The aim of this study was to determine the efficacy of rinses with slurries of a dentifrice containing triclosan (TCS), as compared with rinses with slurries from a control dentifrice, in controlling early subgingival biofilm formation. A double-blind, randomized and cross-over clinical trial was designed, and 26 dental students were included. In the first period, participants were randomized to rinse with a TCS slurry or a control slurry, in a 12 h interval, and to refrain from mechanical cleaning. A Plaque Free Zone Index was assessed at 24 h, 48 h, 72 h and 96 h. After a washout period of 10 days, the second experimental period was conducted, following the same protocol as the first period, except that the slurry groups were switched. Use of the TCS slurry resulted in a significantly higher percentage of plaque-free surfaces, both at 24 h and at 72 h (p < 0.01). In the of 48-72 h interval, the triclosan slurry showed a lower percentage of sites converted to a score of 2 (38.1% for the test versus 40% for the control product, p = 0.015). In conclusion, rinsing with slurries of dentifrice containing TCS retards the down growth of bacterial biofilms from the supra- to the subgingival environment.