Soldering in Partial Denture Notes

Soldering in Partial Denture

Soldering Definition: It is the joining of metals by use of a filler metal, which has a lower fusion temperature than that of the metal parts being joined.

Soldering Types in Partial Denture

Group 1: Traditional gold-containing solders (JELENCO).

Group 2

Soldering – Special solders

Pre-soldering
Used for joining the components before porcelain application.

Post-soldering
Used for joining the components after porcelain application.

Read And Learn More: Fixed Partial Denture Short Essay Question And Answers

Pre-ceramic solders

• Are high-fusing alloys, with temperature slightly beneath the softening point of the parent alloy to be joined and should flow well above the fusion range of applied porcelain
• Solder flow is increased by the addition of silver and decreased by the presence of copper.

Postceramic solders in Partial Denture
Should flow well below the pyroplastic range of the porcelain.

Composition of solders in Partial Denture

Gold, silver, copper, zinc, and tin.

Requirements of solder in Partial Denture

• Should resist tarnish and corrosion
• The fusion temperature of solder should be lower than metal
• Should be free-flowing with proper adhesion to metal
• The solder should not cause pitting of the soldered joint
• The strength of the solder should be equivalent to the parts to be soldered
• The color of the solder should match the parts to be soldered
• It should be corrosion-resistant
• It should have adequate mechanical properties to withstand the forces
• It must have a low surface tension when molten.

Soldering Techniques in Partial Denture

• Torch soldering
• Oven soldering
• Electro-soldering
• Microwelder/laser welding
• Infrared soldering.

Torch soldering in Partial Denture

• After preheating the assembly a gas-air torch is used as the heat source to melt the solder. The flame is kept moving to prevent uneven heat distribution
• Oxidization of the joint surfaces is prevented by using the reducing zone of the flame and by applying an appropriate flux.

Soldering Advantage in Partial Denture

• Solder flow is controlled and solder flows to the hottest point only
• Ideal for badly designed connectors in wax, which can be connected well by varying the temperature of the solder manually.

Advantages of oven soldering/electro-soldering over torch soldering

• Temperature is uniform throughout the procedure
• The temperature is known throughout the procedure
• The application of a vacuum can control oxidation
• Close monitoring is possible.

Electro-soldering Technique in Partial Denture

• Easier to use than torch soldering
• Permits the use of very high fusing alloy solders.

Laser welding in Partial Denture

• Used for joining cast titanium components in implant superstructures.

Infrared soldering in Partial Denture

• Can be used for low-fusing connectors as well as for pre-ceramic soldering
• A pointer is used to direct the heat source to the connector after the application of flux
• While activating the infrared heat source, a protective shield to prevent eye injury is used.

Fluxes in Partial Denture

Fluxes containing fluoride must be used.

Soldering investment in Partial Denture

• Gypsum and phosphate-bonded investments containing fused quartz with low thermal expansion are used as casting investments
• Invested units should expand at the same rate as the castings.

Soldering in Fixed Partial Denture

Pre-ceramic soldering in Fixed Partial Denture

Advantages in Fixed Partial Denture

• The connected prosthesis can be tried in the mouth in the unglazed state
• Adjustments can be made before the final glazing.

Disadvantages in Fixed Partial Denture

• Needs support to prevent high-temperature deformation or sag on long-span
• Difficult to contour the proximal embrasures.

Postceramic soldering

• Indicated when regular gold and metal-ceramic units are being combined
• Final staining and glazing must be completed before the soldering.

Advantages in Postceramic soldering

• Proximal areas are more esthetic as they are shaped before soldering
• Sag does not occur and hence, support is not required.

Disadvantage in Postceramic soldering

Adjustments cannot be made after soldering, if made they need to be reglazed and resoldered.

Soldering steps in Fixed Partial Denture

• Preparation of connector.
• Occlusal soldering index.
• Investing.
• Wax removal and preheating.

Preparation of connector

• After removing surface oxides from the connector surfaces with a stone, evaluate the seating of restoration in the mouth or cast
• The soldering gap should be 0.25 mm.

Occlusal index

• Can be made using plaster, resin or zinc oxide eugenol (ZOE) in a small tray or on a sheet of base plate wax
• The index should not cover the margins and the margins should be exposed prior to investing.

Investing in Postceramic soldering

• The cervical aspect of the restorations is placed into a warmed wax sheet and sealed along the axial wall to protect the porcelain from contact with the soldering investment
• After sealing the porcelain, the entire assembly is boxed and filled with soldering investment, forming into a patty on a slab
• The restorations are seated angled forward so the solder can be placed above the joint.

Wax removal in Postceramic soldering

• After the investment has been completely set, remove the index by placing it in boiling water
• Flow a little flux into the joint space while the soldering block is still warm
• The joint space must be free of investment
• Acrylic resin indexes are removed by heating slowly to 300°C till the resin is burned out heat the block to 650°C and then transfer it to the soldering oven for soldering.

Preheating in pre-ceramic soldering

Preheat the investment in a burnout furnace to 650°C for low-heat soldering and 850°C for pre-ceramic soldering.