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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.

3. Steps in the Casting Procedure Preparing the wax pattern for casting Spruing the wax pattern Attaching the sprue to the crucible former Investing the pattern in a casting ring Burnout of the wax pattern Casting Recovery Finishing and polishing

4. Preparing the Wax Pattern 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.

5. Spruing the Wax Pattern 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”

6. CONT… A sprue button 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.

7. The three basic requirements 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.

8. Materials Used to Make 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 .

9. Cont ….. 2 . Plastic Sprues: Solid Plastic: 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.

10. CONT.. 3. Metal Sprues : Non-rusting metals 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.

11. Sprue Diameter • It should 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.

12. 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.

13. Attaching the Sprue to 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.

14. Investing the Wax Pattern 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.

15. Casting Techniques The following step should be followed in any casting technique. Setting up the casting machine. Pre-heating the crucible. Weighing the alloy Casting the alloy

16. 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

17. Types of Soldering Soldering Techniques : Soldering for Metal Ceramic Restoration Oven Soldering Torch Soldering Infrared Soldering Laser Welding

18. 2: Soldering for 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 .

19. 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.

20. 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

21. 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.

22. 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.

23. 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.

24. Soldering technique Soldering Connector 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.

25. 2. Creating a Plaster 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.

26. 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