A perspective on periodontal diagnosis.

Periodontal diseases are best considered as the outcome of an imperfect host-parasite interaction. In most cases, diagnosis involves labelling certain clinical manifestations without a complete understanding of the causes of the disease. Therefore, treatment based on the "diagnosis" is not necessarily logical or effective. As the causes which underly the disease become more evident, the underlying mechanisms of disease can be used to refine our diagnostic methods. For example, deficiencies in host defenses, or the presence or increased proportions of certain bacterial pathogens may be indicative of imbalances in the normal host-parasite equilibrium. For a laboratory test to be reliably applied to the diagnosis of a clinical condition, it is essential that an absolute criterion of the clinical disease first be established. Then the sensitivity and the specificity of the test can be determined using appropriate experimental designs. The demonstration of a good correlation between a test outcome and a clinical condition is, of itself, insufficient grounds to use the test for diagnostic purposes.