Periodontitis is treated by regularly clearance of the disease-causing biofilm through domestic care and dental measures (Petersilka et al., 2002, Herrera et al., 2008). Healthy gums have intact papillae occluding the interdental area. Successful brushing cleans these areas; the prophylaxis of gingivitis for such patients does therefore not require special aids. In contrast, initial attachment loss as a result of inflammation or restorative therapy leads to additional cleaning needs, since the normal brush is not able to clean interdental areas as successful as vestibular and oral surfaces (Dörfer and Staehle, 2010).

It can be said that interdental brushes are the most effective tools for cleaning interdental spaces (Salzer et al., 2015). Compared with a toothbrush, they are the only tool showing better results of plaque removal and reduction of gingivitis (Slot et al., 2008). Therefore their use should not be restricted to older people with already reduced interdental papillae. A big advantage is that interdental brushes are generally easy to use. If brush sizes are chosen correctly, insertion and multiple forward and backward movement is sufficient to obtain com- plete cleaning of the interproximal surfaces. Additional cleaning by other means such as dental floss is not always necessary because interdental brushes clean approximal and subgingival surfaces sufficiently, providing the size was chosen correctly (Dörfer and Staehle, 2010).

Due to the above mentioned coherences and associations, this study includes the hypothesis that patients with periodontitis would benefit from the instruction and motivation of interdental brushes within the active periodontitis therapy in comparison to a periodontitis therapy without the instructed domestic interdental hygiene by a stronger reduction of clinical inflammatory characteristics (Salzer et al., 2015). The corresponding Zero-Hypothesis says that no difference would be found between both groups.

Inclusion Criteria:

• Generalized chronic periodontitis (CP)
• Generalized aggressive periodontitis (AgP)
• Availability for non-surgical periodontal therapy and reevaluation after 3±1 months.
• Moderate to advanced severity of periodontitis (≥30% of the sites with attachment loss ≥3mm)
• Age: 18 - 70 years
• ≥16 scorable teeth, without root caries

Exclusion Criteria:

• Localized chronic or aggressive periodontitis (<30% diseased teeth of all teeth)
• Smoking
• Tumour(s) of the soft or hard tissues of the oral cavity.
• Systematic disease, which include specific conditions to treat (e.g. prophylaxis of endocarditic)
• Women who are aware of being pregnant or who are breastfeeding.
• Forms of acute necrotizing ulcerating periodontitis