- 31. The investment for a removable partial denture casting consists of two parts: 1. the investment cast on which the pattern is formed
- 32. 2. The outer investment surrounding the cast and pattern. The outer investment is confined within a silicone ring or metal ring.
- 33. If the silicone ring is removed before the casting is done and is called ringless casting technique.
- 34. If the metallic ring is used, it is not removed.
- 35. Cross sectional view of waxing, investing and sprue:
- 36. Step 7: Burnout
- 37. The burnout procedure serves three purposes: i. Drives off the moisture in the mould ii. Vaporizes and thus eliminates the pattern, leaving a cavity in the mold iii. Expands the mold to compensate for contraction of the metal on cooling.
- 38. Step 8: Casting
- 39. Why is the casting needed?? To make dental restorations such as inlays, onlays, crowns, bridges and removable partial dentures.
- 40. Objectives of Casting 1) To heat the alloy as quickly as possible to a completely molten condition.
- 41. 2) To prevent oxidation by heating the metal with a well adjusted torch.
- 42. 3) To produce a casting with sharp details by having adequate pressure to the well melted metal to force into the mold.
- 44. The metal is melted and the molten alloy is forced into the mold cavity by centrifugal force.
- 45. Faults in Casting Finning and bubbling Incomplete casting Porosity in casting Oversized or undersized casting
- 46. Step 9: Divesting (Removing the cast from the investment)
- 47. Once the alloy cools it is divested and the remaining investment material is sandblasted using aluminum oxide.
- 48. Step 10: Finishing and Polishing
- 49. Thank You!
- 50. References McCracken's Removable Partial Prosthodontics – 11th Edition www.odlinc.org www.intranet.tdmu.edu.ua cyberspaceandtime.com
Notas do Editor
- Abutment contour should be altered during mouth preparations in the following sequence. Proximal surface is prepared parallel to path of insertion to create guiding plane Height of contour on buccal (and lingual) is lowered when necessary to permit clasp placement to be located more favorably (i.e., middle-gingival 3rd). Tooth reduction should be parallel to the guide plane reduction, followed by contouring the tooth occlusal to the new height of contour to allow a gradual convergence. Labial reduction demonstrating favorable location of height of contour and mesio-buccal undercut location. Occlusal convergence of height of contour is also evident. Spoon-shaped disto-occlusal rest preparation that will direct occlusal forces along long axis of tooth should be the final step in mouth preparation.
- A stone cast maybe duplicated
- Sprue: Part of casting that acts as a channel for the molten metal to flow into the mold cavity after the wax has been eliminated.
- A) Blockout on the master cast with Ney blockout wax (can withstand high temperature)
- Paralleled Blockout: Proximal tooth surfaces to be used as guiding planes and below height of contour.
- On buccal and lingual surfaces to locate wax patterns for clasp arms.
- Arbitrary Blockout: Labial surfaces and labial undercuts not involved in RPD design.
- Relief wax is placed in the edentulous areas Beneath lingual bar connectors Areas in contact with thin tissues
- Preformed plastic wax patterns are available which are made from soft plastic material which tend to stretch on removal from their backing.
- Before the actual waxing can begin, the design must once again be transferred on the refractory cast (beading the master cast helps in this procedure).
- Sprue: Part of casting that acts as a channel for the molten metal to flow into the mold cavity after the wax has been eliminated.
- * Diagrammatic representation of a dental casting mold Properties of Sprues: they should be large enough to accommodate the entering molten metal and of the proper shape to lead the metal into the mold cavity quickly. Should provide a reservoir of molten metal from which the casting may draw during solidification, thus preventing porosity caused by shrinkage.
- Investment Materials: Gypsum Bonded Materials: Silica + Calcium Sulphate Hemihydrate Silica Bonded Materials: powdered quartz/cristobalite + silica gel Phosphate Bonded Materials: Silica powder + Magnesium Oxide + Ammunium phosphate
- The investments used for RPD casting is ethyl silicate bonded investments and the alloys mainly used are chromium- cobalt or titanium.
- DEFINITION:“Casting is the process by which a wax pattern of a prosthesis is fabricated and converted to its metallic replica”
- Finning: occurs when the investment is heated up too fast. Incomplete casting: due to lack of alloy, narrow sprue, improper angulation … Porosity: due to particles that attach to the sprue or fall in the molten metal, gaseous porosity due to gases which become dissolved… Oversized or undersized, due to shrinkage, or improper consturaction…
- Gross finishing is accomplished with abrasive stones or sintered diamonds (except at contact areas) Polishing; framework finished with a rubber polishing point prior to final “high-shine” polish. The following rules for finishing are important: High speeds are preferable to low speeds. The wheels or points and the speed of their rotation should do the cutting. A definite sequence for finishing should be adopted and followed for every framework. Clean polishing wheels should be used. Each finishing operation should completely remove all scratches left by the preceding one.