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estimation. Finally, population differences in the degree of tooth size dimorphism also exist,
making it important to find a suitable reference sample for comparison and evaluation
( Kieser, 1990; Hanihara and Ishida, 2005 ). See Moore [Chapter 4], this volume, for a more
detailed investigation of sex estimation from the dentition.
Nonmetric Dental Traits
Nonmetric dental traits are features of dental morphology that show variation in their
expression both within and between populations. One of the earliest published nonmetric
traits was the shovel-shaped incisor described by Hrdli
cka (1920) , who suggested a three-
grade system for describing expression of the trait. This trait presents as an incisor with
accessory ridges on both the mesiolingual and distolingual edges of the tooth, so that it looks
similar to a shovel. As Hillson (1996) mentions, just as metric traits present along
a continuum, so do nonmetric traits. However, due to difficulties in obtaining consistent
measurements, the continuum of nonmetric traits is often best assessed on a graded basis.
The most widely used set of trait assessment standards to document such traits was devel-
oped by the Arizona State University Dental Anthropology Laboratory. The Arizona State
University Dental Anthropology System (ASUDAS) consists of a series of plaques displaying
the various grades of each defined trait made from dental casts as well as a manuscript that
describes the interpretation and grading of such traits. The system describes the form of some
27 dental traits ( Turner et al., 1991 ).
One such trait is the famous Carabelli's trait. First described in 1842 by Georg Carabelli,
the trait ranges from a small groove or pit to a fully developed additional cusp. It appears on
the mesiolingual surface of the first maxillary molar and occasionally on the second maxil-
lary molar. As with other nonmetric dental traits, Carabelli's trait occurs on a continuum
from slight to marked expression. This is an excellent example of the need for an additional
scoring system to metric analysis as the form and nature of traits change with the degree of
expression. This transformation in the form of a trait due to degree of expression eschews
more traditional measuring techniques and therefore its classification is more amenable to
the stage-based scoring technique used in the ASUDAS.
Certain nonmetric traits have gained a solid foothold within biological anthropology as
characteristic of certain populations. For instance, the shovel-shaped incisor is commonly
associated with Asian and Native American populations and Carabelli's trait is often used
as evidence of European ancestry, and examples of these generalizations will be found in
most introductory biological anthropology textbooks. While these are rather accurate charac-
terizations due to the high prevalence of the individual traits in the given populations, as
a student of skeletal biology it is wise to keep in mind that no single trait defines a population.
In addition to seeking out further evidence for any assessment of the biological profile in the
dentition through metric analysis, it is also best to consider the spectrum of nonmetric traits.
Population affinity can be more confidently assessed using a suite of characteristics as
different populations express different combinations of traits. 2 Finally, it is always best
2 See DiGangi and Hefner (Chapter 5), this volume, for more information about population variation and
the shovel-shaped incisor trait and Cabana et al. (Chapter 16), this volume, for a discussion of genetic trait
distribution.
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