Sample size calculation and randomization Power analysis prior to the start of the study was difficult since no previous randomized controlled trials on this study product were available. The sample size was determined. Pocket probing depth was taken into account, with an expected difference of 0.82mm and a standard deviation of 0.61mm. It was calculated that 10 patients were needed in each group to provide 80% power with an alpha of 0.05 . Despite this low number and taking into consideration studies comparing the adjunctive effect of antibiotics to scaling and rootplaning, it was decided to include 24 patients in each group.