The membranes applied included the native collagen membrane Geistlich Bio-Gide (Geistlich Pharma AG, Wolhusen, Switzerland) either alone or combined with one of the following membranes: Vicryl (Johnson & Johnson Medical GmbH, Norderstedt, Germany), Biovin Membran (OT Medical, Bremen, Germany), Parasorb Vlies (Resorba, Nuremberg, Germany), Gore-Tex Resolut (W.L. Gore & Associates, Flagstaff, USA), Kollagenresorb (RESORBA Medical GmbH, Nuremberg, Germany), Epi-Guide (DSM, Exton, USA), Gore Resolut Adapt Regenerative Membrane (W.L. Gore & Associates, Flagstaff, USA), Osseoguard (Biomet 3i, Munich, Germany), Ossix (Tel Aviv, Israel), Parasorb Resodont (RESORBA Medical GmbH, Nuremberg, Germany), Tefgen (Lifecore Biomedical, Chaska, USA), Tutodent (Tutogen, Neunkirchen, Germany), non-resorbable Gore-Tex membrane (GT, W.L. Gore & Associates, Flagstaff, USA), Osseoquest (W.L. Gore & Associates, Flagstaff, USA) and Inion GTR (Curasan, Kleinostheim, Germany). If a titanium mesh was used (Tiomesh, Dentaurum, Germany), the membranes were placed over the mesh.

Patient data files were analysed regarding personal patient information, implantation process and implantation outcome in terms of implant loss. Patient data included information about the sex, date of birth, the number and position of implants placed as well as the date of implantation and explantation or last control visit. Regarding the implantation procedure, the use of graft materials and membranes were documented.

Collected data were retrospectively analysed in terms of explantation rates to evaluate the survival between implants undergoing augmentation or not. Additional subgroup analysis included comparisons of different augmentation procedures, graft materials and membranes. In order to compare augmentation procedures, they were categorised into lateral augmentation, three-dimensional augmentation using a titanium mesh, bone splitting/bone spreading, use of autogenous bone blocks, internal sinus floor augmentation using the Osteotome technique and external sinus floor augmentation using a lateral window approach (one- and two-step procedure), bone condensing or combinations of these procedures. Bone splitting/spreading and bone condensing describe accompanying augmentation procedures to equalise the bone level with neighbouring sites.