1. A mould or impression used to record the relationship of a tooth or teeth to one another or to a cast.
2. The formula expressing the ratio of one measurable value to another. An index may be defined as a numerical value describing the relative status of a population on a graduated scale with definite upper and lower limits designed to permit and facilitate comparison with other populations classified by the same criteria. Indices are used in health service research, epidemiological surveys, clinical trials, and also to diagnose disease and monitor the progress of treatment in individual patients. An index may be classified as reversible or irreversible, based on the direction in which its scores can fluctuate. It may be full mouth or partial mouth, depending on the area of the mouth examined. An index may assess only the presence or absence of the variable or it may assess the severity of the variable; it may relate the clinical finding to treatment need. A number of indices have been developed for use in epidemiology and clinical dental practice which include the calculus surface index, Community Periodontal Index of Treatment Needs, DEF index, DMF and dmf indices, extent and severity index, functioning teeth index, gingival bleeding index, gingival index, Greene–Vermillion oral hygiene and deposit index, index of complexity outcome and need (ICON), index of orthodontic treatment need (IOTN), papillary marginal attached (PMA) index, peer assessment rating (PAR) index, periodontal disease index, plaque index, and tissue health index.
Young W. O., Striffler D. F. The dentist, his practice and his community. Philadelphia, Saunders, 2nd edition, 1989.