dr shabeel pn SOLDERING

DEFINITION Soldering involves joining two components of metal with an intermediate metal whose melting temperature is lower than the parent metal.

REQUIREMENTS OF A SOLDER Fuse safely below the sag or creep temperature of the parent alloy. Resist tarnish and corrosion. Non pitting. Free flowing. Match the color of the parent metal.

COMPOSITION OF SOLDERS Gold Silver Copper Tin Zinc Gold solders are designated by fineness.

SOLDERING FLUX Flux means flow. Improve the flow of a metal Chemicals that limit the flow of metals are called antifluxes

FUNCTIONS OF A FLUX PROTECTOR It covers the metal surface and prevents oxide formation. REDUCER It helps to reduce the oxides present on the metal surface. SOLVENTS It dissolves any oxide presence and removes it.

COMPOSITION OF A FLUX Borax glass Boric acid Silica

ANTIFLUX Used to control the flow of the metal. Most common anti-fluxes used is graphite. Better fluxes like Rouge in chloroform can be used.

SOLDERING INVESTMENT This are silica –bonded investments that fused quartz. Fused quartz is used because it is the lowest thermally expanding form of silica.

SOLDERING FOR METAL CERAMIC RESTORATION It is usually done prior to ceramic application hence it is also known as pre ceramic soldering. Post ceramic materials are also available.

Pre ceramic soldering is done at a temperature of 1075 to 1120 degree celsius whereas post ceramic soldering should be done at a temperature of 920 degree celsius because ceramic may begin to sag at higher temperatures.

Post ceramic soldering should be done after ceramic firing. Ceramic portions should be finished only afetr soldering.

ADVANTAGES OF PRE CERAMIC SOLDERING The metal framework can be soldered and tried in prior to ceramic build up. Minor casting errors can also be patched up during ceramic build up.

DISADVANTAGES OF PRE CERAMIC SOLDERING Difficult to build ceramic on already soldered units.

ADVANTAGES OF POST CERAMIC SOLDERING Porcelain can be properly build up due to better access.

DISADVANTAGES OF POST CERAMIC SOLDERING The metal and porcelain may sag at high soldering temperatures. It is more technique sensitive. The solder should be re-glazed and re-fired.

OVEN SOLDERING Performed under vacuum or air. A piece of solder is placed in the joint space and it is heated to a standard temperature in the furnace. Superior joint strength.

DISADVANTAGES The parent metal will sag or melt if heated for o long time.

TORCH SOLDERING Soldering is done under direct flame. A gas air torch is used for this purpose. The torch flame has two parts – the reducing part (is at a higher temperature) and the soft brush part.

The solder should be melted using the soft brush flame. The flame should be constantly swiped over the solder for a period of 4 -5 minutes. At no point of time the flame should be held in a stationary position.

INFRARED SOLDERING Used for low fusing connectors. Good accuracy. Similar strength as conventional soldering. Protective eyewear is necessary.

LASER WELDING Done to join Ti components of dental crowns, bridges and partial denture frame works. Pulsed high power Neodymium lasers are used. Low thermal influence preferred in dentistry. Superior joint strength.

SOLDERING TECHNIQUE The design of the connector is determined while fabricating the wax pattern. All the solder connectors require about 0.25mm parallel spaced between the parent components. The smaller units are inserted separately in the mouth.

A thick mix of quick setting plaster is molded over the inserted units. Once the plaster sets, it is removed along with the inserted units. Plaster index is inverted. Components of the prosthesis will be visible.

A triangular piece of utility wax should be placed to index restoration inorder to shape the soldering assembly. The units are invested and the investment is allowed to bench set. Invested wax is eliminated using boiling water or chloroform.

Area of the restoration surrounding the joint should be coated with anti-flux. After coating the flux and the anti-flux, the assembly is preheated in a burnout furnace. Connectors are soldered using a torch or a furnace.

DISADVANTAGES Not economical.

CERAMIC/ACRYLIC VENEERING The ceramic or acrylic veneers in metal resin or metal ceramic restorations are usually added after soldering. Ceramic veneering is done in 3 steps 1. METAL PREPARATION. 2. PORCELAIN APPLICATION. 3. PORCELAIN FIRING.

METAL PREPARATION Any minor casting defects in the cut back area should be corrected. Recovery includes sand-blasting and ultrasonic cleaning. The gingival surface of the pontic should be reduced. Gingival surface of the pontic should always be covered with porcelain.

PORCELAIN APPLICATION After preparing the metal, an opaque layer of porcelain should be applied over the metal surface. Gingival surface of porcelain is coated with cervical porcelain. Layer of cervical, body and incisal porcelains should be used to build up the facial surface.

Porcelain in the interdental area should be sectioned to demarcate junction of the two units. A separating liquid is applied over the edentulous ridge prior to building up the gingival surface of the pontic.

PORCELAIN FIRING Next the porcelain is fired as per the manufacture’s instruction. After firing the core porcelain, glaze porcelain is added and fired as usual.

ACRYLIC VENEERS Similar to ceramic veneering except for a few differences. Major difference is that only mechanical bonding exists between the metal and resin. Bond strength is considerably less.

PROCEDURE Mechanical undercuts can be created by sprinkling plastic retentive pearls over the wax pattern before casting. The surface of the cast metal can be roughened using Al2O3 air abrasive unit. A small quantity opaque resin is added onto the metal surface. Body shade resin is added over the opaque resin and contoured using a modelling instrument.

The resin should be polymerised under pressure in a warm water bath The resin should be polymerised under pressure in a warm water bath. Light cure resins are also available. Resin core should be carved to remove excess material. Space should be provided to accommodate incisal shade resin.

Finally incisal shade resin is added and contoured. After polymerization, the restoration is finished and polished

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