The large variety of dental alloys that exists on the market presents various compositional formula and possibilities of utilisation. It is very important to know the influence of the oral bacteria on dental alloys and, as it was demonstrated in several similar industrial branches, the bio corrosion process takes action and important damages to the metal dental structure may occur [1, 2]. A good evaluation of the corrosion process is connected with a good investigation of the metal alloy biocompatibility [3]. A higher interest is noticed in non-noble alloys (Ni, Cr, Co, Ti), to avoid expensive costs and limited resources of noble alloys. The chemical nature of the metal alloy determines the composition of the superficial films with strong influence to corrosion behaviour in saliva [4, 5]. The electrochemical study of a dental alloy in artificial saliva permits the estimation of modification in alloy properties in the oral cavity, using rapid electrochemical tests as a qualitative criterion to estimate the corrosion resistance [6, 7]. An important feature of corrosion behaviour of the surgical implant of metal alloy was noticed, namely the fact that the cobalt alloys do not show the traditional active-passive transition, as they were in a passive state prior to testing [8].