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FDP presdyr5c75f7676fg86giuviu8entation.pptx
- 1. GROUP 2 LAB PROCUDURE SPECIFICALLY •CAST • SOLDERING NAMES OF GROUP • Muniira abdirahman • Khadra abdijalil • Abdirahman muse • Abdirahman saleban • Ahmed abdihakim • Abdiqadir omer
- 2. Introduction to Casting •Definition: Casting is a manufacturing process where a liquid material is poured into a mold to solidify and take the mold's shape. • Lost Wax Casting Technique: Introduced by Taggart in 1907 • Most preferred casting technique, especially in dentistry. • Applications: Dental restorations (crowns, bridges, etc.). • Precision parts in engineering and jewelry.
- 4. Steps in theCasting Procedure 1. Preparing the wax pattern for casting 2. Spruing the wax pattern 3. Attaching the sprue to the crucible former 4. Investing the pattern in a casting ring 5. Burnout of the wax pattern 6. Casting 7. Recovery 8. Finishing and polishing
- 5. Preparing the WaxPattern for Casting After fabricating the wax pattern, the following procedures should be carried out prior to casting • The margins of the wax pattern should be readapted. • The pattern is checked for smoothness, finish, and contour. • The sprue should be attached to the thickest portion of the wax pattern. • The wax patterns can be removed from the die using the sprue. • A surfactant should be applied on the wax to obtain better wetting of the investment. • The wax pattern is invested immediately to prevent distortion.
- 6. Spruing the WaxPattern • The wax pattern should be sprued before investing. • This sprue acts as a channel for metal flow during casting. • Sprue Formers and Sprues • A sprue is defined as, “The channel or hole through which plastic or metal is poured or cast into a gate or reservoir and then into a mold”. “The cast metal or plastic that connects a casting to the residual sprue button”
- 8. CONT… • A spruebutton is defined as, “The material remaining in the reservoir of the mold after a dental casting • A sprue former or sprue pin is defined as, • “ A wax, plastic, or metal pattern used to form the channel or channels allowing molten metal to flow into a mold to make a casting” • Sprue Design • Sprue design will vary depending on the type of restoration being cast, the alloy used and the casting machine.
- 9. The three basicrequirements of a sprue design are: • The sprue must allow the molten wax to escape from the mold. • It must enable the molten metal to flow into the mold with minimal turbulence. • The metal within the sprue must remain molten slightly longer than the alloy that has filled the mold. This will act as a reservoir to compensate for the shrinkage that occurs during solidification of the casting.
- 10. Materials Used toMake Sprues 1. Wax Sprues: • Preferred for most castings because they melt at the same rate as the pattern. Allow easy escape of molten wax during burnout.
- 11. Cont….. 2. Plastic Sprues: SolidPlastic: Soften at higher temperatures and may block wax escape, causing rough castings. Hollow Plastic: Permit wax escape during burnout, but are more rigid and resist distortion.
- 12. CONT.. 3. Metal Sprues: Non-rustingmetals prevent contamination of the wax. Hollow metal sprues provide more contact surface and strengthen the attachment. Usually removed before casting; careful removal is necessary to avoid contamination in the mold.
- 13. Sprue Diameter • Itshould be larger than the thickest portion of the pattern. • Reservoir should be provided to prevent localised shrinkage porosity. Recommended Sprue Diameters Molar Metal-Ceramic Restorations: Use 2.5 mm (10 gauge) sprues for molar restorations to ensure proper metal flow. Premolar Partial Veneer Restorations: Use 2.0 mm (12 gauge) sprues for premolar restorations for smooth casting. Centrifugal Casting: Narrow sprues are sufficient for centrifugal casting machines, where air pressure inside the sprue prevents premature metal flow until the centrifugal force is released.
- 14. Positioning the Sprue: Angle of Placement Place the sprue at a 45° angle near the bulk of the pattern for smooth metal flow. The axial walls should form a 135° obtuse angle with the sprue to prevent air entrapment and suck-back porosities. Flared Attachment: The point where the sprue attaches should be flared to reduce turbulence during metal flow.
