d. Heat Hardening Treatment (Tempering). This treatment is necessary to
restore to metals properties that are decreased by annealing and cold working. Metals
to be heat hardened should first be heat softened (annealed) so that all strain hardening
is relieved and the hardening process can be properly controlled. Heat hardening is
accomplished in dental gold alloy by heating to 840 Fahrenheit, allowing it to cool
slowly over a 15-minute period to 480 Fahrenheit, and then immersing it in water.
Section II. DENTAL AMALGAM
a. History of Amalgam. Dr. G. V. Black investigated the properties of
amalgams and their possible use for dentistry about 1895. His studies showed the
effects of chemical composition and physical structure on the properties of amalgam
restorations. Due largely to the work done by Dr. Black, the National Bureau of
Standards, and other researchers, amalgam is now used more than any other filling
(1) Alloy. An alloy is a solid mixture of two or more metals. It is possible to
produce a material in which the desirable properties of each constituent are retained or
even enhanced while the less desirable properties are reduced or eliminated. With few
exceptions, the metals used in dentistry are in fact alloys.
(2) Amalgam. When one of the metals in an alloy mixture is mercury, an
amalgam is formed. A dental amalgam is a combination of mercury with a specially
prepared silver alloy. It is used as a restorative material.
(3) Mercury. Mercury is a silver-white, poisonous, metallic element that is
liquid at room temperature (symbol Hg).
(1) Combining desirable properties. Each metal incorporated into a dental
silver alloy has specific properties when combined with mercury. Some properties are
desirable and some are undesirable. An acceptable alloy is balanced. The combined
effects of the properties of its ingredients should provide the most satisfactory
(2) Standards and requirements. Like other restorative materials, amalgam
must meet the standards and requirements set by the National Bureau of Standards
and the American Dental Association's (ADA) Specificationnumber one for alloy used in