The Influence of Precondensation Mercury Content and Mulling on the Transverse Strength of Amalgams Condensed After a Delay

Abstract

The purpose of this study was to investigate the influence of changing the precondensation mercury content (initial mercury content) on the final strength of amalgams when the condensation was delayed. Another purpose was to study the effect on the transverse strength of mulling the amalgam mix after the delay. The material consisted of ten different brands of alloy. Three different alloy-mercury ratios were used with each alloy brand; Mix I about 50% Hg, Mix II about 54% Hg and Mix III about 59% Hg. Rectangular amalgam test pieces, measuring 2 × 2 × 12 mm, were condensed after a 5 minutes delay by hand using a load of about 17 kg/cm². The transverse strength test was performed after one week using three point loading. The five minutes delay of the condensation reduced the strength of the amalgams by 1 to 42 per cent depending on the brand of alloy and precondensation mercury content. The three preamalgamated amalgams were affected less by the delay than the other amalgams. Increasing the precondensation mercury content reduced the effect of the delay on the final strength. The «mulling» of the amalgam mix also decreased the effect of the delay. It was concluded that a moderate excess of initial mercury gives the dentist a longer condensing time thus allowing him to perform the condensing procedure with care.