 Statistical analysis Sample size calculation is based on an observed standard deviation for CAL-V gain 1.6 mm in a study comparing regenerative therapy with and without antibiotics. To detect a mean difference of 1.0 mm with a test power of 80 and a type 1 error alpha 0.05 a minimal sample size of 84 patients has to be recruited, 42 for each group. Thus, it is decided to recruit a total of 90 patients. 