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Challenging assumptions underlying bite mark comparison

Dr Pratik Tarvadi, Dr Richard Bassed, bitemarks, dentition, unique, skin as a registration medium, anatomical position, elasticity.
This slide articulates the two assumptions that underlie all of bite mark analytical theory. One, all teeth are unique, and two, that this uniqueness is accurately transferred into skin. Furthermore, there is the overarching assumption that the injury in the skin can be accurately recorded and reproduced with sufficient precision, such that it may be matched to a specific dentition to the exclusion of all others. These assumptions are demonstrably questionable, as we will see. The first assumption concerns the concept of dental uniqueness. In actual fact, this is completely irrelevant. Bite marks are delivered by a three dimensional set of teeth into a deformable and variable three dimensional curved substrate-skin.
And so, small areas of difference in dentition between individuals is never transferred into the injury. In essence, the injury is an imprecise and deformed representation of the teeth that made it. As we can see here, many dentitions are so similar in shape and arrangement that it is impossible to separate them without millimetric measurements and certainly not at all possible to discriminate between them based on an impression in skin.
This is the bite marks at different locations of the body. We can see that the forearm, we can see on the hand. We are being able to see it on the face, shoulder, different places, the bite marks are seen. And these bite marks vary with different severities. Severities can be also because of one major factor, that is the skin, which is a poor registration material. I have mentioned here due to location elastic property, this registration material means when I leave a mark here, if I cause a bite mark, this by the time my session will get over, this will either fade away or there will be swelling formed. That is the reaction of the body to the bite mark.
If I’m the victim or the culprit and I’m biting on somebody, then I need all the doctors around here. All the police officials. That as soon I bite, he should immediately go and give it. There is a lag time, at least of ten-fifteen minutes that the victim runs to the hospital. By that time, the mark is gone or swelling has taken place. That is because the skin is a poor registration material. Because it is based on anatomical location. Biting here, there’s a bone. So the teeth will get hampered and there will be only lacerations. Biting here, it is muscle with a little of fat. So there will be good impression here. But swelling also will be more.
Biting on the abdomen where there is a lot of fat or thighs, lot of fat. So there will be swelling more. Again, skin plays role there because of the anatomical location. Then underlying, as I said, bone, muscle, fat . Next, curvature. Here the bone is firm. Abdomen, bone is there so skin is firm. Here, abdomen fat is there so skin is loose. That also plays a role. Next, the age dependent. In children, elasticity is very good. So as soon as I do this, the time this has taken to come down, in children, it’ll be much faster. In young generations, up to the age of twenty-twenty five to be much faster, thirty to fifty it’ll be a little less.
And as seniors, it’ll take lot of time to relax. And when bite has occurred, there will be some stretching, elasticity. All that plays a role in the dynamics of biting, which also affects. Then comes whether it was ante-mortem, peri-mortem or post-mortem. Ante-mortem means before death. Peri-mortem is during the interface when there was a fight going on and the person died and post-mortem is after death. Many of the accused who first kill the victim and then sexually assault. So they cause the bite mark in post-mortem. So all these three also play a role in the skin. Then coming to the medical status of the individual.
If he’s suffering from bleeding disorder, then again, there is a different way the bite mark will appear. So all that combined makes skin a poor registration material because so many factors are responsible for the bite mark on the skin.

Does the discipline of bite mark comparison have a valid scientific foundation? Dr Bassed and Dr Tarvadi examine this question by challenging the assumptions on which bite mark comparison is based.

*References for images

Certain images in the video are sourced from ‘Jain N, Textbook of Forensic Odontology (2013)’.

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Decoding Forensics for Legal Professionals

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