Fortunately this occurs rarely and the success rate for dental implants is over 95%.  However failures are still a possibility and an understanding of this is a prerequisite for proceeding with your treatment.  Any potential problems specific to your implant treatment will have been anticipated and discussed with you before treatment starts.  Should an implant fail it is often possible to replace it at with a second implant at the same time as the first implant is removed.  It will of course be necessary to wait a further six months while the second new implant attaches to the bone.  It is not difficult to replace the failed implant at this time as it will be very loose and is easily removed.  It has been shown that alcohol and tobacco consumption can reduce the rate of success.  These habits also have an effect on the rate of healing and may increase the chances of post-operative infection.