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.
Preparation and condensation of amalgam with a low mercuryalloy ratio.
An amalgam mass can be triturated in a mechanical amalgamator so that the amalgam contains a near-optimum ratio of less than 50 per cent mercury. Amalgam triturated in this proportion exhibits desirable clinical aspects in condensation and manipulation. There is little or no excess residual mercury to remove, and the operator need concern himself only with proper condensation of the material. Routine clinical use for four years has confirmed the results of laboratory tests.
Mercury Analysis of one Hundred Amalgam Restorations
THE physical properties of dental amalgam depend to a large degree upon the amount of mercury retained in the finished restoration. The deleterious effects of excess mercury have been well proved.'-4 These studies have indicated that excessive mercury allowed to remain in amalgam after condensation markedly lowered the compressive strength and increased the per cent of flow. Reduction in these properties would enhance the possibilities of fracture and distortion. Other research has also shown that tarnish and corrosion occur more readily on restorations containing an excess of mercury.5' 6, 7 These findings have led to the adoption of a technic which would expel all the mercury possible and thus assure maximum strength and resistance to tarnish. Pertinent essentials in such a technic include the use of the recommended mercury-alloy ratio, proper trituration, and correct condensation. The recommended mercury ratio, usually 60 per cent mercury by weight, always calls for more mercury than is required in the finished restoration. This excess is added to make amalgamation easier and to obtain proper adaptation to the cavity preparation. The extra mercury is then eliminated by expressing from the semiliquid mass before condensation and by the packing procedure. The success of the restoration is dependent to a great degree upon the ability of the operator to hold to a minimum the final mercury content. Some investigations have been done to determine the actual per cent of mercury remaining in specimens when various trituration and packing technics were employed.4 8, 9 These studies indicated that the final mercury content might vary from approximately 40 per cent up to 54 per cent, depending upon the manipulative procedure. Since these investigations were conducted on laboratory specimens, the actual mercury percentages might not be comparable to those present in clinical restorations. Souder and Sweeney analyzed two restorations which had been in service for over ten years and found the mercury content to be 51.6 per cent and 52.9 per cent.10 This study also indicated that no significant amount of mercury is lost from the restoration due to slow vaporization or dissolution. However, no one has investigated the residual mercury content in a large number of amalgam restorations. Such data would be of value not only for determining actual mercury content in the average restoration but also for detecting fluctuations which might occur in the use of various manipulative technics. The purpose of this study, therefore, was to determine the mercury content in one hundred amalgam fillings which had been removed from extracted teeth. These teeth were secured from the Oral Surgery Department of Indiana University School of Dentistry. There was, of course, no information available in