Angst PDM, et al. - Researchers conducted a two-year randomized clinical trial to assess supportive periodontal therapy (SPT) composed of oral prophylaxis with oral hygiene instructions as sole intervention (test) or combined with subgingival instrumentation removing/disrupting the subgingival biofilm (control). Sixty-two patients treated with periodontitis were randomly assigned to receive either test or control treatment every 3 months over 2 years. Periodontal probing depth, bleeding on probing and clinical attachment loss were included examination in this analysis. During 2 years of SPT, oral prophylaxis with oral hygiene instructions alone or in conjunction with subgingival instrumentation could retain the earlier acquired periodontal condition to a similar extent.