Diederik Hentenaar

115 Phosphoric acid in surgical peri-implantitis treatment treatment allocation. Peri-implant pocket depth was measured at four sites per implant (mesial, buccal, distal and lingual) using a pressure sensitive probe (KerrHawe Click Probe, Bioggo, Switzerland) (probe force of 0.25 N). Bleeding and suppuration were scored up to 30s after pocket probing. Microbiological peri-implant sulcus samples were collected from each implant with peri-implantitis using 4 sterile paperpoints per implant. Paperpoints were collected in a vial containing RTF and were analyzed in the same manner as the intra-operative samples. Outcome variables were total anaerobic bacterial load and the presence and numbers of the periodontal pathogens Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, Tannerella forsythia, Fusobacterium nucleatum, Parvimonas micra and Campylobacter rectus . Randomization Fourteen notes with the word ‘phosphoric acid’ and 14 notes with the word ‘saline’ were put into 28 identical, sequentially numbered, non-transparent envelopes according to a randomization list generated by a computer program. The envelopes were irreversibly sealed. During the surgical procedure, after flap deflection and mechanical cleansing, the surgeon temporarily left the operating room. The surgical assistant opened an envelope and prepared the materials as needed according to the information on the note. A third person (YDW) performed the decontamination procedure according to group allocation. The materials were removed and the surgeon continued the surgical procedure. The researcher (performing the clinical measurements, DH) was blind to treatment allocation and did not have access to the randomization code until the end of the research period. Statistical methods Sample size Sample size was based on the microbiological data from a previous study evaluating the effect of implant surface decontamination with a chlorhexidine-solution versus a placebo-solution (De Waal et al. 2013). The decontaminating effect of phosphoric acid was expected to be similar to the decontaminating effect of chlorhexidine (reduction in log-transformed mean anaerobic bacterial load = 4.21 (chlorhexidine group) versus 2.77 (placebo group), SD = 2.12). Assuming a two-sided two sample t- test with a significance level (α) of 0.05 and a power (β) of 80% required a sample size of 34 implants. A 20% compensation for dropouts was taken into account (34/0.8 = 42.5 implants). Based on a previous study (De Waal et al. 2013) it was expected that not all baseline microbiological samples would yield a detectable number of cultivable bacteria (De Waal et al. 2013, 19 out of 79 = 24% of samples showed no bacterial growth). Because ‘negative’ samples cannot be used to determine a decontaminating effect, the sample size was 5