Of course, it can happen that some bodies react differently than usual to the implantation of a dental implant. Rejection of the implant due to a titanium allergy is extremely rare. However, there is a small percentage of people who are allergic to titanium, but it is less than 1%.
An implant is rejected when it fails to bond with the bone due to infection. In any case, the implant is then removed, leaving a wound that heals quickly.
After that, it is possible to use other materials, with no significant problems for re-implanting the dental implants.