Measures for Progress: A History of the National Bureau of Standards

272 THE TIDE OF COMMERCE AND INDUSTRY (1920-30)
Hidnert of the Bureau expanded their initial investigation of dental inlay
materials and dental techniques.
Assisted by research associates from private laboratories and prac-
ticing dentists representing the American Dental Association, the Bureau
physicists studied the physical and chemical properties of inlay materials,
amalgams, plasters, and waxes, and began to establish specifications and
standards for dental testing laboratories and manufacturers of dental ma-
terials.15' Prior to this research, rejection of dental materials tested at the
Bureau for the Government had run as high as 50 percent or more. One
Bureau report about to be made public, disclosing that 6 out of 10 dental
amalgams available to the profession were unsatisfactory, and only 4 out
of 10 would stay in any appreciable time if used as fillings, was suppressed
by the Commerce Department lest it result in loss of public confidence.152
By the early 1930's rejections amounted to less than 10 percent. Be-
fore long it became "possible for dentists to use amalgam fillings that [would]
not shrink and drop out, cements that [would] not dissolve, bridgework
that [was] practically permanent, and gold inlays lasting [far beyond the]
3 to 5 years as was the case a short time ago."
A persistent difficulty encountered with certain types of metallic alloys
used for fillings was their tendency to become deformed in use and require
replacement. Interferometry studies disclosed that, extending over a period
of 1 to 4 days, the expansivity of some amalgams was about four times that
of the teeth. For many years the trouble was attributed, in the absence of
other discernible causes, to variations of the alloy from package to package.154
The source of the difficulty, at least in amalgams containing zinc, was
eventually traced to the dentist's office, in the moisture added to the filling
by his palming or hand mulling of the amalgam. The moisture and salt
contamination from the hand, acting on the trace of zinc in the amalgam,
formed hydrogen gas, and in a short time out came the filling.155
Research for the textile industry in the 1920's covered basic investi-
gations into the physical and chemical properties of fibers, yarns, and
fabrics, the conservation of textiles (for the peace of mind of dyers and
cleaners), utilization of low-grade cotton and of waste silk materials, estab-
151 T157 (Souder and Peters, 1920); superseded by C433 (Souder and Paffenbarger,
1942), the latter a résumé of dental research at the Bureau since 1919.
Letter, P. J. Crogan, Bureau of Foreign and Domestic Commerce to F. C. Brown,
Aug. 25, 1926 (NBS Box 179, PA).
NBS Annual Report 1931, p. 43; Annual Report 1936, p. 62; Science, 92, 527 (1940).
NBS Annual Report 1919, p. 148; Annual Report 1922, p. 174; T157, p. 9.
155 Schoonover, Souder, arid Beall, "Excessive expansion of dental amalgam," J. Am.
Dental Assoc. 29, 1825 (1942) -