Modern Methods for Assessing the Corrosion Resistance of Dental Alloys Used in Dentistry

The corrosion process involves a sequence of reactions in which a metal or an alloy is attacked by an aggressive agent [4, 13]. Due to their particular electronic structure characterized by the presence of free electrons in the crystalline network, metals and alloys react chemically or electrochemically and thus may suffer corrosion processes [13, p.85]. The stabile chemical state of the metals is the combined one (oxides, hydroxides, other components) as they appear in the ore from which it was derived. In other words, the metals have a spontaneous tendency to return in a thermodynamically stable combined state through corrosion. Chemical Corro‐ sion is the destruction of metallic materials after direct chemical action to occur without an environment changed by the electric charges. The products resulting from the interaction between the metal and environment remain on the metal surface in formats of thin films. The initial oxide layer/film has a thickness of 10 to 20A0, and then corrosive attack depends on its physical properties such as adhesion, compactness, porosity and the volume of this layer in relation to the volume of metal. The nature of the parent metal is determining both the thermodynamic stability and the properties of the oxide film formed on its surface. Some alloys have a corrosion resistance higher than that of the technical metals through their alloying elements (Al, Cr, Ni, Si) which allow the formation of protective oxide coatings. Electrochem‐ ical corrosion represent destructive attack on metals or alloys exercised by the corrosive environment through electrochemical reactions, in which the metal releases electrons and its positive ions enter in solution. The formation of positive ions and electrons create an electrical potential (in volts) called electrode potential [28, 29].