JOURNAL OF MATERIALS SCIENCE: MATERIALS IN MEDICINE 11 (2000) 287±293 Galvanic corrosion behavior of titanium implants coupled to dental alloys M. CORTADA, LL. GINER, S. COSTA Facultad de Ciencias de la Salud, Universidad Internacional de Catalun Äa, Campus de San Cugat del Valle Ás, Barcelona, Spain F. J. GIL, D. RODRI Â GUEZ, J. A. PLANELL Dept. Ciencia de los Materiales e IngenierõÂa Metalu Ârgica, E.T.S. Enginyeria Industrial de Barcelona, Universitat Polite Ácnica de Catalunya, Spain E-mail:gil@cmem,upc.es The corrosion of ®ve materials for implant suprastructures (cast-titanium, machined- titanium, gold alloy, silver-palladium alloy and chromium-nickel alloy), was investigated in vitro, the materials being galvanically coupled to a titanium implant. Various electrochemical parameters E CORR ,i CORR Evans diagrams, polarization resistance and Tafel slopes) were analyzed. The microstructure of the different dental materials was observed before and after corrosion processes by optical and electron microscopy. Besides, the metallic ions released in the saliva environment were quanti®ed during the corrosion process by means of inductively coupled plasma-mass spectrometry technique (ICP-MS). The cast and machined titanium had the most passive current density at a given potential and chromium-nickel alloy had the most active critical current density values. The high gold content alloys have excellent resistance corrosion, although this decreases when the gold content is lower in the alloy. The palladium alloy had a low critical current density due to the presence of gallium in this composition but a selective dissolution of copper-rich phases was observed through energy dispersive X-ray analysis. # 2000 Kluwer Academic Publishers Introduction Corrosion manifestations on dental alloys may exhibit biological, functional and aesthetic effects, of which the biological effects are of greatest signi®cance. In corrosion processes metal ions are released and may come into contact with cells and tissues in the close environment, or be distributed throughout the entire body. If these ions are not biocompatible, the organism may be injured (toxicity and risk of sensitization). Therefore, the ultimate goal must be to only use those alloys with minimal metal ion release [1]. Titanium was chosen as an implant material primarily on account of its inert behavior towards hard tissues, with the formation on its surface of a direct bony accretion, which was described as an osseointegration phenomenon [2±5]. While it is unanimously agreed that titanium has proved its qualities as a material for endo-osseous implantation, the choice of a suitable alloy for the suprastructure remains an open subject of study. Thus this choice has to be made by taking into account the corrosion resistance when the alloy is coupled with titanium, the biocompatibility, and the clinical studies of the relationship between the metal and the epithelium or the subepithelial connective tissue or bone tissues [6]. In vitro electrochemical techniques have been proven to be suf®ciently sensitive to measure even a low corrosion rate, moreover they are quick and convenient and are now used by many researchers [7±11]. The aim of this article is to compare the corrosion behavior in arti®cial saliva solution of ®ve suprastruc- tures materials at 37  C and to investigate the effects of chemical composition on their corrosion behavior. By means of inductively coupled plasma-mass spectrometry to determine the types and amounts of metal ions released from these couples and based on these data, recommendations can be made for connecting titanium implants to different alloy suprastructures for the health and comfort of patients. Material and methods The chemical composition of the titanium and the dental alloys studied is given in Table I. Five samples were tested in the form of small cylinders (2 mm diameter and 3 mm height) connected to a stem in order to establish the electrical contact for each dental material studied. They were polished metallographically with diamond paste from 5 mm to 0.1 mm. Titanium implant and dental alloy couples were kept immersed in the electrolyte for all the measurements taken. The electrolyte is an arti®cial saliva at a temperature of 37  C and pH 6.7 with the composition given in the Table II. 0957±4530 # 2000 Kluwer Academic Publishers 287