354 Forensic dentistryuniqueness of the human dentition is not the important question, rather
“it is the rendition of these asserted unique features on human skin that is the
unknown quantity.”^61 Dentists understand the need for accurately depict-
ing complex features and routinely work with impression materials that
are capable of very accurately recording the features of the biting surfaces
of teeth. There is almost universal agreement among forensic dentists that
human skin is a very poor material for faithfully and accurately recording
those features. Most early bitemark-related papers that discuss skin con-
centrate on the distribution of bitemarks, the classification of bitemarks,
and the analysis of distortion in bitemarks or in preserved skin with bite-
marks.5,37–39,62–65 Although the earlier papers contained useful information,
until recently there has been a paucity of research by forensic odontologists
on the properties and behavior of human skin when bitten.66,67 In 2008 at
the AAFS meeting, a team of researchers from the State University of New
York, Buffalo (SUNY-Buffalo) presented four papers examining biomechani-
cal, macroscopic, and microscopic features of human skin and the features
seen in skin when the bitemarks are made through clothing. These studies
are a significant step toward a better understanding of bitten skin.68–71
Finding answers to questions regarding the features and behavior of skin
when bitten is crucial to establishing a scientific basis for bitemark analysis.
The SUNY-Buffalo team has since published the first article concerning the
biomechanical factors.^72 It must be demonstrated that teeth can or cannot
dependably transfer discernable features to skin during biting, and that those
features can be successfully imaged or recorded. Those features must then
be scientifically analyzable, the distortion accounted for, and a statistical or
mathematical basis for comparisons established.
14.4.3 Statistical and Mathematical Analyses
Relating to Bitemarks
As discussed in the section on the uniqueness of the human dentition, the
validity of any statistical and mathematical analysis of bitemarks is suspect
until the uniqueness of the human dentition is confirmed. To date, only three
significant papers have discussed or attempted this task.5 3 – 5 5 In each of these
studies, the statistical analysis problems center around the use of the prod-
uct rule. Also known as Leibniz’s law and the probability rule for indepen-
dent variables, the rule is most commonly applied to problems in differential
calculus. For forensic research applications the following definition may be
most useful: “The probability rule for independent variables, or product rule,
states that the probability of the simultaneous occurrences of two indepen-
dent events equals the product of the probabilities of each event.”^73 For three
or more independent events the multiplication of probabilities continues by
multiplying the product of the first two by the probability of the third and