Biology Reference
In-Depth Information
course of development. This has important implications for both paleoanthropology and
forensic applications ( Dean et al., 1993 ). See Trammell and Kroman (Chapter 13), this volume,
for more information about dental and bone histology.
Cementum Annulation
Dental cementum is a living tissue that continues to grow throughout life. It is the calcified
material that covers the outside of the tooth root, and provides the attachment site for the
periodontal ligaments which hold the tooth to the alveolar bone within the socket. When
looking at a horizontal slice through a tooth root, one can observe the layer of cementum
covering the root. Under a microscope, alternating light and dark bands are visible. Because
of the assumed annual periodicity of cementum annulations, counts of the naturally alter-
nating light and dark bands that are characteristic of dental cementum formation have
been used for estimating age-at-death in various animals, though the etiology is unclear
( Charles et al., 1986 ; Hillson, 1996 ).
As discussed previously in this chapter and elsewhere in this volume, available skeletal
and dental aging techniques are much more accurate on subadults as the processes that
govern development are under rather strict genetic control (more so for teeth than the skel-
eton). The degenerative changes that are used to estimate age in adult skeletal and dental
remains are inherently more variable due to environmental, individual lifestyle, and genetic
differences that affect the various degenerative processes. Once tooth growth is completed,
age estimations using the teeth must be based on dental wear. However, cementum annula-
tion is a process that continues throughout life and thus holds great promise as a way to
obtain age-at-death estimates in adults.
Age estimates using cementum annulation are made by adding the average age of emer-
gence of the tooth to the number of dark and light line pairs counted because (1) cementum
growth begins once the tooth is nearing functional occlusion and (2) it is assumed that each
count of a light and dark band roughly equals one year of growth. Although the exact mech-
anism for formation of cementum annulations is still unclear, it appears that seasonal varia-
tion plays a large part in the degree of expression ( Charles et al., 1986 ).
A primary challenge in the use of cementum annulations is the replicability of line counts,
i.e., intraobserver and interobserver error. Part of the methodological complexity is in the
difficulty inherent in reliably obtaining quality, readable slices for analysis in addition to
the added step of having to slice the tooth (and thus damage it). Some authors report consid-
erable difficulty in obtaining readable slices ( Jankauskas et al., 2001; Renz and Radlanski,
2006 ). Furthermore, sections taken from different areas of a single tooth and sections taken
from different teeth within the same individual can produce different counts. There is also
no clear consensus on which tooth or portion of the root should be used to obtain the
most accurate count ( Renz and Radlanski, 2006 ). As pointed out by Renz and Radlanski
(2006) , if different teeth or even different portions of teeth display incongruous counts
then the method would be less than desirable as a reliable indicator of age.
Once a readable slice is obtained, the thickness of a slice can also impede the ability of
researchers to take reliable counts due to the superimposition of lower layers. Both Charles
and colleagues (1986) and Condon and colleagues (1986) suggest demineralization of the
tooth in order to obtain thinner slices to avoid this issue. They report obtaining significantly
Search WWH ::




Custom Search