Forty-four volunteers, none of whom used tobacco products, were recruited and randomly allocated to either a test (n = 22) or placebo group (n = 22; Figure S1). Participants were asked to allow 2 lozenges per day to slowly melt in the mouth and to circulate the dissolved tablet contents around their mouths. One lozenge was taken in the morning and 1 in the evening for 12 weeks. The test lozenges contained L. reuteri (DSM 17938 and PTA 5289; 108 CFU per strain; BioGaia AB, Stockholm, Sweden), isomalt, hydrogenated palm oil, peppermint and menthol flavoring, peppermint oil, and sucralose (http://www.biogaia.com/product/biogaia-prodentis-oral-lozenges). The placebo lozenges were identical to the test lozenges in appearance, taste, and composition except the lactobacilli. Compliance was monitored as the percentage of lozenges consumed of the total assigned number. The remaining lozenges were counted when the containers were returned for monthly refills to assess this factor. Compliance was considered acceptable if ≤15% of the lozenges remained. Participants were asked to abstain from oral hygiene for 48 h and to not consume any food for at least 4 h before sampling. Participants were also instructed to not eat probiotic products throughout the study period.