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Trends & Applications DENTALTRIBUNE Asia Pacific Edition No. 1+2/201522 been devised and so a degree of expert subjectivity is still required. Prior to the availability of sci- entificmethodsapplicabletothe issue of positive human identifi- cation, the only real option for relatives and friends to recover themortalremainsoftheirloved ones was to visually examine them, and make a decision re- garding whether the person be- fore them was indeed who they believed him or her to be. On the face of it, positive human iden- tification by visual recognition would seem to be a fairly simple matter, as long as the deceased has undamaged facial features. Wecan allrecognise people who are well known to us by their facial features and mannerisms, even in poor light and at odd angulations. This has been shown to be true in many studies concerning the recognition of living people via CCTV security footage. Why then are there doc- umented cases of misidentifica- tion through visual recognition of the deceased, even of intact and undamaged faces? Theprocessofvisualrecogni- tion is complex and until quite recently not well understood. Clues as to the identity of an indi- vidual, either living or deceased, rest not only with the physical structureoftheface,butalsowith the variety of facial expressions, the display of various manner- isms, and the context in which the individual is seen. A deceased person has lost all facial expression, animation, and context and simply looks different from when he or she was alive. Incipient decompo- sition changes may also be present and go unrecognised. Couple this with the stress and trauma being experienced by the identifier, who may well have never seen a dead body before, and it is easy to see how someone may make a mistake. This is compounded by the way visual identifications are often performed, in that the deceased is presented to the identifier to confirm what the authorities already believe they know. Identification methods Visual recognition, despite the lack of scientific validity and the propensity for error, will for all practical purposes remain as a major method for positive human identification. When it is determined that vi- sual recognition is not an op- tion, usually because of trauma, incineration, decomposition, or multiple deaths resulting from a single incident, then forensic practitioners are able to rely on more scientific means to determine identity. The common methods employed include molecular biology, medical record comparison, fingerprints, and dental record comparison. DNA profiles are encrypted sets of numbers that reflect a person’s DNA make-up, which can also be used as the person’s identifier.Although99.9percent of human DNA sequences are the same in every person, enough of the DNA is different to distinguish one individual from another, unless they are monozygotic twins. DNA profil- ing uses repetitive sequences that are highly variable, called variable number tandem repeats (VNTRs), particularly short tan- dem repeats. VNTR loci are very similar in closely related hu- mans, but so variable that unre- lated individuals are extremely unlikely to have the same VNTRs. In situations in which a full nuclear DNA profile is not at- tainable, for example in ancient or degraded remains, mitochon- drial DNA analysis may be used, although with less certainty. IdentificationusingDNAevidence relies on the comparison of an ante-mortem sample (reference sample) with a post-mortem sample, and may include direct comparison of the decedent’s DNA (e.g. Guthrie cards or an ante-mortembloodsample),ora comparison with relatives’ DNA (parents,childrenorsiblings),to arrive at a conclusion. The con- clusions of molecular biologists areexpressedasaprobabilityra- tio and are thus scientifically quantifiable as to the strength of the match. With any DNA tech- nique, the cautious juror should not convict on genetic finger- print evidence alone if other fac- tors raise doubt. Contamination with other evidence (secondary transfer) is a key source of incor- rect DNA profiles, and raising doubts as to whether a sample has been adulterated is a favourite defence technique. Identification using finger- prints (friction ridges) relies on an examination of ante-mortem printsalreadyonfilewithauthor- ities (exemplars), or more com- monly comparison with latent prints retrieved from an object the subject of the examination was known to have touched. Fin- gerprint identification involves an expert, or an expert computer system operating under thresh- old scoring rules, determining whether two friction ridge im- pressions are likely to have orig- inated from the same finger or palm (or toe or sole). The validity of forensic fingerprint evidence has been challenged by academ- ics, judges and the media. While fingerprint identification was an improvement on earlier anthro- pometric systems, the subjective nature of matching (especially when incomplete latent prints are used), despite a very low er- ror rate, has introduced an ele- ment of controversy. Medical record comparison can be used for identification purposeswhenthereissufficient ante-mortem evidence of unique