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Electron microscopic evidence supports previous indirect evidence that the amalgam reaction products nucleate from the liquid between the silver-tin particles. [ABSTRACT FROM AUTHOR]

This article discusses the development of a low temperature method for studying the metallurgy of dental amalgams. The development of micrographic specimens of dental amalgam by quenching the metals in a bath of carbon dioxide and acetone at temperatures of -77° centigrade is described. The advantages of this method for the identification of nucleation sites for reaction product grains are noted.

The technique of accumulating plaque on removable disks in a complete denture provides a convenient method for investigating plaque on artificial surfaces. Examination of the plaque specimen with a SEM indicated that the plaque consists of microorganisms and a nonstructured matrix. This technique provides results that are consistent for a given individual. However, a group of 12 different individuals had a wide range in the thickness and content of plaque accumulations during equal time intervals. Thin plaque accumulations consisted of a filmlike layer with an apparently small number of microorganisms. Thick layers of plaque consisted of relatively large numbers of microorganisms with some intercellular matrix. The thickness of the plaque layer is apparently determined primarily by the number of microorganisms present.

A computer program was formulated and verified experimentally to predict the optical density on an image receptor for any given set of radiographic variables including tube kilovoltage, milliamperage, and wave form; x-ray beam filtration; nature of filters and absorbers, and type of x-ray film.