RESEARCH has clearly indicated that the cause of amalgam failures, other X than those due to improper cavity preparation, can no longer be attributed to the use of an inferior alloy, but rather to the improper use of a good alloy.' Specifications established by the American Dental Association have assured the dentist alloys of good physical properties, but all of the properties are seriously altered by certain manipulative variables. The dimensional change, in particular, fluctuates greatly with trituration time, moisture contamination, and packing pressure. A slight undertrituration produces a setting expansion above the upper limit of 13 microns per centimeter, which is allowed by the specification, while a slightly overtriturated amalgam will not expand up to the lower limit of 3 microns. The use of mechanical amalgamators and pneumatic or automatic condensers also reduces the expansion and generally produces an actual contraction of several microns.2 Undoubtedly, many amalgam restorations are being placed daily which do not expand between 3 and 13 microns per centimeter. Some investigators, however, have felt that slight contraction in the amalgam restoration might not be clinically significant and that the increased strength and better handling characteristics associated with a slightly overtriturated amalgam would actually be advantageous.3 In a previous investigation, 34 amalgam restorations were placed in the permanent teeth of child patients by a technic which produced a setting contraction of 2 to 4 microns.4 After a 3-year observation period, there was no definite clinical evidence of contraction and the fillings handled in this manner proved to be slightly superior in terms of roughness and tarnish. The results of this study indicated that a slight contraction or expansion is not clinically significant. Naturally, the tremendous expansion of several hundred microns caused from moisture contamination is quite readily evidenced in amalgam fillings, but the slight deviation induced by a modification of the mixing time might not be clinically important. It should be pointed out that although the dimensional change is generally expressed in terms of microns per centimeter, the actual change across a typical restoration is much less since the width is generally less than 0.5 cm. It was felt that these previous results4 should be exaggerated by the use of a special composition alloy. Since most present popular alloys will not contract more than 10 microns, even with prolonged trituration, a 32 per cent tin alloy was compounded by Baker and Company for use in this study.* The technic for mixing and condensing this alloy was standardized in the laboratory