The present study used a novel approach to assess the relationship between untreated caries lesions and defective and non-defective dental restorations and the incidence of gingival inflammation and the progression of chronic inflammatory periodontal diseases at the approximal surfaces of posterior teeth and at the adjacent surface of the neighboring tooth in adolescents over a period of 3 years. Two hundred-twenty-seven (227) 13-year-old schoolchildren were examined clinically and radiographically at baseline and annually at three subsequent occasions. At each site the alveolar bone height and presence of gingival bleeding were assessed. Incipient caries lesions, manifest caries, and defective and non-defective restorations were identified at the same site and also at the adjacent approximal tooth surface at all examinations, both clinically and radiographically. The data were analyzed by the multi-level logistic regression and variance components analyses. On average, 32, 8.5, 7, and 10% of the sites, respectively, were diagnosed as having incipient caries, manifest caries, and defective and non-defective restorations. There was a significant association between the presence of untreated manifest caries lesions, non-defective and defective dental restorations, and the progression of periodontal support loss. Also there was an association between presence of defective restorations and manifest caries and the incidence of gingival inflammation. Consistently, factors detected at the involved site and at the adjacent site had significant effects. The present study indicates that untreated cavities and dental restorations are predisposing factors with a significant negative effect on periodontal health in adolescents.(ABSTRACT TRUNCATED AT 250 WORDS)