The Development of Dental Amalgam
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The Development of Dental Amalgam Cavity fillings were not developed until the early middle ages. Before that, tooth extraction as practiced in ancient Greece and elsewhere was the only treatment available for toothache. In the early middle ages, dental fillings were made from resin, wax, or gum. By the late middle ages, lead and gold leaf metals came into use. In the mid-1850s, a new and very effective technique was developed: gold foil was first heated in an alcohol flame to free it of surface contaminants and make it weld to itself, and then layers of the metal were inserted into a prepared cavity. The layers were then cold welded and hardened by strong compression. The compression process was carried out with a slightly blunt hand-held tool. The physical strength of the practitioner was important, and blows struck with specially designed mallets were used to aid in the process of compacting the gold filling. When electricity came into use, electric-powered mallets were devised. By the end of the 19th century, a dental student was expected to learn a great deal of practical metallurgy. American System of Dentistry, a textbook by W. F. Litch dating from the 1890s, includes a lengthy illustrated chapter on the preparation and use of gold foils, and included passages such as "Purity of gold imparts to the foil the extreme softness it should possess and gives it the facility of being easily adapted to the surfaces of the cavity...any fmetal impurity]... impairs its ductility [malleability] and also causes it to harden more quickly by the application of instruments upon it than if it were absolutely pure." The author also speculated about the possible atomic-scale mechanisms by which heating improved the cohesiveness of gold foil. Amalgams are alloys of mercury. Dental amalgam, an alloy of silver and tin and sometimes other metals with mercury, was first introduced as an alternative to gold foil fillings in the 1820s, but its use was not accepted into dental practice until much later. Amalgam is prepared by mixing fine particles of silver/tin alloy with liquid mercury at room temperature. This pasty mixture is quickly inserted into the cavity where it then hardens rapidly. Many nineteenth-century dentists were concerned that mercury might leach from an amalgam filling over time and cause poisoning. The earliest practitioners to
use dental amalgam were written off as quacks by the dental profession, partly because the technique was taken up by itinerant charlatans who sometimes prepared the material by scraping shavings from coins. Improperly prepared amalgam generally led to a high frequency of failure. If the composition and preparation of the alloy were not carefully controlled, the resulting filling might swell upon setting and cause extreme postoperative pain. The controversy over the use of amalgam among the members of the American Society of Dental Surgeons became so intense that the society actually divided and disbanded in the 1850s. Up to that time, opinions on the matter were formed solely on the basis of
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