Galvanic currents between dental alloys in vitro.

The galvanic current densities between gold, amalgam and cobalt-chromium, three different classes of dental alloys, were determined in vitro in artificial saliva kept at 35 degrees C. The maximum current density of 200 microA/dm2 was obtained between the conventional amalgam and a type III gold alloy. Galvanic currents of lesser magnitude could also be measured between amalgams high in copper and the other alloys. No measurable current densities were obtained between gold alloys and between gold and cobalt-chromium alloy with the exception of a casting and a solder gold alloy commonly used in combination.

Galvanic series of some dental alloys.

Galvanic series for different metals in different electrolytes have been published, but never for dental alloys in artificial saline solution. The material classes studied are amalgam, gold alloy, nickel alloy, chromium cobalt casting alloy and temporary crown form. The electrogalvanic potentials were measured and determined in reference to a hydrogen electrode (H2/H+) arbitrarily defined as zero. A galvanic series of the tested materials was arranged in order of their potentials.

Influence of stone mixing agents, impression materials and lubricants on surface hardness and dimension of a dental stone die material.

The influence of different stone mixing agents, impression materials and lubrication methods on the surface hardness of a stone die material has been evaluated. For one impression material the dimensional effect of the mixing agents and lubrication on the dies was also studied. The stone die material was mixed with water or a gypsum hardener and allowed to set on surfaces of glass, agar-agar, polyether, polysulfide and silicone impression materials. The lubrication methods for the stone were mineral oil, water soluble lubricant and mineral oil followed by water soluble lubricant. The surface hardness was measured according to the Brinell test. The Brinell test was chosen after a comparative study of the Brinell, Vickers and Knoop hardness test methods. The results showed that gypsum hardener was preferable to distilled water. The impression materials appear to have influence on the surface hardness of stone. The effect differed on water mixed and hardener mixed stone which emphasizes the importance of the mixing agent. All lubrication decreased the surface hardness of stone. With hardener mixed stone the combination of mineral oil followed by water soluble lubricant seemed preferable. Neither the gypsum hardener nor the lubrication influenced the dimension of the stone die material.