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New study confirms that bitemarks on skin are highly distorted

There has been concern for sometime over the degree of distortion seen in human bitemarks on skin.  There is no doubt that it occurs and the first paper to really examine this was DeVore D.T., in his paper entitled “Bite Marks for Identification?”.  In this paper he used inked stamps (like a shooting target) and then measured them when living volunteers moved and flexed.  The results were conclusive – there is distortion and there is a lot of it.

Screen Shot 2015-10-10 at 13.29.26
Ink stamp used in the study – (C) Elsevier 2015

This latest paper – uses a similar technique but deploys a stamp made of denture teeth – to replicate more closely the appearance of a bitemark.  As with all research – there are limitations – there is no underlying injury here – however, the presence of diffuse bruising is unlikely to be very different – its a superficial phenomenon.

The research is presented in the Journal – Forensic Science International and written by Cheri Lewis and Leonar Marroquin from California State University. You can see the full citation of the work here.

What did they do?

The authors placed the inked teeth on a total of 40 participants shoulders and then asked each of them to move their arm in four different directions.  These were then photographed with the ABFO scale.  The authors measured inter-canine distances and individual tooth widths.

What did they find?

Like other authors (DeVore, Sheasby, Bush etc) they found that there were high levels of distortion present – the maximum tooth width distortion was 53.8%, and the maximum intercanine distance distortion was 41.9%.  Interestingly they found that older skin, and that with more sub cutaneous fat was more likely to distort than younger skin on thinner individuals

What does this mean?

Figure 2 from the work by Lewis & Marroquin (C) 2015 Elsevier
Figure 2 from the work by Lewis & Marroquin (C) 2015 Elsevier demonstrating the degree of distortion seen on the same anatomical location with four different positions of the arm.

This is very much a confirmatory study and many authors have reported similar findings – some using the same model (inked skin) and others using cadavers (Bush et al) or porcine skin (Dorion, Avon et al).  All, to one degree or another, report the same thing – that there is significant postural distortion present when recovering bitemarks from skin.

On living individuals one could argue that they may be able to recall the position they were in when bitter – but certainly this is not the case for deceased victims of biting.

The degree of distortion is huge – and in many ways these findings undermine the whole concept of individuality in the human dentition.  Previous studies have measured to fractions of a mm in their efforts to prove or disprove uniqueness – these data, and those from other studies, demonstrate that it just doesn’t matter – the distortion is too great for these measurements to be meaningful.

This paper – with its accepted methodological weaknesses – a single anatomical location, small (n=40) sample size and inked bites – adds further weight of evidence to those who would call for high levels of caution to be applied to bitemark evidence and that its use to include suspects should never be supported.

Scientific Abstract

Effects of Skin Elasticity on Bite Mark Distortion

Cheri Lewis, , Leonor A. Marroquin,
a 8500 Wilshire Blvd Beverly Hills, CA
b California State University, Los Angeles School of Criminal Justice and Criminalistics 1800 Paseo Rancho Castilla Los Angeles, CA 90032
Bite marks have been reported to have an evidentiary value similar to fingerprints. We believed bite mark distortion would impact the accuracy and reliability of bite mark interpretation. Inked denture-stamps were substituted for actual bite marks and were placed onto 40 participating volunteers’ shoulders. Four changes in arm position were photographed using an ABFO #2 reference scale. The measurements of individual tooth widths and intercanine distances in each position were compared. The maximum tooth width distortion observed was 53.8%, whereas the maximum intercanine distance distortion was 41.9%. Distortion was found to increase with age and weight and was non-uniform across a dental arch.

Originally sourced from: http://www.ncbi.nlm.nih.gov/pubmed/26451773?dopt=Abstract

About Odont1

Odont1 is a seasoned forensic dentist, researcher and educator with an interest in progressing the science of the discipline while retaining those elements that are evidence based and useful to the judicial system at any level.

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