The standard ABNT NBR 16044:2012 defines the general requirements for dental implants. It specifies several elements and, among them, the contact between materials of different chemical composition. That standard mentions another (ABNT ISO 21534), which defines that the combination of stainless steel ASTM F138-13a (used as a manufacturing material for intermediate pieces) and of Ti6Al4V (used in the manufacture of implants) is considered acceptable for the application, and can be used without problems. It is worth mentioning that most of the competition already works with chemical-mechanical divergence between the alloys used in the implants (G4) and components (G5). The wear between the faces will exist when both are in diverging movemements, which does not occur due to the rigid indexation promoted by the reliability of the machining process. You can follow the article that validates the safety and resistance of the connection at the link below: https://goo.gl/gGMwBb