N.W. Rupp

Wear and Microhardness of a Silver-sintered Glass-Ionomer Cement

Knoop Hardness and pin-and-disc-wear measurements were made on a commercial silver-sintered glass-ionomer cement. The objective was to determine whether the incorporation of a bonded-metal-to-glass filler would enhance durability as determined by the above measurements. As with the previous work on conventional (non-metalized) glass-ionomer cements, the specimens were preconditioned at 37°C in air, water, 0.02 mol/L lactic acid (pH 2.67), and heptane. The influence of these media on the microhardness of the silver-sintered material was about the same as that on the conventional materials. Storing in air produced dehydration, which increased the hardness considerably. Heptane storage increased the hardness less, but this increase is attributed to continued curing during storage. After storage in water, the hardness was essentially unchanged; the influence of increased cure is believed to be offset by softening or plasticization from water uptake. Lactic acid produced a decrease in hardness from chemical dissolution as seen from the SEM observations. In most cases, in particular for the air-stored specimens, the wear resistance was enhanced markedly over that of the conventional materials evaluated previously. The exception was the lactic acid-stored specimens for which little, or no, improvement was observed during early periods of wear. The incorporation of silver appeared to provide lubrication, thus reducing wear. However, catastrophic failure from brittle fracture was still a problem, but its occurrence was less frequent.

Dimensional Changes of Four Amalgams After Five Years of Storage in Air at 60, 37, and 23°C:

Amalgam cylinders, 4 mm in diameter and 8 mm long, made from four alloys, expanded lengthwise from 204 to 220 at 60°C, 18 to 46 at 37°C, and 6 to 35 at 23°C, μm/cm, respectively, after storage in air at the indicated temperatures for five yr.

Copper-free Amalgams: Dimensional Change After Approximately Five Years at 60, 37, and 23°C

Two copper-free amalgams expanded excessively after storage in air at 60°C for about five yr. One expanded significantly at 37°C and slightly at 23°C. High silver content, absence of copper, and presence of small amounts of zinc, or all three, seemed to promote very high expansions at 60° C.