Properties of Dental Amalgams Made from Spherical Alloy Particles

¹ Dental Research Section, National Bureau of Standards, Washington, D.C.

An experimental dental amalgam alloy was prepared in spherical particle form and separated into eight size ranges by means of sieving and elutriation. Using standardized testing procedures, the physical properties were determined on amalgam specimens made from individual size ranges and mixtures of size ranges of spherical particles and, as controls, from three commercial alloys.

Particle size affected dimensional change during setting, residual mercury content, flow, compressive strength, and setting time in the following ways: (1) an increase in particle size increased the amount of expansion during setting and the length of time needed to attain final set; (2) an increase in particle size decreased the residual mercury content; (3) particle size had no significant effect on flow after hardening had been completed; and (4) particle sizes 15-30 µ in diameter gave the maximum strength at all time intervals tested, and all particle sizes under 50 µ gave high early strengths.

Laboratory tests have shown that amalgam can be made from spherical alloy with physical properties as good as, or better than, the alloys currently in use. The main advantages of the spherical alloy over the conventional-type alloy follow: (1) control of physical properties by suitable blending of particle size; (2) less sensitivity to manipulation variables; (3) less flow; (4) higher early compressive strength; and (5) an additional advantage may be a simplification of the manufacturing process.

This initial work with spherical-shaped dental alloy indicates the need for further study and investigation of amalgam employing alloy in this form.