There are examples of the use of gold in dental applications as far back as The Etruscans in the seventh century BC who used gold wire to hold in place substitute teeth, usually from a cow or calf, when their own were damaged. As long ago as 1530 the first printed book on dentistry published in Leipzig recommended gold leaf for filling cavities. The advantages of gold and its alloys for dental applications are its bio-compatibility, malleability and resistance to corrosion. The requirement for good biocompatability of a material is obviously closely related to the corrosion resistance. Thus, when the alloy is placed in contact with the body of the patient, there should be no detrimental harm to health.

Preparing dental gold on bridgework

A number of gold products can be used in dentistry, including pure gold metal (in the form of foil, powder or thin flake like crystals known as 'mat gold'), wrought alloys (in the form of wires and plates), casting alloys and gold alloy solders. In terms of pure gold, leaf is still compressed into pellets and packed into small cavities in teeth that are otherwise sound, with the aid of a hand mallet or mechanical condenser. This restoration has great durability against the chemical attack of oral fluids but the gold must be in cavities exposed to little wear, because it is so soft. This technique is very rarely used nowadays.

So the main application of gold in modern dentistry is alloys, which are a mixture of gold and the noble metals platinum, palladium or silver plus copper and zinc. The aim is an alloy that is easy for the dentist to manipulate but is strong, stiff, durable and resistant to tarnish and corrosion. These alloys are used for inlays, crowns and bridges. The gold content of the alloy will vary according to the precise application. A typical crown and bridge alloy may contain 62-78 per cent gold, with silver, platinum and palladium added to make at least 75 per cent noble metals, plus copper and zinc.

The extensive range of dental alloys are defined in a number of National and International specifications including those of the American Dental Association. By varying the composition of the alloys a wide range of properties can be achieved (yield and tensile strengths, elongation, hardness). Additional elements are also added to improve castability (aiding the manufacture of the dental component) or to control thermal expansion.

Soldering is a particularly important dental technique for the connection of individual components. In metallurgy terms, solder refers to alloys melting below 425°C in contrast to alloys for brazing which melt above this temperature. In dentistry, the generic term soldering is used to cover all such operations. The dental solder alloys are generally based on an alloy of gold, silver and copper with possibly small additions of tin, zinc or nickel.

For an extensive review article on the use of gold in dental applications see a recent Gold Bulletin paper