This clinical study evaluated the effect of different oral hygiene protocols on the bacterial composition of dental plaque. After a 2-week period of using fluoride-free toothpaste, 30 participants followed three 1-week experimental protocols, each followed by 2-week fluoride-free washout periods in a randomized crossover examiner-blind controlled trial. The 1-week experimental protocols comprised the use of AmF/SnF2 toothpaste twice daily, after which participants either (1) rinsed with tap water, (2) did not rinse but only spat out the toothpaste, or (3) rinsed with an AmF/SnF2 mouthwash. In the fluoride-free washout periods, the participants brushed their teeth with fluoride-free toothpaste without further instructions. Six hours after the last brushing (8 rinsing) of each period, buccal plaque samples in the upper molar region were taken. The microbiota composition of the plaque samples was analyzed by checkerboard DNA: DNA hybridization. A statistically significant reduction was found in the total amount of DNA of the 39 major plaque species measured, and in the proportions of some acid-producing bacterial strains after the period having used the AmF/SnF2 toothpaste + AmF/SnF2 mouthrinsing. The results indicate that using the AmF/SnF2 toothpaste and rinse combination could result in plaque of lower cariogenicity. Copyright (C) 2009 S. Karger AG, Basel