Diederik Hentenaar

59 Erythritol air-polishing in non-surgical peri-implantits treatment Sample size calculation The sample size calculation for the present study was based on the total number of patients required for a two-staged trial design, so that enough patients from the non-surgical part would be available for the surgical part. Literature on sample size and a power calculation of multilevel analyses shows that at least 50 patients should be included for there to be a relevant statistic difference, since a total amount of less than 50 will lead to biased estimates of the second-level standard errors (Maas & Hox, 2005). Scherbaum et al. (2009) pointed out the relationship of different levels in accordance to an adequate sample size and power. Translation of this relationship to our research protocol means a sample size (amount of patients) in combination with implants nested in patients. With a mean group size of 2 infected implants per patient and a minimum amount of 50 patients, it was estimated to detect a medium effect size with 80% power at a significance level of α=0.05. Since our study focused on clinical relevant effects, small effect sizes were less important and detection of medium effect sizes were supposed to be sufficient for our study. According to the non-surgical peri-implantitis literature at the time of the study design, we estimated a 20% success rate for our non-surgical patient treatment phase (Muthukuru, Zainvi, Esplugues, Flemmig, 2012). Therefore, it was assumed that 80% of the patients would need surgical follow-up. To compensate for patient withdrawal and losses to follow up (10%), a sample size of 80 patients (40 in the air-polishing and 40 in ultrasonic group) was used. This was an intentional slight overestimation in order to assure enough available participants for the surgical phase of the study. Randomization Randomization was performed using sealed envelopes which contained a code ranging from AA to CZ alongside with a note saying either ‘air-polishing’ or ‘ultrasonic therapy’. The dental hygienist performing the procedure opened the envelope, wrote down the code, read the note and performed the procedure. A decoding list saying which code belongs to which procedure was kept sealed until data analysis. This way, the investigator did not know which procedure was performed. Statistical analysis To analyse the difference in clinical and radiographical efficacy between both treatments, generalized linear mixed models (GLMMs) were used (IBM SPSS Statistical software, version 23.0. for Windows, Armonk, NY: IBM Corp). A three-level structure was chosen with patient implant and time as level 1, 2 and 3, respectively. The patient was considered unit of analysis, whereas the implant the unit of observation. First, the T3 clinical and radiographical outcomes were analysed while controlling for the 3