medical intervention or disease. Examples include the discovery of medical prostheses, such as pacemakers and prosthetic hips, which will have engraved on them serial numbers, which can then be reconciled with ante- mortem surgical notes. Dental identification When good quality ante- mortem dental records are avail- able for comparison with post- mortem examination findings, positive identification is a rela- tivelysimplematter(Figs.1).For many cases, however, such a simple resolution is not so easily achieved. Often ante-mortem dental records are incomplete or many years old or there are no radiographs. Couple this with incomplete remains or remains damaged by fire and/or trauma andthedifficultiesaremagnified (Figs. 2a–c). Reproducing the exact angulation and aspect of an ante-mortem radiograph in a post-mortem radiograph, taken in less than ideal circumstances, can also be challenging. In order to reach conclusions to these difficult identification puzzles, the forensic dentist not only needs a solid grounding in all of thetechniquesavailable,butalso requires a level of experience and,intheearlyyears,adegreeof mentoring. Dental identification is not only achieved using comparison of restorations; other features of the teeth and maxillofacial ske - letonmayalsobeemployed.Root morphology, sinus configura- tion, unusual crown shape, and pulp chamber morphology are all factors that can be considered in the absence of restorations, as long as there are high-quality ante-mortem images with which to make a comparison. Study models,sportmouthguards,par- tial dentures, orthodontic appli- ances and photographs of the dentition are all useful aids for a forensic odontologist and are employed with varying degrees of certainty, depending on the circumstances of the case. Personal identification via dental record comparison is similar to fingerprint analysis in that there is, as discussed above, an element of subjectivity in- volved in the matching process. Where dental identification dif- fers, and is perhaps easier to comprehend for lay people, is in the nature of the evidence being compared.Withdentalevidence, matches are commonly assessed by comparing both ante-mortem and post-mortem radiographs of easily identifiable man-made (and most often handmade) restorations. Unlike the minute nature of the whorls and swirls of fingerprint evidence, dental radiograph comparisons are of- ten so obviously similar that any reasonable person is able to say that the images belong to the same person. Other aspects Asidefromidentificationcase work, odontologists are asked toprovidemedico-legalopinions on a variety of topics as outlined in the introduction. Bite mark interpretation is probably the most recognisable of these to the lay audience and involves the assessment of injuries to the skin that are suspected of being caused by human teeth. This area of forensic practice is fraught with difficulty, as the highly subjective nature of the conclusions reached is almost completely based upon opinion rather than scientific research. There are so many problems as- sociated with the interpretation of bite marks that to describe them all here is beyond the scope of this introductory article. Cranio-facial trauma analy- sis is a growing area of forensic odontology practice, and in- volvesexaminationofbothliving anddeceasedindividualsandthe provisionofopinionsconcerning accurate anatomical description of the injuries (Fig. 3), degree of force (mild, moderate severe), and direction of force applica- tion. Occasionally, opinions are also sought regarding the exact nature of the weapon used, al- though caution needs to be exer- cised in this regard, as unless the implement bears unique charac- teristics that are imparted to the body interpretation will be very difficult. This area of odontology practice predicates a thorough knowledge of cranio-facial ana- tomy, the biomechanics of bone, and the effect on anatomical structures of various degrees of force. Age estimation has always been a function of the forensic odontologist, and traditionally has been based upon interpreta- tion of dental development and comparison with published stan- dards for tooth development (Fig. 4). The majority of age esti- mation work has concentrated on the ageing of children up to 15 years. Beyond this age, dental development becomes relatively unreliable, as only the third mo- lar is available for assessment, and this tooth is notoriously vari- fl page 21DT Figs. 5a–c: Multiple development sites used for age estimation of late teenage individuals: in this case, the third molar, the medial clavicular epiphysis, and the spheno-occipital synchondrosis, all of which are useful age indicators in the late teenage years. Fig. 3: An example of cranio-facial trauma in a homicide case. Accurate injury description can be vital in these cases.— Fig. 4: Age estimation using a standard atlas of development results in an age range that can either lead to identification or help police in limiting their search criteria for a missing person in the case of discovered unknown remains. Fig. 3 Fig. 4 Fig. 5a Fig. 5b Fig. 5c DTAP0115_21-23_Bassed 09.02.15 11:01 Seite 2 DTAP0115_21-23_Bassed 09.02.1511:01 Seite 2