In accordance with the WMA Declaration of Helsinki—Ethical Principles for Medical Research Involving Human Subjects, approval was given by the local ethics committee of the Christian-Albrechts-University in Kiel (AZ 132/10). All patients gave informed written consent to participate.

A total of 201 sinus floor elevation procedures, which were performed from 2005 to 2006 in the Department of Oral and Maxillofacial Surgery of the University Hospital of Kiel, were primarily included in this retrospective cohort study. Within this cohort, 41 perforations (20.4%) of the Schneiderian membrane in 33 patients (21 female, 12 male) occurred. One patient was deceased, and one patient did not engage in the follow-up offered by the department. After exclusion of these two patients, a total of 31 patients aged 60.86 (± 11.21) years with 39 perforations were available to participate in regular recall examinations with an average observation time of 2.69 years (± 2.04 years). According to this study group, 32 patients with 40 sinus lift procedures without perforations aged 58.76 years (± 9.43) were randomized from the cohort to represent the control group (average observation time 2.14 years ± 1.85 years). Patients were recruited from the established recall system in the department. Requirements of inclusion were engagement in at least three follow-up visits after dental implantation and receiving dental implants in the department, if a two-stage procedure was performed. The inclusion rate of patients in the control group was 33.28%. In total, 56.16% of patients (54 patients) within the control group had not completed the follow-up visits for various reasons (relocation, impairment because of age, follow-up performed elsewhere) and therefore were excluded. Sixteen patients received implants in other private practices (16.64%), and 2 patients were deceased.

The manufacturer and position of implants were previously extracted from surgical reports in the medical record, as were in-house treated implant failures and consecutive explanation procedures. Vertical bone augmentation was additionally classified dependent on donor site (none/linea obliqua/iliac crest/scapula).