Statistical analysis
Data were collected and added to a spreadsheet (Microsoft Excel, Microsoft Corporation, Redmond, Washington, USA). Statistical analysis was performed with a statistical analysis software (SAS 9.4, SAS Corp., Cary NC. USA). Descriptive summary statistics was obtained on the implant level as well on the patient level.On the patient level intragroup comparisons for the medians of the groups were performed by Wilcoxon-signed-rank test and the intergroup comparisons of the two groups were based on the Wilcoxon-Mann–Whitney test. Hodges-Lehmann 95%-confidence estimations are applied for the medians or for the difference of the medians.If the normality assumption was holding, F-tests were applied and 95%-confidence intervals for the means or differences of the means were determined.Nominal data of the two groups were compared on the patient level with the chi-squares test with exact derivations of the p-values.For the implant level mixed linear models were applied for the comparisons because of the dependence of the data within a patient.The level of significance was set at 5%. No correction of the multiple testing is applied.For the analyses of further impact factors we applied linear models for the patient level data and linear mixed models for the implant level data.