Biological incompatibility of these ions can produce body injury, causing toxicity and risk of sensitization therefore, it is fundamental the use of alloys made up of metals with a low degree of ionic. During corrosive processes, metal ions are freed into the medium and come into contact with neighbouring tissues and/or are spread throughout the entire body. The consequences of corrosion in alloys for dental use may result in negative biological, functional and aesthetic effects, of which the biological ones have higher significance. Given the nature of the medium in the oral cavity, it is especially important that the materials used show a high electrolytic corrosion resistance. It produces unintended wear of the metal surface, and a deterioration of the outer and inner layers caused by exposure to chemicals or electrochemical reaction of the surrounding area. Electro-chemical corrosion is the most important injury factor in dental work. Furthermore, Poljak-Guberina pointed out the need to study processes which may enable to line or coat non-noble materials with higher corrosion-resistance ones, which will improve the behaviour of these alloys in the oral environment. In order to improve corrosion resistance and “make them nobler” Sarantopoulos studied two alloys ( Noble Crown ® and Noble Crown NF ®) made with the last two pairs of non-noble metals to which palladium was added, thus he concluded that the inclusion of this element has deleterious effects upon the physico-chemical properties of both alloys. For their part, as it has been shown, gold and palladium-based alloys present a lower dissolution rate and therefore greater corrosion resistance than those made up of non-noble base metals such as nickel- chrome or chrome-cobalt. These authors observed a differential resistance to corrosion depending on the composition of each of the alloys used, despite the fact that all of them largely contain gold and palladium.
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analysed resistance to corrosion of four noble alloys (Pontor 2 ®, Cerapall 2 ®, V-Gnathos Plus ® and Pagalin ®) and of a titanium alloy (Ti6Al4V) attached to commercially pure titanium (c.p. The different metallic materials used in such alloys have yielded varied results. Alternatively, newly developed alloys attempt to reduce corrosion without risk of losing the right physical properties. Due to their high cost, noble or semi-noble alloys with high content of gold and palladium, represent a problem when used to produce fixed prostheses over implants.