- 15. Attaching the Sprueto the Crucible Former Crucible Former: The sprue is attached to a crucible former, a conical structure that helps guide the molten metal during casting. Ensure the sprue’s terminal end is about 6 mm from the free end of the investment to allow air escape. Venting: Small auxiliary venting sprues should be added to improve casting quality by allowing gases to escape.
- 16. Investing the WaxPattern Casting Ring & Investment: The wax pattern is placed in a casting ring and covered with investment material based on the alloy type (gypsum for high noble alloys, phosphate for base metals). Surface Tension Reduction: A surfactant is used on the wax pattern to improve wetting of the investment. Ring Liner: Cellulose or other liners are used to ensure uniform expansion of the mold. Bench Setting: After investing, allow the mold to bench set for at least one hour before further processing.
- 17. Casting Techniques • Thefollowing step should be followed in any casting technique. 1. Setting up the casting machine. 2. Pre-heating the crucible. 3. Weighing the alloy 4. Casting the alloy
- 18. Soldering • Flux Definition: •Soldering flux is a chemical agent that enhances the flow of soldering metal during the soldering process. • Etymology: • The term "flux" is derived from Latin, meaning "flow.“ • Antifluxes: • Chemicals that limit the flow of metals are known as antifluxes. • Functions of Flux: • Protector: Covers metal surfaces to prevent oxide formation. • Reducer: Aids in reducing existing oxides on the metal surface. • Solvent: Dissolves and removes any present oxides
- 20. Types of Soldering SolderingTechniques: • Soldering for Metal Ceramic Restoration • Oven Soldering • Torch Soldering • Infrared Soldering • Laser Welding
- 21. • 2: Solderingfor Metal Ceramic Restoration • Pre-Ceramic Soldering: • Conducted before ceramic application (1075-1120°C). • Allows for framework adjustments. • Post-Ceramic Soldering: • Done after ceramic firing (920°C). • Requires caution to avoid ceramic staining.
- 22. • Advantages: • Pre-Ceramic:Easier adjustments and patching. • Post-Ceramic: Better access for porcelain build-up. • Disadvantages: • Pre-Ceramic: Difficult to build ceramic on already soldered units. • Post-Ceramic: Risk of sagging and requires re-glazing.
- 23. 3: Oven Soldering •Oven Soldering Process: • Performed in a vacuum or air. • Involves placing solder in the joint space and heating in a furnace. • Advantages: • Produces superior joint strength. • Disadvantages • The parent metal will sag or melt if heatedfor a long time
- 24. 4. Torch Soldering •Process: • Conducted under direct flame using a gas air torch. • The torch flame consists of two parts: • Reducing Part: Higher temperature. • Soft Brush Part: Used to melt the solder. • Technique: • The flame should be swiped over the solder for 4 to 5 minutes. • Avoid holding the flame in a stationary position to ensure even heating.
- 25. 5. Infrared Soldering: •Suitable for low-fusing connectors. • Offers good accuracy with controlled heating. • Joints exhibit similar strengths to conventional soldering. • Protective eyewear is required for operators.
- 26. 6. Laser Welding •Used to join titanium components in dental crowns, bridges, and partial dentures. • Utilizes pulsed high-power Neodymium lasers with low thermal influence. • Allows for handheld parts due to minimal heat generation. • Maximum penetration depth of laser welding is 2.5 mm, providing superior joint strength.
- 27. Soldering technique 1. SolderingConnector i. Design Wax Pattern Fabrication: Design of the connector is determined during wax pattern fabrication. Requires a uniform space of 0.25 mm between parent components for soldering. II. Component Insertion: Smaller units are inserted separately into the patient's mouth.
- 28. 2. Creating aPlaster Index I. Plaster Index Formation: • A thick mix of quick-setting plaster is molded over the inserted units. • Once set, the plaster is removed along with the components. II. Inversion and Wax Placement: • Inverted plaster index reveals the tissue surface of components. • A triangular piece of utility wax is placed to shape the soldering assembly.
- 29. Soldering Process Steps I.Investment and Wax Elimination: • The units are invested, and the wax is eliminated using boiling water or chloroform. • Coating and Preheating: • The restoration area surrounding the joint is coated with anti-flux. • The assembly is preheated in a burnout furnace before soldering. • Soldering Execution: • Connectors are soldered using a torch or furnace. • Disadvantage: • Not an economical method for all cases