Forensic Dentistry, Second Edition

age estimation from oral and dental structures 269

limited by small, varied sample sizes and weak study designs. The early work

by Fanning sheds some light here. She showed that the effect of extraction

depends on the eruption status of the successor, specifically, how developed

the root is and how much overlying bone there is. If extraction was done when

the successor was deep in its crypt with appreciable overlying bone and less

than about one-fourth of the root formed, emergence is delayed. Conversely,

if extraction was done when the successor was already close to the alveolar

crest and there is considerable root formation, emergence is accelerated.^41

13.2.1 Statistical Concerns

While tangential to this review, investigators and researchers need to be
aware of the diversity of statistical techniques used to calculate the “average”
age of a tooth’s emergence (and of other developmental events). One issue is
that the data can be derived from longitudinal or cross-sectional data. With
longitudinal data, how frequently were the exams made? The precision of
timing is one-half the examination interval, so broader-spaced examinations
reduce the precision of the estimate of when a tooth emerged. When a tooth
is unerupted at one exam but is erupted at the next, the convention is to
assume that the tooth actually erupted halfway between the two exams.^42
With cross-sectional data, where children of various chronological ages are
examined just once, various statistical methods have been applied to estimate
the average age, but these don’t all produce the same results because they are
based on different assumptions. Methods range from calculating the arith-
metic mean of the chronological ages of children exhibiting the tooth43,44 to
calculating probits or logits.^45 Analysts have applied other methods that are
purported to better fit the nature of the data.46,47
Shortcomings of using tooth emergence to gauge a person’s age are
(1) tooth emergence is a fleeting event that occurs at an instant in time—a
tooth can only be unemerged or emerged—and (2) permanent tooth erup-
tion occurs within a span of only about 6 years (ignoring the highly variable
M3), so the method is of no use outside the range of about six to twelve years
of age.

13.3 Tooth Mineralization

Tooth mineralization—the development of a tooth’s hard tissues—spans a

much longer age range, making it more broadly applicable than emergence.

S o to o, t he e x t ent of m i ne r a l i z at ion c a n b e gau ge d r a d iog r aph ic a l ly s o it i s non-

invasive. (We prefer tooth mineralization to the older term tooth calcification

because little of a tooth’s substance is calcium per se.)