One hundred and ten patients were invited for follow-up evaluation. All patients were treated in the period from 10/2008 to 02/2015 in the Clinic of Oral and Maxillofacial Surgery, University Medical Center Mainz. Inclusion criteria were as follows: implant placement of a NobelActive implant, study subjects over 18 years old, residual bone dimension in the edentulous region of at least 5 mm in height and 4 mm in width, placement torque of at least 35 Ncm, non-smokers, and a follow-up period of least 1 year after implant placement. Exclusion criterion was treatment with bisphosphonates.

From a total of 110 invited patients, 98 patients showed up for a follow-up evaluation of the clinical and radiological status of the implants and fulfilled the abovementioned criteria. Twelve patients were dropped out because of sudden death (n = 1), moved to another place (n = 4) and were incompliant and did not appear for the follow-up (n = 7). The rest 98 patients included into the study were stratified into different groups according to risk factors (RFs) (local, systematic, both of them, or without risk factor), implant region, implant diameter, implant length, time of implant placement, and time of implant restoration.

Systematic risk factors included poorly controlled diabetes (HbA1c > 7%), irradiation (range; 58–64 Gy), chemotherapy (“EURO-E.W.I.N.G.99”—consisted of vincristin, ifosfamid, doxorubicin, and etoposid in one patient after resection of a sarcoma in the upper jaw), long-term therapy with corticosteroids (≥ 7.5 mg of prednisone equivalent per day during at least 90 days consecutive) [17, 18], and presence of Marfan syndrome. Local risk factors included history of severe [19, 20] periodontitis (clinical attachment loss > 5 mm)—which was not active at the time of implant placement—unsuccessful endodontic treatment with periapical pathology, implant placement in cases with moderate or severe bone defects (> 4 mm need for augmentation according to the Cologne Classification of alveolar ridge defects [21]), and replacement after removal of a previous implant (Table 1). Other co-existent diseases that do not influence the implant survival were not considered systemic risk factors.