Biology Reference
In-Depth Information
practice to combine information from the dentition with that available in the skeletal remains:
use every element of the skeleton that is available to you.
TOOTH DEVELOPMENT AND WEAR
Studies of dental development include several different methods, each useful for different
research questions. In order to describe the unique developmental patterns of primate
species, researchers have studied dental emergence patterns, rate of growth of the first
permanent molar, enamel secretion rates, and even the underlying dentinoenamel junction.
To focus specifically on modern humans, development of the teeth is one of the most accurate
ways to estimate age-at-death in subadults and dental wear is often useful in adult age
assessment.
Emergence Patterns
The study of dental emergence patterns is perhaps of most interest to those studying
primate and hominin dental evolution because the pattern differences between species indi-
cate different paces of life, or life histories. However, the pattern of emergence of the teeth is
also of use to those focused on modern human skeletal biology. It is useful to first point out
the difference between emergence and eruption. Emergence is a single moment in the move-
ment of the tooth when it breaks through either the gingiva or the alveolar bone. However,
eruption is the entire process of tooth movement as it grows and moves through the jaw and
soft tissues of the oral cavity.
The actual sequence of how teeth emerge into the oral cavity differs between species in
a way that reflects their overall life history. Species that develop quickly tend to exhibit rela-
tively early emergence of their permanent post-canine teeth while the emergence of the post-
canine dentition tends to occur later in the overall sequence for longer lived species (such as
humans) (
Box 10.1
). Because the order of emergence of the teeth is tied to both (1) ecological
independence (Can the juvenile successfully ingest the food it needs to once it is weaned?) and
(2) longevity (How long can these primary teeth hold up?) these sequences are under selec-
tion
3
for their ability to enable their carrier to process the food necessary to sustain life. Emer-
gence sequences are also heritable, which preserves a genetic component to their expression;
however, the selective effect mentioned above results in variation both within and between
species.
In modern humans, the general sequence of emergence of the permanent teeth is M1
I1
/
M3. This reflects later emergence of the permanent molars
due to an extended postnatal life. As a point of comparison, consider the relatively short-
lived Macaca nemestrina (pigtailed macaque) where the sequence is generally M1
I2
P3
C
P4
M2
/
/
/
/
/
/
I1
/
/
I2
M3. Due to the extreme sexual dimorphism in the canine
of the pigtailed macaque, there is a distinct difference in the emergence sequence between
males and females because of later canine placement in the sequence in males (
Smith, 1994
).
M2
P3
P4
C
/
/
/
/
/
3
See definition and explanation of natural selection in Cabana et al. (Chapter 16), this volume.
