Thomas Kocher, Karoline Lösler, Christiane Pink, Hans Jörgen Grabe, Birte Holtfreter

• Aim To assess the impact of active (APT) and supportive periodontal therapy (SPT) on the change in probing depth (PD) and annual tooth loss in partially and fully compliant and drop‐out patients. Material and Methods Data of 280 periodontally treated partially and fully compliant (regular supportive visits, SPT duration 5.5 ± 4.5 years) and 55 drop‐out patients (SPT and drop‐out duration 8.3 ± 3.8 years, only drop‐out duration 5.3 ± 3.7 years) were recorded. PD data and the number of teeth present at the start of APT (T1) and at the start of SPT (T2) were taken from the patient files and evaluated at the time of the final examination (T3). Results Annual tooth loss during SPT was significantly higher (p < 0.001) in drop‐out patients than in partially and fully compliant patients (0.31 ± 0.50 vs. 0.19 ± 0.55, respectively). In partially and fully compliant and drop‐out patients, the mean PD (all available site data) decreased significantly between T1 (3.61 ± 0.82 vs. 3.70 ± 0.73 mm) and T2 (2.68 ± 0.40 vs. 2.76 ± 0.42 mm), while the values increased again slightly up to T3 (2.74 ± 0.41 vs. 2.99 ± 0.75 mm). Conclusions In partially and fully compliant patients, SPT had a positive impact on PD stability and medium‐term tooth preservation. In contrary to expectations, drop‐out patients, PD did not return to baseline values, although PD stability was not achieved.