Relevance. In patients with comorbidities, the barrier resistance of periodontal tissues decreases due to oral homeostasis damage, which increases the severity of inflammatory periodontal diseases and needs the interaction of dentists and internists to develop common approaches to such patients' treatment and management.Aim. The study aimed to study the periodontal and oral hygiene indices and the oral fluid mineral composition in dental patients with comorbidity.Materials and methods. The study examined 63 dental patients with comorbidities: coronary artery disease, chronic gastritis, chronic nephritis, and chronic sinusitis. The Green-Vermillion oral hygiene index (OHI-S) detected the oral hygiene status, and the CPITN index of the WHO and the PMA index revealed the periodontal status. Electrothermal atomic absorption spectroscopy using QUANTUM.Z1 graphite furnace atomic absorption spectrometer determined the amount of calcium, magnesium, zinc and copper in the oral f luid.Results. Patients with coronary artery disease and chronic nephritis demonstrated a statistically significant decrease in oral hygiene associated with severe periodontal inflammation. Analysis of the oral fluid mineral composition showed that patients with coronary artery disease had decreased calcium, magnesium and zinc levels. The chronic nephritis patients had a copper and zinc decrease in the oral fluid. In patients with chronic gastritis, there was a lack of magnesium and copper in the oral fluid. The patients with chronic sinusitis showed a decrease in copper.Conclusions. Dental professionals should consider patient systemic diseases and oral fluid mineral composition at a dental appointment, during treatment and during preventive measures prescription.