The Relative Sexual Dimorphism of Human Incisor Crown and Root Dimensions

Abstract

Teeth are unusual structures in that their dimensions are sexually dimorphic even though they form early in life, several years before steroid-mediated adolescence. These size differences make teeth attractive as indicators of a specimen’s sex. Alternatively, the magnitude of sexual dimorphism in humans is low, so there is considerable overlap in sizes between the two sexes. Prior studies suggest that tooth root dimensions are more dimorphic than crown dimensions, so roots would be more useful for sex determination. To explore this, we measured the four incisor tooth types from standardized periapical radiographs in a sample (n = 148) of living American white adolescents. Root lengths are somewhat more dimorphic than crown sizes in this sample (ca. 6% vs. 2%), and this translates into somewhat higher discriminatory power. The hindrance, however, is that all crown and root sizes are positively intercorrelated, so there is effectively just one dentition-wide axis of “tooth size” variation. Statistically, at least for these incisor tooth types, there is no added discriminatory power in the crown sizes once root dimensions have been accounted for, though the addition of data from other tooth types might improve discrimination somewhat.