Abstract The present study evaluated the long-term effect of (i) meticulous self-performed, supragingival plaque control and (ii) the use of a triclosan/copolymer containing dentifrice in adult subjects susceptible to destructive periodontitis. 40 individuals were recruited into the trial. 3-5 years prior to the baseline examination, they had all been treated by nonsurgical means- for advanced periodontal disease. During the subsequent maintenance phase, all subjects had at different time intervals exhibited sites with recurrent periodontitis. At a baseline examination. 6 surfaces per tooth were examined regarding bleeding on probing, probing pocket depth, and probing attachment level. The deepest pocket site in each quadrant (i.e. 4 sites per subject) was selected and samples of the subgingival bacteria were taken. At baseline, all volunteers received detailed information on proper oral hygiene techniques. This information was repeated on an individual need basis during the course of the subsequent 36-months. No professional subgingival therapy was delivered between the baseline and the 36-month examinations. The subjects were randomly distributed into 2 equal groups of 20 individuals each, 1 test and 1 control group. The members of the test group were supplied with a fluoridated dentifrice containing triclosan/copolymer (Total®. Colgate), while the controls received a corresponding dentifrice but without triclosan/copolymer. The findings demonstrated that in subjects with advanced and recurrent periodontitis, carefully practiced supragingival plaque control had some effects on the subgingival microbiota, but also that this was insufficient to prevent disease progression. In a corresponding group of subjects, however, who used a triclosan/copolymer dentifrice, the subgingival microbiota was reduced in both quantitative and qualitative terms and recurrent periodontitis was almost entirely prevented.