Metal Joining in Dentistry: Soldering, Welding, and Laser Techniques

Metal Joining And Dental Lasers

 

Soldering: Soldering is a process in which two or more metals are joined together by melting and flowing a filler metal (solder) into the joint.

Types of Soldering

There are three types of soldering, i.e.

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1. Soft soldering
2. Hard soldering
3. Brazing

1.  Soft Soldering
   • In soft soldering, there is the joining of two metals by use of a filler metal having a very low melting temperature usually below 350°C.
   • Soft soldering uses a lead—tin alloy as a filer material.
   • As it melts at a very low temperature, it does not generate excessive heat and so it is used in the electronic industry where more heat can lead to the damage of components.
   • Soft soldering is very commonly used by plumbers because of the soft and moldable nature of the filer.

1. • • Here filer is melted by an electronic gun or iron.
     • Soft soldering is unsuitable for application in dentistry as the joint is weak and has a very low load-bearing capacity.
     • These joints lack corrosion resistance.
     • Lead used is hazardous to health and is contraindicated for use inside the oral cavity.
2. Hard Soldering:
   • In hard soldering, the joining of two metals is done by the use of a filer metal that has a melting temperature of less than 450°C.
   • Hard soldering needs a heat source that can generate a medium temperature such as a gas torch.
   • Hard soldering generates a strong joint, so this type of soldering is commonly used in dentistry as well as in other fields such as jewelry, food cans, and the refrigeration industry.
3. Brazing:
   • Brazing is a procedure in which there is joining of two metals together by fusion of filler metal between them having a melting temperature of more than 450°C.
   • It provides the strongest joints but also requires the highest temperatures to melt the filler metal.
   • It needs a very high-temperature source from specialized equipment, i.e. carbon arc torch and goggles to protect the eye from high heat and bright light.
   • It is mainly used in the repair of cast iron objects, in making wrought iron furniture, and in the automobile industry.

Steps in Soldering:

• Clean and assemble the surfaces which are to be joined.
• A proper gap should be maintained between the surfaces which are to be soldered.
• A suitable flux as well as solder is applied to the joint.
• Heat should be applied by a gas torch to the parts which are to be joined.
• Reducing zone of flame is used and solder should be heated till it becomes cherry red.
• Cleaning and polishing of the joint should be done.

Clinical Applications of Soldering:

• For soldering various wires in orthodontics.
• In pedodontics for constructing various space maintainers.
• In fixed prosthodontics:
  • For joining various components of fixed partial
    prosthesis
  • For repair of perforations in crown and bridges
  • To develop a contact point in the crown
  • For cutting and re-joining an ill fitting distorted bridge.
• In removable partial prosthodontics for soldering of clasps.

Welding:

Welding is the process by which two pieces of similar metals are joinedtogether without the addition of another metal.

Types of Welding:

1. Cold welding: In this type of welding, there is no use of heat. This is carried out by hammering or pressure, for example, Gold foil filing
2. Hot welding: In this type of welding, the heat of enough intensity should be used for melting the metals which are joined. This heat source can be from an oxyacetylene flame or high amperage electric current.

Methods of Welding:

Spot Welding: The apparatus which is used for spot welding is known as an ortho- deontic spot welder.

• Clean the parts which are to be joined.
• It should be checked that the surfaces of electrodes are smooth, flat, and perpendicular to the long axis. Both ends should be in proper contact with each other.
• Welder settings should be adjusted as per the manufacturer.
• The proper electrode should be selected. For thin material broad electrode is used and for thick material narrow electrode is used.
• As this is done, this causes an even distribution of weld nuggets.
• Weld mates should be inserted between the electrodes and should be closed together, press the switch to allow a large current to pass through the pieces.
• A combination of heat and pressure will join metal pieces together. This welding is known as spot welding.

Pressure Welding: If two metal parts are placed together and sufficient large force is applied perpendicular to the surface, pressure welding occurs, for example, Pure gold and gold foil.

Laser Welding: In laser welding, the beam is focused at the joint to melt the opposing surfaces. The two liquid surfaces contact and form a weld on solidification.

Applications of Welding:

• In orthodontics to join flat structures like bands and brackets.
• In pedodontics, to weld bands and other appliances.
• In prosthodontics, to join wrought wire clasps and repair of broken metal partial dentures.