The Influence of Precondensation Mercury Content on the Transverse Strength of Amalgams

Abstract

The purpose of this investigation was to study the influence of changing the precondensation mercury content (initial mercury content) on the early and final transverse strength of different amalgams. The material consisted of five conventional lathe cut alloys, two of which were zinc free, of one dispersion strengthened and one spherical alloy and of three lathe cut preamalgamated alloys. The amalgam was mixed with mercury using three different alloy-mercury ratios. Thus the precondensation mercury content of Mix I was about 50 per cent, of Mix II about 54 and of Mix HI about 59 per cent for all amalgams except the spherical brand. Rectangular amalgam test pieces, measuring 2 × 2 × 12 mm, were condensed by hand using a load of about 17 kg/cm². The transverse strength test was performed either after one hour or one week using three point loading. The results show that for some of the amalgams an increase of the precondensation mercury content resulted in a slight reduction of the early strength. Furthermore the results show that the early strength was lower for the preamalgamated amalgams than for the other amalgams. Increasing the precondensation mercury content did not significantly effect the final strength of six amalgam brands but increased the strength of three brands and reduced the strength of one brand. It was concluded that it is safer to use a moderate excess of initial mercury in clinical amalgam work than to try to reduce the initial mercury content as much as possible.