Corrosion Behaviors of Titanium and Coexisting Dental Alloys

Abstract

Titanium has been widely used for dental implant owing to its superior biocompatibility and corrosion resistance. However, metal restorations involving the superstructure of the implant, bridge, crown and inlay are usually fabricated from alloys other than titanium. It is well known that electrochemical corrosion may be caused by galvanic reaction between the different alloys in contact with each other in an electrolyte, resulting in preferential corrosion of the electrochemically base metal. It is therefore recommended that dental restorations be designed not to bring different alloy systems in contact within an individual mouth, in order to avoid galvanic reaction. On the other hand, the corrosion behaviors of different alloy systems are still unclear when they coexist without being in contact. The present study examined the potential electrochemical corrosions of pure titanium and other dental alloys coexisting in contact or without contact in 1.0% lactic acid aqueous solution for 36 weeks. Little or no changes were seen in dissolutions of Au-Pt-Pd ceramo-metal alloy and titanium when they were immersed together, regardless of the contact. The amount of released Cu from the Au-Ag-Cu alloy tended to increase slightly in the presence of titanium, and the amount of Ti also increased. When the Au-Ag-Pd alloy and titanium coexisted, the release of Ag significantly decreased and Cu and Ti increased. There were no significant differences whether they were in contact or not. Marked dissolutions of Ag, Zn, Sn and In were found in the case of the Ag-Zn-Sn-In alloy specimen even if immersed alone. When titanium and the alloy were in contact, the releases of Ag and Ti were restrained while In was released to a greater degree. The same tendencies were found even when they were not in contact. With the Co-Cr alloy, Co was most released and its release was significantly accelerated in the presence of titanium. The release of Ti tended to show an increase both in the cases of contact and non-contact. In conclusion, any combination of titanium and dental alloys except for the ceramo-metal noble alloy exhibited galvanic corrosion, even if they were not in contact. These results suggest that titanium implants should be designed with due regard to total biocompatibility to prevent the possibility of increased release of allergic or toxic constituents from existing alloy restorations in the mouth.