Biology Reference
In-Depth Information
TABLE 10.1 Standard Dental Metric Measurements and Crown Indices after
Hillson (1996)
and
Kieser
(1990)
Metric/Index
Measurement
Mesiodistal (length)
Maximum crown diameter in the M-D direction. To be taken parallel to the buccal/
labial surfaces.
Buccolingual (breadth)
Maximum crown diameter in the B-L direction. To be taken parallel to the mesial/
distal surfaces.
Crown module
(mesiodistal diameter
buccolingual diameter)/2
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Robustness index
mesiodistal diameter
buccolingual diameter
Summary tooth size
(summed robustness indices for all tooth classes)/(# of tooth classes)
the crown index is the buccolingual length divided by the mesiodistal length, multiplied by
100. Teeth that are wider than they are long have a value above 100 whereas teeth that are
longer than they are wide have an index below 100. Other commonly used indices are the
crown module, which gives an average of the size of a crown within a given tooth class;
the robustness index, which is essentially the area of the crown; and the summary tooth
size, which calculates the overall size of the dentition given the tooth classes included. A
thorough reference on dental metrics that includes data to explore is Human Adult Odontomet-
rics (
Kieser, 1990
). Within this volume, Kieser has compiled published mean and standard
deviation data for mesiodistal and buccolingual measurements on populations worldwide.
As mentioned above, humans have characteristic tooth shapes that are useful in sepa-
rating them from other species. Indeed, these same basic measurements are useful in discrim-
inating into broad populations as well. Populations across the globe show differences in
crown sizes, with Aboriginal Australians having the largest teeth overall and Western
Eurasians having some of the smallest. Tooth shape, as measured by the crown index, also
differs among human populations, with Polynesian and Western Eurasian groups having
teeth with narrower mesiodistal widths than their Native American and Northeast Asian
counterparts (
Hanihara and Ishida, 2005
).
Biological sex assessment from the teeth relies on the general trend of males having larger
teeth than females (within populations). As with other primates, the canine remains the most
dimorphic tooth in the human dentition. Just as adult bones are more sexually dimorphic
than juvenile bones, permanent teeth are more dimorphic than are the primary teeth and
so it follows that sex assessment from permanent teeth is more reliable than that from their
primary predecessors. DeVito and Saunders (1990) achieved sex estimation accuracy rates of
75
e
90% from the deciduous tooth size, whereas Hassett (2011) achieved rates of 94% for sex
discrimination from the adult canine dimensions.
It is important to note that standards for sexual differences in tooth size are subject to the
same issues of overlapping distribution between the sexes as skeletal measurements. There is
no clear cutoff for identifying male versus female dentition. While the trend exists for male
teeth to be larger than female teeth, there are always exceptions to the rule as a part of the
normal range of human variation. Therefore, dental measures should be considered in addi-
tion to as many other characteristics as possible in order to ensure the highest accuracy in sex
