Identifier: dentalmetallurg00brad (find matches)
Title: Dental metallurgy, for the use of dental students and practitioners
Year: 1917 (1910s)
Authors: Brady, Ewing Paul
Subjects:
Publisher: Philadelphia and New York, Lea & Febiger
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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Fig. 61 1. If the amalgam does not expand sufficiently, it will notbe permanent enough to withstand a sufficient amount ofaging, while in the hands of the dental depots or the dentist,before using. 2. An excess of expansion would cause the filling to bulgefrom its margins. Flow and Crushing Strength.—Suitable molds of definitesize are used to obtain cubes of the alloy. Fig. 61 illustratesa set of these instruments as gotten up by Dr. G. V. Black.The cube is placed in the dynamometer (Fig. 62) and forceapplied by means of the thumb-screw D, the amount of FLOW AND CRUSHING STRENGTH 283
Text Appearing After Image:
Y1Q. 62.—The dynamometer. The instrument in position for use. 284 AMALGAMS force applied is recorded upon the dial H; the flow isrecorded by adjusting the thumb-screw J, and upon readingthe dial K, the amount of flow may be ascertained. According to the experiments made at the NorthwesternUniversity, the average force of mastication as obtainedfrom 1000 cases tested was 171 pounds. Taking this asa standard, amalgams should not show any appreciableamount of flow when this amount of pressure is applied.The result of an excessive flow in an amalgam would be suchthat the permanency of the filling would be impaired, andthis property may be developed to such an extent as tofracture tooth substance. There must be a balance betweenflow and brittleness, as when flow is absolutely lackingbrittleness is developed to such an extent that the amalgamwill be low in crushing strength. The amalgam should possess sufficient crushing strengthin order to withstand the forces of mastication. This proper

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