The mechanism of gingiva metallic pigmentations formation.

The occurrence of blue-grey areas in the soft tissue represents one of the problems affecting patients whose teeth have been restored using metallic materials. It is generally accepted that it is caused by mechanical penetration of a metallic material into the soft tissue. Several facts indicate that this mechanism is not general. The aim of the study was to determine an alternative mechanism of the origin of pigmentations, based on the corrosion interaction of metallic materials used in prosthodontics with the oral environment. The study was comprised of an analysis of pigment particles, determination of exposure conditions of metallic materials in vivo and laboratory evaluation of corrosion properties of the studied materials. Particles containing silver, sulphur and/or selenium could be seen in ultra-thin sections in the lamina propria gingivae. Comparison of the corrosion laboratory results with the results of in vivo measurements indicated the intensification of corrosion under these conditions. Amalgams and silver-containing alloys used for teeth restorations may release silver under the conditions of the oral cavity. The formation of soluble silver compounds in the sulcular area or in a crevice between the crown and the cast post-and-core reconstruction facilitates their transport to the soft tissue and subsequent deposition.

Corrosion behavior of palladium-silver-copper alloys in model saliva.

OBJECTIVES: Palladium-silver system alloyed with other metals represents one of possible material choices in prosthetics. Its corrosion properties are influenced by minority components added in order to obtain the properties required for stomatological purposes. The objective of this work was to ascertain the influence of copper on the corrosion mechanism of palladium-silver alloys. METHODS: Corrosion properties of four palladium-silver-copper alloys were compared with the behavior of the palladium-silver binary system. Standard electrochemical measurements in a model saliva solution were complemented with an XPS analysis of the specimens surface. Experimental data were compared with the results of thermodynamic analysis. RESULTS: The foregoing study revealed formation of a saline layer of insoluble silver compounds as the dominant feature of the corrosion mechanism in a binary system. This process is suppressed in ternary alloys where electrochemical reactions of copper take place on the alloy-electrolyte phase boundary leading to the formation of a layer based on copper oxides. SIGNIFICANCE: The alloying of the palladium-silver binary system with copper results in an important change in the corrosion behavior of ternary alloys. A change in the mechanism of interaction with the environment leads to susceptibility to non-uniform corrosion.