age estimation from oral and dental structures 275were derived from the cross-sectional study of children attending a dental
school in Tennessee for routine dental care (Tables 13.8 and 13.9).13.3.3 Dental Age
Investigators should score all formative teeth in order to maximize the
information about a case. An exception would seem to be dysmorphic teeth,
including microform and pegged teeth, where the formative status is ques-
tionable. In Westernized settings, where the subject may have been exposed
to chemotherapy or irradiation during growth, one needs to be alert to abnor-
mal crown-root forms.77–79 Alternatively, no one has found any consistent
left-right asymmetry in tooth formation,^20 though mandibular teeth tend to
form and erupt slightly ahead of their maxillary counterparts.80–82
In concept, the formative status of up to thirty-two permanent teeth could
be scored for a given individual, though the incisors may have completed root
apexification before M3 mineralization begins.^15 The question is how best to
synthesize the age estimate. It is unlikely that multiple teeth will yield the same
age estimate. The simplest suggestion for combining the individual tooth age
estimates is to average across all scorable teeth.61,83 The shortcomings are that
(1) much of the data are redundant (such as estimates from homologous teeth
on the two sides of the arcade), and (2) some teeth are more precise and reliable
estimates than others (though this is a complex mix of tooth type and stage of
formation). The third molar is notorious in this regard, with unusually high
variability, and it is omitted from some scoring systems.
Demirjian et al.^62 developed a weighting scheme to overcome these issues.
With his system, the mandibular seven tooth types are scored (omitting M3).
Just the mandibular teeth are used because of their greater clarity on radio-
graphs (whereas several maxillary teeth are obscured by the complex bony
architecture), and because there is considerable statistical redundancy among
the teeth in the two arches. Likewise, teeth from just the left (or from the
clearer, better preserved) side are used because of the duplication of informa-
tion between sides. There are four steps in the Demirjian system: (1) the extent
of crown-root development of the seven teeth is scored (Figure 13.4), (2) a table
of values is used to weight each tooth’s score, (3) these weights are summed,
and (4) the sum is checked against another table that provides the person’s
dental age. Several researchers have computerized this sequence of events to
minimize the arithmetic.^62 Demirjian’s system has been applied to a variety of
ethnic samples.57, 8 4 Results have been varied, and those where dental age pre-
diction has been poor occur because the target sample has a different tempo of
growth during childhood or adolescence than the French Canadians used to
develop the pattern.18,85–87 That is, the dental age curve developed mathemati-
cally from Demirjian’s French Canadian children is not uniformly applicable
to other human groups. Deviations commonly are greatest in adolescence,