Chronic oral infections, which are widespread and involve ongoing inflammation, may contribute to the development of systemic diseases. This study explored the potential role of long-standing oral conditions as risk factors for various chronic systemic illnesses, seropositive rheumatoid arthritis, including diabetes mellitus, Crohn’s disease, ulcerative colitis, and connective tissue diseases, as well as for severe mental disorders such as psychosis and other major psychiatric conditions. This cohort study included 68,273 adults aged 29 and older who visited Helsinki City Health Services for dental care at least once between 2001 and 2002. Participants’ records were linked with national registries, including mortality data from Statistics Finland, cancer diagnoses from the Finnish Cancer Registry, and medication reimbursement information from the Finnish Social Insurance Institution, with follow-up continuing until death or the end of 2013. Chronic disease outcomes were identified through the initiation of medications eligible for special reimbursement, indicating partial or full coverage of treatment costs. The diseases examined were diabetes mellitus, seropositive rheumatoid arthritis, connective tissue disorders, Crohn’s disease, ulcerative colitis and severe psychiatric disorders. The average follow-up period was 9.8 years. At baseline, approximately 25% of participants had periodontitis, 17% had dental caries, over 70% had apical periodontitis, and 9% had fewer than 24 teeth. Among the chronic systemic conditions studied, only diabetes showed a significant association with oral health indicators. Individuals with 24–27 teeth had a higher incidence rate ratio (IRR) of diabetes (1.21; 95% CI: 1.09–1.33) compared with those having 28 or more teeth, while those with 23 teeth or fewer had an IRR of 1.40 (95% CI: 1.22–1.60). Additionally, the presence of periodontitis (IRR 1.10, 95% CI 1.01–1.20), dental caries (IRR 1.12, 95% CI 1.01–1.23), and apical periodontitis (IRR 1.16, 95% CI 1.04–1.30) was linked to an increased risk of developing diabetes. Findings from our 10-year epidemiological follow-up indicate a link between diabetes and chronic oral diseases, highlighting the importance of coordinated care among healthcare professionals managing these patients.
