Sample size calculation/Power analysis The calculation of patients to be treated (sample size) was based on a previous proof-of-concept single-centre RCT (Wohlfahrt et al. 2012) and the primary objective to detect a true mean difference of at least 2 mm between test and control treatment for radiographic defect fill after 6 months. With a level of significance of alpha = 0.05 in a two-sided hypothesis and a power of 90 %, the number of patients needed was 48. Assuming a dropout rate of about 30% the total number of patients required was 60.