Objectives: The aim of this study was to assess factors contributing to the long-term effect of periodontal treatment 10 yearsafter initiation of antiinfectious therapy. The main outcome variable of this analysis was tooth loss. Methods: 64 adultpatients were recruited for the study. Inclusion criteria were full-mouth radiographs from the beginning of therapy andcompletion of antiinfectious therapy. Clinical examinations including periodontal findings, Plaque (PCR) and Gingival (GBI)Index, samples for analysis of interleukin-1 polymorphism (IL-1), and a detailled questionary on smoking habits, dental care,social status, and nutrition were obtained by the same examiner (BP). Additionally periodontal conditions were surveyedaccording to the criteria of the Swiss Dental Association (Schweizerische Zahnärzte-Gesellschaft 1999). Medical files weresearched for initial diagnosis, documentation of tooth loss, regularity of maintenance and prognosis index (Checchi et al.2002). The statistical analysis was performed with SPSS using linear regression. Results: The following means of tooth lossper patient were observed: regular maintenance (yes / no): 0.46 / 3.44; IL-1 polymorphism (positive / negative): 2.04 / 0.88;initial diagnosis (moderate chronic / severe chronic or aggressive periodontitis): 0.44 / 2.15; prognosis (A or B / C): 1.54 /2.36; gender (male / female): 1.50 / 1.89; smoking (no / yes): 1.02 / 3.65. Linear regression revealed increased tooth lossfor irregular maintenance patients (p=0.024) and those exhibiting the interleukin-1-polymorphism (p=0.049). Conclusions: Somecriteria seem to interact with tooth loss whereas only regular maintenance and absence of the interleukin-1-polymorphism couldbe proven to be statistically significant preventive of tooth loss. Keywords: supportive periodontal therapy, long-term success after systematic periodontal therapy, tooth loss, periodontitis risk factors, interleukin-1 polymorphism