“…From 1982 to 1998, a total of 2,564 patients were treated for moderate‐to‐advanced periodontitis in the Department of Periodontology, Christian‐Albrechts‐University of Kiel, Germany. Three hundred ten patients, who received maintenance therapy for ≥10 years with ≥1 visit/year after non‐surgical/surgical active periodontal therapy (APT), presenting bone loss of ≥50% at ≥2 teeth, annual pocket probing depth (PD) documentation, and complete conventional radiography documentation at baseline (T0), at the end of the APT (T1), and at the last documented visit of maintenance therapy (T2), qualified for participation in the study 14 . Two hundred thirty‐eight patients had at least one first or second molar treated with OFS during APT (in total 939 molars).…”