Tribocorrosion Resistance of Dental Implant Alloys—Assessment of cp-Ti, Ti6Al4V, and NiCr in Neutral and Acidified Saliva

Saliva is a potentially aggressive environment due to the presence of acids, chloride, and pH variation, thus the dental implant system can be subjected to corrosion in this medium. Due to masticatory loads during chewing, the joint of implant rehabilitation is subjected to relative micromovements among components leading to a microgap formation and wear. Furthermore, dissimilar alloys in contact at joint interface of dental implant system can potentially drive to electrochemical galvanic couple occurrence. Torque relaxation can be enhanced by corrosion caused by the infiltration of saliva in the microgap. This study aimed to evaluate the influence of saliva and its pH variations on corrosion and tribocorrosion of alloys employed in dental implant system. NiCr, cp-Ti, and Ti6Al4V alloys were evaluated through electrochemical tests in artificial saliva at pH 3.0 and 6.0. The possible occurrence of the galvanic couple for a 3:1 area ratio and their effects were also verified by electrochemical measurements. SEM and confocal microscopy were used for the analysis of worn surfaces. Corrosion polarization tests did not indicate the potential occurrence of galvanic corrosion in saliva. NiCr was more susceptible to localized corrosion and more resistant to tribocorrosion in acidified and neutral artificial saliva than titanium-based alloys. Coupled alloys did not present differences in tribocorrosion performance when compared to each isolate alloy in neutral saliva, pH 6.0. For pH 3.0, Ti6Al4V remained on a passive potential range during sliding when coupled to NiCr, while the other materials were not affected by the galvanic couple condition.