Biology Reference
In-Depth Information
M1 and I1 emerge in a very short time frame, while in the apes and australopithecines I1
emerges roughly 2
e
2.5 years after M1 (
Dean and Wood, 1981
). The increased clarity of the
CT images obtained in Conroy's study made it possible to confirm that in this specimen,
the permanent central incisors were still developing and had just begun root growth, which
is a lesser stage of development than would be expected if the specimen in question was on
a modern human developmental trajectory.
It has been demonstrated that scoring standards developed for scoring traditional X-rays
can be adapted for use with CT images of the developing dentition (
Coquerelle et al., 2010
).
However, CT scanning remains a costly method that is often used for analysis of single spec-
imens rather than the creation of population standards. For example, CT has been used to
study dental wear and pathology in mummies (
Melcher et al., 1997; Cesarani et al., 2003
)
although standardization of interpretive methods is yet to be done (
Chhem, 2006
). Still,
others working with mummies have continued to use traditional dental or cephalometric
X-ray imaging for the interpretation of dental growth and wear even when using CT to study
the rest of the body (
Previgliano et al., 2003; Kieser et al., 2004
). In a forensic context, CT has
been shown to be useful in aging fetuses and neonates by both dental and skeletal develop-
ment (
Sakurai et al., 2012
).
In addition to the benefit of being able to distinguish between different materials that may
be lodged in the dental and facial area, the smaller pixels of three-dimensional (3-D)
microtomographic scans are able to distinguish between different portions of the tooth
(enamel, dentin, pulp chamber) and to present, store, and analyze images in three dimen-
sions. In this manner, the study of the topography of crown and root morphology and the
enamel
e
dentin junction can progress beyond two-dimensional analyses at different sections
along the tooth crown. Discrete metric analysis is also aided by the digital environment in
which modern CT images are processed and viewed with the availability of 3-D landmark
and volume analysis (
Olejniczak et al., 2007
). For more information on the applications of
CT imaging, see Moore (Chapter 14), this volume.
Micro-CT
More recently, a special type of microtomography called phase-contrast X-ray synchrotron has
been employed by dental anthropologists. This method is unique in that it allows the study of
incremental tooth growth with exceptional clarity, enabling researchers to view and analyze
tooth microstructure. Previously, determining such important developmental markers such
as Retzius line periodicity would have required traditional, destructive histological tech-
niques, as discussed earlier. Recent developments and research at the European Synchrotron
Radiation Facility in Grenoble, France have provided researchers with a new way to assess
such structures in precious fossil material without the need for sectioning. See
Tafforeau
and Smith (2008)
for a thorough summary of the recent developments in this area.
Imaging Methods as Research Tools
In terms of studying dental development and teeth in general, consider the differences
between traditional dental X-ray, dental histology, and CT. Understanding the benefits and
limitations of different methods of analysis such as this is important when designing a study,
particularly when it involves large numbers of specimens (
Table 10.2
).
