Diederik Hentenaar

86 Chapter 4 to Lab Oral Diagnostics (Houten, the Netherlands) and analysed using real time-PCR (quantitative polymerase chain reaction - qPCR). Outcomes Primary outcome The change in the mean of 6 peri-implant sites (%) showing BoP was defined as the primary outcome. Secondary outcomes Peri-implant parameters SoP (%), Plq (%) and PPD (mm) and full mouth periodontal parameters BoP (%), SoP (%), Plq (%), PPD (mm) were defined as secondary clinical outcomes. The change in mean of 6 sites per implant and tooth was calculated. Mean marginal bone loss (mm) and the presence and levels of 8 classical periodontal bacterial species were other secondary outcomes. Success criteria The surgical implant therapy was considered successful at the 12 month evaluation when implant sites demonstrated: • PPD < 5mm • Max 1 out 6 sites BoP • No suppuration on probing • No progressive radiographic bone loss ≥ 0.5mm, compared to baseline study radiographs Sample size calculation The sample size calculation for the present study was based on the total number of patients required for the two-staged treatment design ( i.e., surgical therapy following non-surgical therapy in case of persisting peri-implantitis). A calculation was performed in such a way that a sufficient amount of patients from the non-surgical phase would be available for the surgical phase, taking into account a three-level mixed model structure. Additionally, the total number of patients was estimated from a sample size and power calculation for a three-level mixed model structure, with implants (level 1) nested in patients (level 2), which are analyzed over time (level 3). Literature on sample size and a power calculation of multilevel analyses has shown that at least 50 patients should be included for there to be a relevant statistic difference (Maas and Hox, 2005). Scherbaum and Ferreter (2009) pointed out the relationship of different levels in accordance to an adequate sample size and power (Scherbaum and Ferreter, 2009). Translation of this relationship to our research protocol means a sample size (amount of patients)