Functional dentistry views the oral cavity as an integral part of overall body health rather than an isolated anatomical system. It implies identifying and eliminating the causative agents of oral diseases, including oral microbiome dysbiosis, nutrition, inflammation, airway function, sleep, stress, and other aspects of patients' lifestyles. This review article provides scientific evidence supporting principles of functional dentistry. Scientific studies prove strong connections between periodontal disease and various systemic diseases. Oral microbiome research shows the importance of microbial balance for both oral and systemic health. Modern approaches to cariology, personalised risk assessment, and prevention-oriented medicine correspond to the principles of functional dentistry.