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A new motion picture in color, entitled "Dental Amalgam--Failures Caused by Moisture Contamination," has just been completed at the National Bureau of Standards. This fihn, prepared under the joint auspices of the Bureau and the Research Commission of the American Dental Association, is the second of a series of technical films prepared for dental and allied professions.
The dental amalgam film demonstrates one of the most common causes of amalgam failure--namely, contamination with moisture. This contamination with moisture is usually produced by mixing amalgam in the palm of the hand and by condensing amalgam in a wet field. The moisture introduced into the amalgam reacts with the alloy to produce hydrogen gas which causes excessive expansion, lowers compressive strength, and forms blisters. Clinically, contamination of amalgam with moisture is evidenced by expansion causing post operative pain, extrusion of the alloy from the cavity, formation of blisters, faulty margins, and fractured restorations. The film describes a satisfactory technique for the prevention of contamination.
Since 1928 the National Bureau of Standards and the American Dental Association have conducted cooperative research on the physical and chemical properties of dental materials and the proper techniques involved in their use. The present film, the second of a series that will stress the clinical significance of the physical and chemical properties of dental materials and the importance of technique, is a result of this research. The first film, "Silicate Cement," was made available to the dental profession last fall.
The new motion picture on amalgam, a 16-mm. sound film photographed in color, has a running time of 15 rain. The film is available from the NBC : loan or purchase information can be obtained by writing to the Office of Scientific Publications, National Bureau of Standards, Washington 25, D. C. The heavy demands for the silicate cement film suggest that the amalgam film will also be heavily booked: it is therefore advisable that loan requests be made at least 30 days in advance of any projected showing.
A comprehensive investigation of the conditions for the formation of negative atomic ions of the heavier metallic elements has led to the development, by Dr. Willard H. Bennett of the National Bureau of Standards, of an extremely valuable method for detecting, separating, identifying, and measuring such ions--one of the most neglected fields of research in pure physics. Since negative atomic ions, consisting of atoms with extra electrons, have very low energies of formation, their
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