Some mechanical characteristics of amalgamators.

IT HAS been well established that the characteristics of dental amalgams are subject to wide variation as the result of changes in formulae, manufacturing methods, and trituration and packing procedures. Trituration and packing procedures are under the control of the operator. In any given alloy we expect to find that undertrituration will produce low crushing strength, high flow and higher than normal expansion in finished amalgams. The proper amount of work applied during amalgamation will provide acceptable expansion (3-13 microns per cm.) and less than 4 per cent flow in all alloys "Certified" to the Research Council of the American Dental Association. Overworking will increase flow values and will decrease expansion if it does not actually cause shrinkage in the final fillings. The susceptibility of alloys to such changes may vary widely from one product to another, some being markedly stable compared with others, but variations of 15 per cent in the mercury-alloy ratio have been shown by Phillips and Boyd' to have marked effects on the properties of amalgams and presumably variations of 10 per cent may be significant. In recent months there appears to have been an increasing interest ill mechanical amalgamators. Individuals are undoubtedly led to consider these devices because of their desire to do this type of work as easily and conveniently as possible, and in many cases it seems that claims for speed and convenience have been so alluring the purchasers have neglected to question the effects of the instruments on the properties of finished restorations. Since the effects of variations in working have been so well established, and further, considering the increasing use of mechanical amalgamators, it appears that every factor governing the use of the instruments should be considered. Mechanical devices to facilitate the amalgamation of alloy particles with mercury for use in dental restorations have been offered the dental profession for many years. The saving of time and the increased convenience have been emphasized. Mechanical amalgamators seldom have been accompanied by adequate directions from either the manufacturers of the instrument or of the alloy, and the user has been left to his own devices in working out a satisfactory method for its use. Under these circumstances we find that some consideration has been given to the effects of mechanical trituration on different types of alloys, but little if any to the mechanical characteristics of the instrument which might vary the amounts of work done and so affect the characteristics of the finished amalgams.