The decline in dental caries in U.S. schoolchildren, first observed nationwide in 1979-1980, was confirmed further by a second national epidemiological survey completed in 1987. Mean DMFS scores in persons aged 5-17 years had decreased about 36% during the interval, and, in 1987, approximately 50% of children were caries-free in the permanent dentition. Children who had always been exposed to community water fluoridation had mean DMFS scores about 18% lower than those who had never lived in fluoridated communities. When some of the "background" effect of topical fluoride was controlled, this difference increased to 25%. The results suggest that water fluoridation has played a dominant role in the decline in caries and must continue to be a major prevention methodology.

Periodontal indices such as the PI, PDI and CPITN ignore a substantial amount of the information ordinarily available in epidemiologic studies of periodontal disease. The extent and severity index (ESI) is an attempt to preserve the maximum amount of information from a clinical examination consistent with the need to achieve a reasonable degree of data reduction. The ESI uses estimates of attachment level from probing measurements of 14 sites in one maxillary quadrant and 14 in the contralateral mandibular quadrant. The index is calculated to summarize jointly the extent and the average severity of disease within the group being studied. Application of this bi-variate statistic to a set of epidemiologic data was carried out to illustrate its use. This analysis suggested that disease extent and disease severity are not highly redundant measures and thus provide independently meaningful information. The ESI is a simple, reproducible method which appears to yield an informative description of the periodontal disease status of a population. Use of the index requires only minimal training of examiners. The index is intended to permit direct comparisons among epidemiologic studies of different populations and by different investigators.

Since the recognition of the potential of fluorides as caries preventatives, the interest of many dental epidemiologists has shifted from descriptive to experimental studies of oral disease, resulting in unprecedented advances in the control of caries and its sequelae. Judging from the proportion of effort in this direction, there has been a tendency to overlook the fact that the descriptive epidemiology of caries remains vague in several important, if undramatic, areas. Among these can be cited the equivocal explanations of differential caries experience between the sexes and among various racial groups, incomplete understanding of the relative magnitude of the genetic component in caries susceptibility, and a lack of careful documentation of attack patterns in specific teeth over time. Most of the existing body of information on the natural history of dental caries was developed some 20 years ago from the cumulative results of many cross-sectional, often non-comparable, observations of various population groups. Of the hundreds of such studies reported the most significant were probably those conducted by who utilized time-specific prevalence data to infer a very large amount of information about the influence of several variables, including duration of exposure, on patterns of caries incidence. These investigators have pointed out, however, that complete understanding of certain aspects of the epidemiology of caries requires longitudinal, rather than cross-sectional, studies of the same, stable population.2 4' 8 Information

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