Robert L. Glass

The Veterans Administration Longitudinal Study of Oral Health and Disease: Methodology and Preliminary Findings

The purpose of the present study is to evaluate the distribution, determinants, changes and inter-relationships observed in oral health, oral disease and oral function from findings of periodic examinations performed at regular intervals in a population of male veterans in good health at the outset.

The prevalence of human dental caries and water-borne trace metals

Abstract Marked differences in the prevalence of dental caries have been observed in two isolated villages in Colombia, South America. These differences approximate those observed between areas of minimal and optimal fluoride ingestion, although each village has less than 0.1 ppm fluoride in the drinking water. Dietary histories reveal remarkedly similar dietary practices. Samples of drinking water were collected from these villages, and analyzed by emission spectroscopy for the concentrations of 21 trace elements. In the case of 13 elements, concentrations were at or below the threshold of detection or showed minimal variability. Concentrations of calcium, magnesium, molybdenum and vanadium were higher in the water samples from the village with the low caries prevalence, while concentrations of copper, iron and manganese were higher in the samples from the village with the higher prevalence. These differences were highly significant. The caries prevalence in the high caries village was typical of the country as a whole.

The appropriateness of analysis of variance to the statistical analyses of dental clinical trials

Abstract The extreme skewness and kurtosis of dental caries increments raise a question concerning the validity of analysis of variance for the statistical analysis of dental clinical trials. While it is acknowledged that moderate departures from normality do not strain the validity of parametric methods, the extent to which such departures from normality may be tolerated is not well known. In order to test the appropriateness of analysis of variance procedures in the statistical analysis of dental caries clinical trials, the increments in caries from clinical trials were simulated by computer for groups of varying size and number by random sampling from populations showing highly skewed distributions of new caries counts. Populations with both zero and nonzero true differences in the caries increments were sampled. Analysis of results of 320,000 simulated trials involving over 57 × 106 observations indicates that in spite of the extreme skewness and kurtosis of distributions of new caries counts, conclusions drawn from analysis of variance methods may be accepted with probabilities of Type I and II errors no greater than those predicted from normal distribution statistical theory. The evidence of the simulations suggests that analysis of variance and Dunnetts t-test, using the tabled critical values of F or t, may provide slightly conservative tests of significance. These results are in the same direction as predicted from the application of theoretical procedures and supply a justification for the extension of these theoretical procedures to distributions possessing the extreme skewness and kurtosis of caries count distributions, when the sample sizes and number of treatment groups are similar to those actually encountered in dental clinical trials.

Dental Caries and Soil Content of Trace Metals in two Colombian Villages

Notable differences in the prevalence of dental caries have been demonstrated between the children of the town of Heliconia, Colombia, and the nearby town of Don Matias (R. MEJIA, F. ESPINAL, H. VELEZ, and A. VELEZ, Bol Of Sanit Panam 66:50 1-507, 1969). The mean number of decayed, missing, and filled permanent teeth per child was 5.5 in Heliconia, and 13.9 in Don Matias; the latter figure is typical of this region of South America. Gross dietary factors and other factors known to influence dental caries, including fluoride ion consumption, do not account for the lower rate of caries in Heliconia (K. J. ROTHMAN, R. L. GLASS, F. ESPINAL, and H. VELEZ, J Public Health Dent, in press). Since it has often been hypothesized that trace metals in soil influence dental caries, presumably by a dietary effect, we examined samples of soil in Heliconia and Don Matias to determine whether the level of various trace metals in soil is associated with the caries dif-

DESIGN OF CLINICAL STUDIES OF DENTAL CARIES

The art and science of the evaluation of therapeutic agents have assumed complex significance as a result of the application of scientific principles to health practice. Changing attitudes toward health, increased funds available for health research, new emphasis on disease prevention, the growth of the pharmaceutical industry-all have contributed to growing emphasis on clinical trials, including the development and expansion of associated regulatory bodies.‘ Although the concept of evaluating drugs in humans is not new, the impetus for well-controlled trials probably dates back to the 1940’s and early successes with sulfonamides and penicillin. Similar advances have been evident in dentistry; the best illustrations are such established preventive procedures as topical fluoride applications and fluoridation. The research underlying these methods is the antithesis of the empiricism underlying the choice of drugs in the past, although some of these (for example, oil of cloves) are effective and still in use.3 The design of clinical trials and the appropriate analysis of the data from them owe much to the work of Fisher in the 1920’s and 30’s. Of particular significance is the recognition of the importance of randomization in experimental design as a result of Fisher’s work.4 Three regulatory bodies are noteworthy: the U.S. Public Health Service, the Food and Drug Administration, and the Council on Dental Therapeutics of the American Dental Association. A recent policy statement of the Surgeon General lists specific prerequisites for Public Health Service support of studies involving human subjects, requiring that such s t u d i e ~ : ~ 2

Caries Prevalence in Children from the United States

The National Center for Health Statistics (NCHS) estimates United States health status through studies of health resources, health interview surveys, and health examination surveys (HESs). Caries prevalence in US children has been estimated through a 1965 HES of 7,119 children. These children made up a highly stratified probability sample of the target population of 6to 11-year old children located in 40 sampling units throughout the US (KELLY and SCANLON, Decayed, Missing and Filled Teeth Among Children, HEW Publication No. 721003) . The mean counts of DMF teeth in this HES seemed low, and therefore, were plotted in the illustration along with corresponding means of age-specific DMF counts from five areas of known fluoride background. Tests of statistical significance were not carried out; they are inappropriate because of the absence of random sampling. DMF values from the 1965 HES are separated minimally from the values derived from two groups exposed to lifetime fluoridation in Newburgh and Grand Rapids (AST and FITZGERALD, JADA 65: 581-587, 1962; ARNOLD ET AL Public Health Rep 71: 652-658, 1956). Corresponding DMF values from the nonfluoride areas of Kingston, Muskegon, and metropolitan Boston (GLASS, unpublished) are appreciably higher and also are clustered together. It would be expected that estimates of caries prevalence for the entire US would be somewhere between the two groups of curves, because approximately half of the HES sampling units were fluoride areas (Fluoridation Census 1969, US Department of Health, Education and Wel-