Allocation/randomization of subjects
RECRUITMENT
The subjects were stratified into groups according to values higher or lower than the median of the Shannon index, an index of α‐diversity of the microflora, in the saliva collected at the time of recruitment. Subjects in the two stratified groups were then randomly allocated to the two study groups using a random number table prepared by Microsoft Excel to ensure an equal distribution of baseline oral bacterial diversity in the two groups. To avoid bias due to differences in groups, blinding was performed by researchers not involved in the evaluation. Therefore, the dentist and dental hygienist in charge of the evaluation were blinded to the grouping of the participants.The sample size required was calculated with reference to Teng et al. (