Preterm delivery of low birthweight infants.

The concept that periodontal disease might influence systemic health is not new. Miller originally published his “focal infection theory” in 1891,1 suggesting that “microorganisms or their waste products obtain entrance of parts of the body adjacent to or remote from the mouth.” Miller and subsequent proponents of the focal infection theory2-4 blamed oral foci of infection for a number of regional and systemic diseases, ranging from tonsillitis and middle ear infections to pneumonia, tuberculosis, syphilis, osteomyelitis, endocarditis, meningitis and septicemia. Before the development of modern periodontal treatments, many teeth were extracted prophylactically because of the focal infection theory.3,4 Then, in 1952, an editorial in the Journal of the American Medical Association stated that “many patients with diseases caused by foci of infection have not been relieved of their symptoms by removal of the foci. Many patients with these same diseases have no evident focus of infection; also, foci of infection are as common in apparently healthy persons as those with disease.”5 The focal infection theory was not revisited for the next 50 years. However, recent progress in identification and characterization of periodontal pathogens, as well as elucidation of potential systemic mechanisms of action of bacterial products and inflammatory cytokines, have opened the way for a more realistic assessment of the systemic importance of periodontal disease. Epidemiological and microbiological–immunological studies have lent credence to the concept that periodontal disease may be a separate risk factor for cardiovascular disease, cerebrovascular disease and respiratory disease, as well as preterm delivery of low-birth-weight infants.6,7