Guest writer: David Harris is a freelance science communicator based in Maryland, USA. After graduating from the Australian National University with a University Medal in Theoretical Physics, he completed a Graduate Diploma in Scientific Communication. He spent three years as a PhD student at UQ but then moved to full-time writing and journalism in an attempt to satisfy his unquenchable thirst for science. David presented a weekly science program for ABC Radio, has worked in science television production and writes for a variety of national and international newspapers, magazines and websites. He is currently Head of Media Relations for the American Physical Society. Research team: Dr Alexander Forrest (Lecturer in Oral Biology, School of Dentistry and Queensland State Forensic Dentist), Dr Ian Davies (Assistant Forensic Dentist), John Garner (Digital Imaging Expert) Funding: Queensland Health Forensic Scientific Services (State Forensic Dentist position) In-kind support from Apple Computer and 3M Dental Email/Web link: a.forrest@mailbox.uq.edu.au www.uq.edu.au/dentistry/ Faculty of Health Sciences

"Better check the dental records" used to be the catchcry of dramatised police officers investigating a murder case. However, forensic dentistry has come a long way since then with high technologies leading the way in forensic identification.

Leading Australian advances in forensic dentistry is Dr Alexander Forrest in the UQ School of Dentistry and his team John Garner and Dr Ian Davies. With a research program driven by the demands of actual investigative cases, Dr Forrest neatly balances the basic research and clinically applied aspects of forensic science. He regularly works with police services and lawyers to develop techniques that are not only scientifically accurate but also legally acceptable.

From analysis of bite marks to facial reconstruction, the combination of his team's new techniques and extensive experience have meant that legal teams calling on his expertise have rarely lost a case.

"One of the main aims of forensic dentistry is to identify a person based on the limited evidence of tooth and face remains or marks left by teeth," Dr Forrest said.

"However, forensic dentistry can no longer always rely on checking dental records. People are far more mobile than in the past and often don't have the same dentist for their entire lives. In many cases, dental records simply do not exist."

Establishing a conclusive dental match is not always possible. For any comparison, there are three possible outcomes. The first is that dental evidence can exclude a possibility. Some mismatch can indicate that two records are incompatible or contradictory.

Second, there may be insufficient evidence. This occurs when all the data available is compatible with no inconsistencies but there is not enough evidence to reduce the potential matches to one person.

Lastly, an incontrovertible match can be made. This might happen via perfect matches of x-rays through to a large number of concordant points in dental records. Whatever technique is used, Dr Forrest will only state that he has found a match after reducing the uncertainty in the comparison to significantly better than one in the population of the world.

"One of the most problematic areas in forensic dentistry is the analysis of bite marks," Dr Forrest said.

Making a conclusive match between marks or bruises left on a soft and pliable substance with a real set of teeth in a jaw is a tough request at the best of times. However, Dr Forrest's team has developed a variety of techniques that have been used in law courts to provide evidence about the origins of bites.

"One of the techniques we are using in a preliminary way but still developing is the investigation of tooling marks from dragging teeth. A bite is rarely a static occurrence with teething sinking straight down. There is often a tearing or dragging of teeth over a surface," he said.

The marks left by the dragging action are characteristic of a particular set of teeth, just like those made by worn tools with slight imperfections or the rifling marks left on a bullet from the shape of a gun barrel.

"The forensic evidence for bite marks is sometimes essentially a two-dimensional record. However, the matching of three-dimensional teeth to even those records can be achieved," he said.

Dr Forrest makes casts of teeth from the jaw being tested and dips the teeth in ink to various depths to obtain contours, angled immersion studies and other data about how the solid teeth leave an impression or bruise on a flat surface.

Even this matching is fraught with difficulty because bite marks are often left in rounded surfaces. Working with Dr Peter Adams from the University's School of Mathematical and Physical Sciences, his team has developed computer techniques that can virtually "unwrap" tooth marks for comparison. This provides a meaningful demonstration to a jury about the amount of distortion caused by the curvature.

One great advantage of using teeth for identification is that they remain the same after death. The technique of visual comparison allows positive identifications to be made when a recent photograph of the victim is available.

"Essentially, we compare photographs of the person and of the remains. The technique is quite easy to perform and is astonishingly convincing when there is a proper match," Dr Forrest said.

Comparison of remains with dental records is rather subjective because it attempts to match a visual record of the remains with a written record, which says that certain teeth had particular shapes, flaws or fillings and is necessarily incomplete.

"With visual techniques, we can move from opinion-based evidence supplied by expert witnesses to objective evidence that juries can clearly evaluate for themselves," he said.

In a typical case, Dr Forrest will obtain a photograph of the suspected victim and pose the dental remains in the same way. Then a photograph of the remains will be scanned and corrected for scaling problems. The two images can then be compared digitally directly before a court.

"Every little bump and imperfection can be seen to match perfectly when a correct identification has been made. The jury can make this observation themselves, which I think is a great step forward. It minimises the problems associated with the influence of the personality of the expert witness. The evidence speaks for itself," Dr Forrest said.

When digital techniques come into play, great care needs to be taken to ensure that nothing could have been corrupted or modified. To counter objections about digital evidence, Dr Forrest can perform the entire comparison in front of a jury.

Combined with police records of the history of the evidence up until it reaches the courtroom, the whole process is open and transparent to a jury, with no room for impropriety.

Dr Forrest's team has developed strict protocols for the use of digital forensic dental evidence and they will be published for wider implementation soon.

In the horrific cases of discovered remains, identification of the body can be extremely challenging. The teeth and skull are often some of the few parts of the body that come through the tragedy relatively unscathed.

When there are no dental records for comparison with those teeth, other techniques are required. One technique that is proving successful is that of facial reconstruction.

"Starting with a skull, we are able to reconstruct an image of the face in about 90 minutes," Dr Forrest said.

"The biggest challenge with this technique is not in creating the reconstruction but persuading people to use it. As it is a relatively new technique, many in the law enforcement business are sceptical of its usefulness."

Of the dozen instances this technique has been used, nine have either generated a lead to solve the case or have proven a close match after the case was solved. The remaining three cases are still open but the reconstructions may also prove accurate. These results would indicate that the technique has greater applicability in crime investigation.

"First we determine the age, race and gender of the victim from the skull using well-established techniques. We then use a set of tissue-depth tables to determine what thickness of tissue should be on each part of the face," he said.

"Tissue-depth tables have been compiled over many years to give the average thicknesses of tissue at each point on the face for people of different ages, races and genders.

"We model these thicknesses by cutting pieces of rubber to the appropriate thickness for many points on the skull. Next we stick the rubber on the skull and photograph it.

"Finally, we digitally construct a face to fit the contours indicated by the rubber pieces, using standard anthropological guidelines. This image can give a very good representation of facial shape and form that doesn't need an expert to interpret or compare with a real person."

The theme behind all of the team's techniques is removing the human uncertainties inherent in analysis and current expert witness settings.

"My mission is the objectification of evidence," Dr Forrest said.

With his ongoing advances and development, Dr Forrest has given the once imprecise field of forensic dentistry a solid scientific basis that he can really get his teeth into.

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