SOLDERING

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SOLDERING
dr shabeel pn

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DEFINITION

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

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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.

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COMPOSITION OF SOLDERS

• Gold
• Silver
• Copper
• Tin
• Zinc
• Gold solders are designated by fineness.

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SOLDERING FLUX

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

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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.

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COMPOSITION OF A FLUX

• Borax glass
• Boric acid
• Silica

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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.

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SOLDERING INVESTMENT

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

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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.

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• 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.

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

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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.

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DISADVANTAGES OF PRE CERAMIC SOLDERING

• Difficult to build ceramic on already soldered
  units.

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ADVANTAGES OF POST CERAMIC SOLDERING

• Porcelain can be properly build up due to better
  access.

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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.

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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.

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DISADVANTAGES

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

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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.

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• 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.

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INFRARED SOLDERING

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

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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.

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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.

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• 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.

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• 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.

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• 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.

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DISADVANTAGES

• Not economical.

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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.

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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.

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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.

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• 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.

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PORCELAIN FIRING

• Next the porcelain is fired as per the
  manufactures instruction.
• After firing the core porcelain, glaze porcelain
  is added and fired as usual.

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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.

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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.

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• 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.

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

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  THANKING YOU