Dentistry and internal medicine: from the focal infection theory to the periodontal medicine concept

During past decades the relationship between dentistry and internal medicine and especiallythe concept of the so-called focal infection theory have long been matter of debate. The pathogenesis offocal diseases has been classically attributed to dental pulp pathologies and periapical infections.Nonetheless, in recent years, their role is being dismissed while increasing interest is being devoted tothe possible associations between periodontal infection and systemic diseases. In fact, periodontalpathogens and their products, as well as inflammatory mediators produced in periodontal tissues,might enter the bloodstream, causing systemic effects and/or contributing to systemic diseases.On the basis of this mechanism, chronic periodontitis has been suggested as a risk factor forcardiovascular diseases associated with atherosclerosis, bacterial endocarditis, diabetes mellitus,respiratory disease, preterm delivery, rheumatoid arthritis, and, recently, osteoporosis, pancreaticcancer, metabolic syndrome, renal diseases and neurodegenerative diseases such as Alzheimer'sdisease. Various hypotheses, including common susceptibility, systemic inflammation, direct bacterialinfection and cross-reactivity, or molecular mimicry, between bacterial antigens and self-antigens,have been postulated to explain these relationships. In this scenario, the association of periodontaldisease with systemic diseases has set the stage for introducing the concept of periodontal medicine.This narrative review summarizes the evolution of focal infection theory up to the currentpathophysiology of periodontal disease, and presents an update on the relationships between chronicperiodontitis and systemic diseases