Patients were scheduled to follow-ups at 6 months, 1-, 2-, 3-, 4-, and 5-year post-loading for the assessment of the study parameter (Fig. 1). Depending on the investigators’ standard post-operative protocol, follow-up appointments were scheduled slightly differently: One center skipped the control visits at 6 months. Additionally, due to the observational character of the study and the patients’ willingness, a flexible scheduling was necessary. Regular oral maintenance care (dental hygiene session) was performed individually for every patient during the entire study period. X-rays were done as usual in the individual centers and photographs were taken. The oral health status was measured by assessing the plaque index and sulcus bleeding index, if routinely performed in the practice. All but one center documented the indices leading to representative results. And the patients filled a questionnaire asking for their satisfaction regarding comfort, appearance, ability to chew, ability to taste, and general satisfaction with their restoration at each visit (PROMs) [18, 24, 25].

The primary outcome was to assess implant survival of the implants 5-year post-loading. Secondary outcomes were changes of the bone level over time, evaluation of peri-implant soft tissue, as well as the evaluation of patients’ related outcome measures.

Prior to study start, all examiners met for calibration of the parameters. Implant survival and complications were documented at each study visit. Changes in crestal bone levels (BLC) were assessed measuring the distance implant shoulder to first visible bone contact (DIB) at the mesial and distal site of an implant on available radiographs, either peri-apical radiographs or orthopantomograms (OPTGs). The radiographs were not standardized throughout the study centers. Non-digital radiographs were digitized by scanning (Epson Perfection V700 Photo). The radiographs were calibrated and analyzed in an image-processing software (ImageJ 1.50i; http://imagej.nih.gov/ij). BLC were calculated as difference between surgery and loading, as well as between loading and 1-, 3-, and 5-year post-loading. Due to the observational study character, radiographs could not be collected systematically and therefore were not available for all patients and time points. The evaluation of soft tissue parameters and patient-related outcome measures regarding functional and esthetic outcome of the dental restorations are described in Figs. 4 and 5 respectively. Adverse events were documented throughout the study.