Marginal degradation of two amalgams with different creep properties was studied as a function of clinical variables. The amalgam with the highest creep values showed the most marked marginal degradation, irrespective of operator, doubling of the trituration time, and the use of contralateral, opposing, or unrelated teeth for comparison.
Corrosion of base metal alloys was studied by placing the alloys in artificial saliva for 2 months and then determining the concentration of metal ions in the saliva. The distribution of the attack on the surface was examined. The results indicated that the amount of metal ions in the artificial saliva could be related to the Cr content of the alloy. When the Cr content exceeded 16% very little corrosion was observed. The corrosive attack was located at Cr depleted areas, grain boundaries. The Cr depletion probably resulted from coring during solidification.
Creep measurements were performed on different types of amalgams as a function of heat treatment after specimen preparation before testing. The types of amalgams included lathecut, spherical, nonpreamalgamated amalgams, and an amalgam containing Ag-Cu particles. Heat treatment significantly reduced the creep of all alloy types studied. Creep reduction was associated with the phase and transformation gamma1 leads to beta1 (Ag-Hg), which was detected by metallographic and microprobe analysis.
ABSTRACT— Both Cu amalgam and Sn‐containing Ag amalgam alloys with Cu contents ranging from 2 to 30% were used in the investigation. The amalgams were placed in artificial saliva and the content of the dissolved Cu was determined after 1 month. The amalgam remained in the saliva for another 5 months. After the amalgams were removed from the solution, metallographic and microprobe examinations were made. The Cu amalgam released about 10 times more Cu to the artificial saliva than any of the other amalgams. The dispersion type amalgams showed a relatively large dissolution of Cu, while a smaller release was found from amalgam made of powder with one composition. The phases that appeared to be corroded first were γ2 and Cu‐Sn phases. In dispersion type amalgams the γ phase appeared to be attacked. Most of the corrosion products remained inside the amalgam and were identified to be tin oxide chlorides.
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