Titanium is tought to be the "New Allergen".

 

Increase in the prevalence

of oral allergies to metals,

especially in patients with history of allergy to other metals.

Titanium oral implants can induce toxicity or type I or IV allergic reactions with unexplained failure cases of dental implants

Evrard L WD, Parent D. Allergies to metals. Titanium: a new allergen. Rev Med Brux. 2010

Histological study on retrieved titanium hip implants showed a quite strong inflammatory response 

and was regarded as contribution factor for failure

Lalor PA , Revell, Sensitivity to titanium. A cause of implant failure ? Journal of bone Surgery 2009