Angst PDM, et al. - A 2 years randomized clinical trial was performed to assess supportive periodontal therapy (SPT) consisting of oral prophylaxis with oral hygiene instructions as sole intervention (test) or combined with subgingival instrumentation removing/disrupting the subgingival biofilm (control). Sixty-two treated periodontitis patients were randomly assigned to receive, every 3 months during 2 years, either test or control treatment. The distribution of sites gaining or losing attachment +/- 2mm was comparable between groups. In 2 years of SPT, oral prophylaxis with oral hygiene instructions alone or in combination with subgingival instrumentation was able to maintain the previously obtained periodontal condition to a comparable extent.