Arguments on the Individuality of Human Teeth

 Back to Homepage

C. Michael Bowers DDS, JD


Author's note: The portion of this material that deals with the dental use of probability theory and the review of bite mark literature was presented by me at the 2000 American Academy of Forensic Sciences meeting in Reno, NV. The  authors of that paper were myself and Iain Pretty, B.D.S., M.Sc.


     The foundation of dental identification and bite mark analysis is that the total arrangement of a person's dentition creates a dental "profile" of sorts. An attempt to prove this was in 1982 when a small study of five identical twins was done at UCLA [i]. This investigation had nothing to do with dental restoration shape and position that are commonly used in identification of missing and unknown individuals. It was an attempt to test the differentiation of tooth shape and position within this small sample. The test involved pressing dental stone tooth models into a plaster of Paris substrate. There are experimental problems in this study involving the degree of depth necessary in a test bite mark to separate one twin from another twin. In bite mark cases having only two-dimensional discoloration (i.e bruising), the conclusion of this 1982 study is irrelevant. In addition, the authors published an opinion that conclusively establishes the uniqueness of the human dentition in their final statement, “(it is) clear that in terms of occlusal arch form and individual tooth positions, even so-called identical twins are in fact not dentally identical.” This is a seriously over-stated conclusion that has been perpetuated in the odontology literature.






  Figure One   Outlines of the same set of teeth. The different perimeter shapes depend on how far the teeth are pressed into the test substrate. (Thanks to Iain Pretty B.D.S., M.Sc.)

     The determination of uniqueness of the human dentition has a history in bite mark analysis that covers over four decades. The demonstration of uniqueness is a blend of art and opinion. The probability of more than just one person producing a similar or identical bite mark in a specific case is the challenge in every bite mark case and some identification cases.  The common leap of dental examiners, based on their “knowledge, experience, and training,” in testifying the low or insignificant probability of a false positive identification ignores common sense. Uniqueness will never be proven through statistics or studies like the one described above. Rather, the incidence of “false positives” or the “likelihood of a another set of matching teeth” is the direction to take. The forensic DNA community NEVER uses the word “unique” in describing the genetic profiles generated from both a suspect and crime scene evidence. They do state the chance of another’s profile being the same in statistical terms based on serious, prolonged and multi-reviewed studies.

     Legal commentaries from the 70's and 80's attacked bite mark analysis as a "new and unfounded science of identification" and that the "uniqueness of the human dentition hasn't been established."    The odontology response then and now is to hang its hat on a minima of journal articles, which wobble in their attempts to prove the assumption without much scientific rigor.

     A frequently used statement from experienced bite mark experts is "the controversy seems to hinge on how closely we look at the teeth and teeth marks."    This describes the odontologist's rule of thumb protection against false positive bite mark identifications. The weight given to a conclusion is based on the number of characteristics seen in the injury.  Probability of a positive match is often the result of how many tooth marks are seen in the injury, not in the uniqueness value (indeterminable, see supra) of each individual characteristic of either the defendant or the bite mark injury. Proof of uniqueness of specific dental characteristics, however, is unavailable in the scientific literature.

     The heavy use of probability theory is seen in the seminal bite mark articles of the last four decades. Their implication is that so many "points" of similarity or concordance between the bite mark(s) and a suspect's teeth assumes the fact that the dental features seen in the bite mark are unique to one person. .

     There is vague reference to the literature regarding what number of points of concurrence satisfies scientific standards for a bite mark identification. Keiser-Neilsen was never talking about bite marks when he introduced the use of the "product-rule " in 1960 [ii]. It was purely a theoretical use of simple probability theory assuming that each dental feature was independent of the next and the sum frequency of occurrence for a  "profile" could be used to establish the frequency of all the features occurring at once. He was actually talking about missing and filled teeth, not bite marks.  Rawson et al's 1984 paper on the "Statistical Evidence for the  Individuality of the Human Dentition" was a study utilizing teeth impressions in wax, which were then hand, traced and computer analyzed [iii]. Bite marks in skin were not the target of the 397 sets of wax teeth marks he choose to investigate out of a larger cohort of over 1200. This study is irrelevant regarding bite marks, a fact he alludes to within the body of the paper. The common use of this paper is to justify dental examiners’ positive identification statements regarding one person (the defendant) and a bite mark in skin.

