Materials and methods Inclusion and exclusion Only implants that were lost due to mechanical failure or because of severe bone loss will be used. In the case of bone loss, an analysis will only be performed if sufficient osseointegration took place apical to the implant, at least about ¼ of the length of the implant. All these failed implants should be removed from a clinical point of view, but the extensive osseointegration purpose necessitates the clinical use of a trepanbur, a cylindrical bur to remove jaw bone. All patients will, prior to surgery, give informed consent to use their implants for further research, as well as the data from their clinical file.