12 Epidemiology : It ’ s Application in Periodontics

From immemorial time man has been interested in trying to cure and/or control of periodontal diseases. In view of the limitations of several theories (i.e., ‘Focal infection theory’, ‘Theory of contagion’ and ‘Germ theory of disease’), scientific thought began to search the other factors or causes in the etiology of periodontal diseases namely social, economic, genetic, environmental and behavioral factors. Thus, a newer concept (Multifactorial causation) of periodontal diseases has been evolved by investigators. Recently, evidence has also shed light on the relationship between systemic health and periodontal diseases, that is, possible adverse effects of periodontal disease on a wide range of organ systems (i.e., cardiovascular, endocrine, reproductive, respiratory). Hence, the application of epidemiology in the field of periodontics has utmost importance to measure prevalence, extent and severity of periodontal diseases, its relationship to other factors (age, oral hygiene, and nutrition), to assess the degree of association between periodontal diseases and systemic health and to improve treatment modalities for the prevention and control of periodontal diseases. The word ‘Epidemiology’ (Epiamong, demospeople, logosstudy) is derived from the term ‘epidemic’. ‘Epidemiology’ is defined as the study of the distribution and determinants of health related states or events in population and the application of this study for the prevention and control of health problems (Last, 1983). Epidemiology is more often concerned with the well being of society as a whole rather than the well being of individual. Three most important components of epidemiology are study of disease frequency (incidence/prevalence), study of disease distribution (i.e., age, sex, race) and (3) Study of determinants (causative/risk factor) of disease. Etiologic (causative) agent is defined as the living/nonliving substances or forces which may initiate or exaggerate the disease process by its excessive presence or relative lack. Risk factor is a subjective determinant of some disease processes (periodontitis, cancer) when true disease causing agent is not fully established. In epidemiologic study, three types of causal relationship are identified between different variables and manifestation of disease (Brownson, 1998) as they are shown in Fig. 1. Variable is a characteristic that helps to measure changes of disease processes varies from person to person. It may be dependent/ uncontrolled variable (i.e., age, genetics) or independent variable that can be controlled or manipulated (i.e., smoking). The presence of risk factor does not imply that always disease will occur and in its absence, disease will not occur. In a disease, they are additive/synergistic, observable/identifiable, can be modified or non-modifiable. The basic aims of epidemiology are: (1) to explain