Discriminatory Effectiveness of Crown Indexes—Tests Between American Blacks and Whites

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.

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