Objectives: Assessment of factors contributing to tooth loss 10 years after initiation of periodontal treatment. Methods: 93 adult patients were recruited for the study. Inclusion criteriawere full-mouth radiographs from initiation of therapy and completion ofantiinfective therapy. Clinical examinations including probing parameters,Plaque and Gingival Index, samples for interleukin-1 haplotype (IL-1) test,and a detailed questionnaire on e.g. smoking habits were obtained by thesame examiner. Periodontal conditions were surveyed according to thecriteria of the Swiss Dental Association. Medical files were searched forinitial diagnosis, frequent supportive periodontal therapy (SPT) andprognosis index. Results: The following means of tooth loss per patientwithin the 10 years of observation were observed: gender (male/female):1.5±3.5/ 1.7±3.9; smoking (no/yes): 1.1±1.8/ 3.1±6.5; prognosis (A/B,C):1.4±2.4/ 2.7±4.9; initial diagnosis (moderate/severe chronic, aggressiveperiodontitis): 0.6±1.4/ 2.0±4.2; regular maintenance (yes/no): 0.45±0,8/3.1±5.1; IL-1 (no/yes): 0.95±4.7/ 2.1±1.3. Stepwise linear regressionanalysis identified irregular SPT and IL-1 haplotype to be associated withan increased rate of tooth loss (pConclusions: some criteria seemto interact with tooth loss whereas only regular spt and absence of il-1haplotype could be proven to be statistically significant in prevention oftooth loss.