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Discriminatory Effectiveness Of Crown Indexes—Tests Between American Blacks And Whites

Candice L. Foster, E. Harris
Published 2018 · Psychology

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Tooth crown shapes differ among human groups because the sizes and shapes of the constituent crown components differ. It was of interest to us whether there is patterned variation in crown indexes between sexes or among ethnic groups. The crown index—buccolingual width as a function of mesiodistal length—was analyzed here in terms of sex and race differences in a cohort of American black and white adolescents (n = 324) from the U.S. Mid-South. The mandibular canine is distinctive in exhibiting significant sexual dimorphism in crown shape, with females being broader in terms of mesiodistal length. Prior literature reports the crown indexes of several tooth types to be dimorphic, which does not occur here, showing that the extent of sexual dimorphism differs among groups. In contrast, we found that multiple crown indexes differ significantly between the samples of blacks and whites, with the largest differences in UC, UP1, and LM2. Of note, nature of the differences are tooth-specific, suggesting that divergence among groups at this microevolutionary level has shifted crown shapes along distinctive (rather than parallel) pathways. The optimum subset of crown indexes correctly allocates 67% of the specimens as to race; this percentage is not much better than chance, suggesting that crown indexes are of little forensic usefulness in discriminating among contemporary humans. Dental Anthropology 2009;22(3):85-92. osteologists, and craniometrists that emphasize shape rather than size differences (e.g., Wilder, 1920; Martin, 1928), though Albrecht et al. (1993) provide some cautionary notes against the uncritical use of ratios. The crown index (BL/MD times 100) has long been used as a measure of crown shape. Selma Thomsen (1955, p 4) states that, “This index was introduced by Retzius, a Swedish anatomist,” but she does not supply a citation. Anders Retzius (b. 1796 – d. 1860) is better known in dental circles as the person who described histological features of the enamel: “In ground section the enamel is marked by brown bands called the bands, striae, or incremental lines of Retzius” (Bhaskar, 1962, p 103). Application of the crown index evidently caught on quickly; de Terra reports it (Zahnbogenindex) without explanation (de Terra, 1905). The crown index expresses crown width (BL) as a function of length (MD), so a large index reflects a broad-short crown form, while a small index indicates a narrow-long form. The index is only an approximate measure of shape because tooth crowns are not essentially rectangular in form. The purpose of the present study is to explore the utility of using crown indexes of the permanent teeth to distinguish between males and females and, secondly, Correspondence to: Edward F. Harris, Department of Orthodontics, University of Tennessee, Memphis, TN 38163. E-mail:
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