age estimation from oral and dental structures 285
for when the tooth erupted).^128 Etiology of these annulations probably is due
to alternating cycles of mineralization of the cementum that is deposited as
dense bundles of collagen that are subsequently replaced (mineralized) by
hydroxyapatite crystals. Differences in the alternating light and dark bands
are due to their different crystal orientations.129,130
Counting cementum annulations is destructive, requiring histological
examination of thin sections through a root,131–133 and the method has some
limitations, among these are: different teeth from the same individual and
different sections from the same tooth yield different counts because cemen-
tum is not deposited uniformly; there may be some remodeling after deposi-
tion; some teeth exhibit thin or hard-to-read annulations; and annulations
may not necessarily be deposited annually.
Interestingly, the annuli show evidence of certain life history events that
negatively influence calcium deposition, such as pregnancies, and renal and
skeletal disease.^134 Such qualitative findings may be valuable in forensic iden-
tification cases.
Charles et al.^135 and Condon et al.^136 reported on a well-structured study
of teeth of known age. They found the correlation between true and pre-
dicted age was just 0.78, and there tended to be fewer lines than one per
year, but variably so. A few specimens exhibited doubling, where there were
about twice as many lines as anticipated from the person’s known age. These
authors made several observations: (1) archaeological specimens tend to have
fainter annulations (and should be decalcified more gently), (2) cementum
deposition may be affected by periodontal disease, (3) a few teeth possess
no cementum annulations, (4) accuracy of the method diminishes with the
person’s age, which is common to most aging techniques, and (5) population
differences need to be studied.^137 In spite of these several caveats, Condon
et al. noted that this method probably is at least as accurate as any other
skeleto dental technique.
Wittwer-Backofen et al. readdressed this issue of accuracy, providing
updated preparation methods and observational techniques (including scan-
ning electron microscopy).^138 They found that the error was just 2.5 years
or less (gauged from the 95% confidence limits), making the method more
accurate than many other approaches. This accuracy, however, was achieved
after about 16% of the sample was omitted where the cementum pattern was
irregular—“where the cementum band partly surrounds artifacts or overlays
itself in undulations”—or where image quality was poor after tissue process-
ing. These authors made the points that, in their hands, (1) males and females
could be aged with equal precision and (2) periodontal disease did not affect
accuracy.^134 They concluded, “This provides a strong argument for the appli-
cation of [this] method in archaeological skeletal samples in which most of
the individuals suffered from extreme dental disease.”^139