Accuracy of mercury-alloy proportioning systems.
To measure the reproducible accuracy of some commercially available mercury/alloy proportioning systems, a study was made of several mercury dispensers, alloy pellets, and disposable capsules. This study included a consideration of some human variables that were introduced in manipulating the systems. Most of the systems that were tested provided acceptable accuracy when used correctly.
Influences of Clinical Factors on Marginal Adaptation and Residual Mercury Content of Amalgam
Clinical factors affecting residual mercury and marginal adaptations of amalgam restorations in a private practice environment were investigated. Findings, converted to ridit values, indicated that influencing factors are the training level of the dental assistants, type of amalgamator, accuracy of the timing device, and method of condensation.
Residual Mercury Content of Amalgam Restorations and its Influence on Compressive Strength
IT HAS long been thought that the residual mercury content of amalgam restoration does influence, to some extent, both the compressive strength and resistance to tarnish. Ward and Scott,1 investigating primarily the effects of packing pressures on dimensional change, made some observations on compressive strength as related to residual mercury. They noted that when the packing pressures were increased, there was a trend toward higher compressive strengths and lower residual mercury contents. The use of extremely high condensation pressures (256,000 psi) reduced the residual mercury to 28.3 per cent and the compressive strength rose to 73,000 psi. Such pressures are, of course, not possible in the clinical insertion of an amalgam restoration. Gray's original work illustrated that as the mercury decreased below 50 per cent the strength increased. Crawford and Larson3 demonstrated that the compressive strength of amalgam increased from 53,000 psi to approximately 59,000 psi when the residual mercury fell from 48 to 35 per cent. However, they found no correlation between strength and residual mercury within limits of 45 to 50 per cent. Likewise Ryge, Dickson, Smith, and Schoonover,4 were unable to demonstrate any relationship in strength with specimens where the residual mercury ranged from 46.5 to 53.0 per cent. Swartz and Phillips5 detected no influence upon compressive strength of residual mercury between limits of 45.6 and 48.5 per cent. The studies cited were designed primarily to investigate the effect upon compressive strength of minimal amounts of mercury which might be secured by use of heavy condensation pressures. As Crawford has summarized,3 there seems to be little gained, at least in terms of strength, in the development or use of a technic which would reduce the mercury content below 45 per cent. Little work has been done, however, to correlate the strength with the residual mercury at the higher levels that are more commonly found in the amalgam restoration. Analyses of amalgam restorations removed from extracted teeth indicate that mercury is often present in amounts well above 50 per cent. Crawford and Larson3 analyzed 10 restorations and found the residual mercury content ranged from 45.2 to 59 per cent. Souder and Sweeney6 analyzed 2 restorations and found 51.6 per cent mercury in one, and 52.9 per cent