Forensic Dentistry, Second Edition

Forensic dental identification 173

Instead, he must make a quantitative and qualitative evaluation of the combi-
nation of features involved.”^11
Dr. Keiser-Nielsen’s interest was initiated by the acceptance of fingerprint
analysis in courts all over the world based on their accuracy and reliability.
Although standards varied in different jurisdictions at that time, in most,
when twelve concordant fingerprint characteristics could be demonstrated
in an antemortem and postmortem comparison, it was maintained that the
material must have originated from the same person. Keiser-Nielsen sought
to develop a parallel application for the field of forensic dental identification.
Specifically, he sought to quantify the probability that any two individuals
would have the same combination of teeth missing and present and teeth
restored and unrestored.
For the most fundamental problem, that of the presence or absence of teeth,

the mathematical expression is K

M

x

M

x

M

x

MX

MX, X

()

=

−−

→

−−

1

1

2

2

3

1

,

where M is the number of teeth considered, usually 32, and X is the number
of teeth missing. The same calculation could be done for other features, for
instance, the number of teeth with restorations.
Applied to the human dentition, Keiser-Nielsen proposed that even
greater discrimination could be established using combinations of features.
If only teeth missing/present and teeth restored/unrestored were considered
with no regard to which surfaces were restored, the formula involved cal-
culating the possible combinations for missing teeth, then multiplying that
number by the number determined by calculating the number of possible
combinations of restored teeth in the remaining teeth. Using Keiser-Nielsen’s
example of an individual missing four teeth and having four of the twenty-eight
remaining teeth restored, the formulae are:

For the four missing teeth, K 324

32 31 30 29

1234

, = 35 960,

×××

×××

= , representing

the number of different possible combinations for four missing teeth.

For the four restored teeth in the remaining twenty-eight, K28,4 =

28 27 26 25

1234

20 475

×××

×××

= , , representing the number of different com-

binations of four restored teeth among twenty-eight teeth.

Then by multiplying the two, 35 960 20 475,,×=736 281 000,,, Keiser-

Neilsen calculated that the number of possible combinations of a

person with four missing teeth and four restored teeth is 736,281,000.

In other words, the likelihood of any two people having the same four
teeth missing and the same four teeth filled (surfaces not considered) is 1 in
over 736 million, more than twice the number of people alive in the United
States (July 2008).