     In order to achieve an accurate estimate of the frequency of the occurrence for a complex event, each feature (in this case the shape and position of teeth) has to be independent of each other. This is the basis for DNA population studies regarding genomic frequencies of various polymorphic loci. Each allele present at these loci (or tooth in this case) has to be proven to occur independently before being included in the calculations of the "product rule." Suffice it to say that Rawson et al. study did not achieve or even attempt to prove this. The scatter data available in his paper shows that the distribution of tooth positions was not proportional. Certain anterior teeth positions occurred less than others. The argument regarding the lack of independence of dental values (shape and position) was reported as a finding in a much earlier British paper that has been totally ignored since it was written [iv]. In essence, the use of uniqueness of the human dentition and probability theory regarding bite mark analysis is flawed.

Tooth Number







Position data







Tooth Number







Position data










Figure Two

Data showing “possible positions” for the six upper and lower teeth as seen in the "Statistical Evidence for the Individuality of the Human Dentition." The frequency of occurrence varies within each upper and lower sample. If each tooth were independently occurring, the numbers would be similar for contra lateral teeth. For instance, the lower set values of 116.0 and 153.5  are for the two lower front teeth. This is a variance of occurrence of nearly 50%.


     Not all bite marks have the level of forensic value necessary to identify just one individual. Toolmark terminology was adopted early on by odontologists regarding the types of dental features seen in bite marks and the human dentition. A characteristic within a bite mark or in a person's dentition is a distinguishing feature, trait, or pattern. A class characteristic reflects a feature of generic value to a large population. Each human tooth has shape and position features common to the human species. The diagnosis of a human bite mark is dependent on the presence of these class characteristics being present in the injury.

     Individual dental characteristics are reported to be features that are unique to an individual variation within a defined group. The presence of worn, fractured or restored teeth is valued as unique features. If a bite mark possesses the reflection of such a feature(s), the degree of confidence in a match increases.   The odontological literature is silent regarding the frequency of these traits. It is actually counter-intuitive to assume enamel chips, fractures, and dental restorations are ALWAYS inherently unique. The shape of human teeth is quite constant in nature and their changes over time are based on common events. The chance occurrence of more than one person having a crooked front tooth is quite large. That is why orthodontists have such large practices.

In a law text published in 1997, Rawson [v] stated that a concordance between the biter and the injury is assured by the presence of the following:


" Missing teeth, pattern of rotation, angulation or position of each tooth…

 if the frequency of certain positions is known for the general population ."


This has not been accomplished by the forensic literature.

     Rawson continues in this vein by adding up the hypothetical frequencies of occurrence of more rare or in his terms "uncharacteristic features." He then arrives at the use of "product rule" probability per Keiser-Neilsen, based on the assumption that these features of higher forensic value are independent of one another.  This is conceptually flawed and points to the leap of logic that is a foundation of bite mark analysis.

     Incumbent to this process is the total assumption that human uniqueness determination of dental characteristics is possible. As stated supra, this author is of the mind that the real test is how often someone else's teeth could match the pattern seen in a bite mark.


[i] Reidar Sognnaes et al, Computer comparison of radiographic bitemark patterns in identical twins, 105 J. Am. Dental Ass’n 449 (1982).

[ii] S. Keiser-Nielsen, Person identification by means of the teeth (1980).

[iii] 29 Journal of Forensic Sciences 245 (1984).

[iv] TW MacFarlane et al, Statistical problems in dental identification, J Forensic Sci Soc;14(3): 247-52 (1974).

[v] Faigman, Kaye, Saks, Sanders, Modern scientific evidence, Vol 2, West Publishing, (1997), 168.