Aren't they rejected sometimes?

There is no immunologic rejection of titanium implants. Commercially pure titanium is perfectly biocompatible and is accepted by the organism. This does not mean that it has a 100% success rate, but a failure is manifested as light mobility and a sensitivity around the implant. The implant is removed in such situations and may be replaced with another implant after healing. Inflammatory reactions (osteitis) leading to substantial pain are extremely rare.

Dr.Florentino Encarnacion G,
Oral Surgeon/Implants Prosthesis Speciallist.
Dental Implants Santo Domingo, Dominican Republic.

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