Economic impact on tooth emergence.

As shown in nearly 10,000 Negro and White boys and girls between 4.5 and 16.5 years of age, poverty-level children (with an income-toneeds ratio of 1.0) tend to be delayed in permanent tooth emergence as compared with those approximating median per-capita income. For boys, a per-capita income difference of $2200 was associated with a 0.15 standard deviation difference in emergence timing of 28 permanent teeth. The effect of socio-economic differences on the emergence timing of the permanent teeth constitutes a fundamental and still-unresolved problem in human dental development. It is relevant, moreover, to population comparisons (where economic differences are so often considerable), and in the analysis of human skeletal remains, where current tooth emergence standards may not be fully applicable. Quantitative information on the economic effect is scant, however, since few studies of tooth emergence have been specifically designed to resolve the fundamental question (cf. Fess, ’65; Garn and Russell, ’71). The present investigation, therefore, provides new tooth emergence information on a very sizable sample of subjects (N = 9656), separately for youngsters of European and largely-African derivation, and in conjunction with individual data on family income and family composition. In this tooth emergence study we have made use of precoded presence-absence dental data on 5788 White children (2967 boys and 2821 girls) and 3868 Black or American Negro children and adolescents (1847 boys and 2021 girls). The prime dental data were collected in the course of the ten-State Nutrition Survey of 19681970, and represent the eight states where exact birthdate information was reported and recorded (cf. Garn, Nagy and Sandusky, ’72; Garn, Sandusky, Nagy and McCann, ’72a; Garn, Wertheimer, Sandusky and McCann, ’72b; Garn, Sandusky, Nagy and Trowbridge, ’73a; Garn, Sandusky, Rosen and Trowbridge, ’73b). These states include Massachusetts, New York (including New York City), Michigan, Kentucky, West Virginia, South Carolina,California and Washington. The census designations “White” and “Black” were used for subject identification. As ascertained from the final corrected computer listings, the actual age range encompassed was 4.50 through 16.49 years, as computed from birthdate and date of examination. For each individual in the survey, family income, family size and age of individuals in the family were together calculated to provide an index of income relative to needs, so calculated that an index of 1.0 represents the poverty level (Orshansky, ’65, ’68; Ten-State Nutrition Survey, ’72). As described in the published report on the Ten-State Survey, “Ratios of less than 1.0 can . . . be described as ‘below poverty’; ratios greater than 1.0, as ‘above poverty,’ A family with a P.I.R. of 1.0 is living at the poverty line.” For the present study, two income-needs groupings were selected for comparison, one grouping with income-needs ratios up to 1.49 (and straddling the poverty line of 1.0) and a second income-needs grouping ranging from 2.25 upward (and approximating the median income level for 1968). We have separately calculated the percapita incomes for the two groupings used. The median per-capita income for the lower or poverty-level grouping approximated $720 per capita, while the higher income grouping had a median per-capita 233 AM. J. P H Y S . ANTHROP., 39: 233-238 234 GARN, NAGY, SANDUSKY A N D TROWBRIDGE income of $2920. These median values necessarily differ slightly from age to age and state to state, even though the cutoff values were consistent as given above. The per-capita income difference between the lower and higher income groupings was $2200 for Whites and somewhat less for Blacks. Recoding the presence-absence data for 28 individual teeth, I1 through M2, so as to count extracted or replaced permanent teeth as “present,” tooth emergence information was computer calculated, and initially analyzed state by state to detect and delete possible irregularities of coding or punching. Then the data for all eight states were combined, and analyzed by sex, by race, and by tooth, for each of the two economic groupings, using the publication of Klein, Palmer and yramer (‘37) as an inspectional guide, in data editing throughout. For the purposes of this study the measure of central tendency calculated was M , corresponding to the mean in a Gaussian distribution, as described previously by us (Garn et al., ’72a,b). Differences in emergence timing between the two income groupings were then calculated as d (difference in years) thus minimizing any bias resulting from choice of a particular algorithm. The direction of the differences (d) was tested by a simple sign test, against chance expectancy, to determine whether the higher income grouping was earlier (i.e., advanced) in tooth emergence for each of the sex-race comparisons. Further, the magnitude of the differences in tooth emergence (d ) was expressed as Z-scores or standard deviation units, using values of U , calculated from the total sample, as described in Abramowitz and Stegun (’64). Differences in Zscores were based upon values of u appropriate for sex, race and tooth, as set forth in table 1. Analyzing the income-groupings, then, for possible differences in tooth emergence timing, as reflected by differing values of M, permanent tooth emergence (11-M2) tends to be systematically delayed in the boys of lower income-needs ratios or lower per-capita incomes. This economic delay in tooth emergence is demonstrated first for White boys where 10 out of 14 combined-side tooth pairings are delayed or later in those in the lower or “poverty level” grouping. It is again demonstrated, separately, for Black or American Negro boys, where 11 out of 14 teeth are delayed