This study describes size of constituent deciduous tooth crown components (enamel, dentine, and pulp) to address the manner in which males characteristically have larger teeth than females, and the observation that teeth of American blacks are larger than those of American whites. Measurements were collected (n = 333 individuals) from bitewing radiographs using computer-aided image analysis. Tissue thicknesses (enamel, dentine, pulp) were measured at the crown's mesial and distal heights of contour. Deciduous mesiodistal molar crown length is composed of about 1/7 enamel, 1/3 dentine, and 1/2 pulp. Details differ by tooth type, but males typically have significantly larger dentine and pulp dimensions than females; there is no sexual dimorphism in marginal enamel thickness. Males scale isometrically with females for all variables tested here. Blacks significantly exceed whites in size of all tissues, but tissue types scale isometrically with blacks and whites with one exception: enamel thickness is disproportionately thick in blacks. While the absolute difference is small (5.56 mm of enamel in blacks summed over all four deciduous molar tooth types vs. 5.04 mm in whites), the statistical difference is considerable (P < 0.001). Aside from enamel, crown size in blacks is increased proportionately vis-à-vis whites. Principal components analysis confirmed these univariate relationships and emphasizes the statistical independence of crown component thicknesses, which is in keeping with the sequential growth and separate embryonic origins of the tissues contributing to a tooth crown. Results direct attention to the rates of enamel and dentine deposition (of which little is known), since the literature suggests that blacks (with larger crowns and thicker enamel) spend less time in tooth formation than whites.
The purpose of this tooth-size study was to compare the crown index—the ratio of buccolingal to mesiodistal crown size—in the primary teeth of contemporary American blacks and whites. Maximum MD and BL drown dimensions were obtained with sliding calipers from dental casts of children attending the graduate pedodontic and orthodontic clinics at the University of Tennessee, Memphis (n = 226). The crown index (BL/MD times 100) was calculated for all 10 tooth types (left and right sides were averaged prior to calculation). Only the maxillary first molar exhibited a significant sex difference (girls have a higher crown index). In contrast, 9 of the 10 tooth types have signficantly higher crown indices in blacks than whites. Analysis of the MD and BL crown diameters reveals that the race differencs are due exclusively to differences in mesiodistal crown lengths; the buccolingual crown breadths do not differ between these two races. Consequently, the crown indices are higher in blacks because of their larger MD dimensions. Differences in the indices conform to prior findings that American blacks have larger tooth crowns than whites in both the primary and permanent dentitions, and this study shows that the differences are due to the MD not the BL crown axis. Study of the crown components will shed light on how the crown shapes differ between these two races.
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