The greatest risk is the possible loss of sensitivity of the lower lip, in the unlikely event that the kin nerve is touched or broken during surgery. This sensitivity loss can be temporary or permanent. This is why the surgeon has to be very careful and diligent working around this area, as the implant needs to be big enough to hold the load it will be subject to, and small enough not to damage the nerve.
It is also very important that the implants are placed in the right position from the beginning because once they have bonded with the bone, they are “welded” together and extracting the implant would mean a great loss of bone material in the jaw, which would complicate the rehabilitation and the results would never be the same.