Sample size
The calculation was based on the BOP index of Slawik’s study, and its mean values were 76.23 ± 9.11 and 25.8 ± 72.12 for the test and control groups at day 14, respectively. The sample size of the mentioned indicator, with 95% confidence level and 90% test power for two test ranges, was estimated as equal to 30 participants (15 in each experimental and control group) using the formula of comparison between means in G-power software. It should be noted that considering the dropout rate of 40%, the final sample volume has been increased to forty-two (twenty-one in each group).