age estimation from oral and dental structures 291Because of overall inaccuracy, possible differences in interpretation
among evaluators, ethnic variation, and the fact that ethnicity is a com-
plex matter with poorly defined boundaries, several authors have cautioned
against relying too heavily on third molar formation alone for estimation
of age in late-adolescent/early-adult subjects as well as for determination of
attainment of adulthood.58,159 Various parameters of skeletal development
are also related to chronological age but, again, without sufficient accuracy to
ensure forensic certainty. Some studies indicate that using a combination of
dental and skeletal developmental findings results in increased accuracy of
age estimation. Schmeling et al., for example, recommend that age estimates
should be based on, in addition to dental radiological findings, general physi-
cal examination and radiological examination to determine stage of develop-
ment of the hand, wrist, and the clavicle.^159
Cameriere and coworkers^160 analyzed panoramic radiographs of Italian
subjects and found that the values resulting from the pulp-tooth area ratio of
the second molar and the stage of the development of the third molar com-
puted in combination resulted in better assessment of whether an individual
was eighteen or older than either method alone. Comparably, Chaillet and
Demirjian found that the addition of the third molar to Demirjian’s original
seven-tooth method increased accuracy of the estimate.^161
13.4.6 Aspartic Acid Racemization
Racemization of amino acids of certain proteins occurs in vivo.^162 This process,
the conversion of the L-isomer to the D-isomer toward equilibrium, proceeds
slowly throughout life, so it can be related to chronological age of the host and
therefore can be used forensically to determine age at death. Racemization
continues at a markedly reduced rate after death, so it is also useful for aging
archaeological samples.^163 It has been demonstrated in a variety of proteins
such as those in the eye lens,^163 brain, vertebral discs,^164 and dental tissues.^165
Many amino acids have been shown to racemize, and the process has been
described in all dental hard tissues.^162 Because of postmortem preservation,
a relatively high rate of racemization, and other technical factors, the com-
pound most often analyzed has been aspartic acid in dentine collagen.
Helfman and Bada first showed that age can be determined from the
enamel or dentin of a tooth by quantifying the relative amounts of the D- and
L-forms of aspartic acid.166,167 With time, the L-form undergoes racemization
to the D-form. Age estimation using racemization depends on the assump-
tions that (1) the aspartic acid has not been replaced by remodeling or by
diagenesis since the tooth was formed, and (2) the temperature has been con-
stant (as in the human mouth at 37°C). According to the claim put forth by
Helfman and Bada in their original publication^166 (p. 2893): “Under suitable
conditions, where there has been no racemization since death, i.e., relatively