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ePaper created 2015-03-07, 18:13:20 | version 1.33.01
special _ forensic odontology I human DNA sequences are the same in every per- son, enough of the DNA is different to distinguish one individual from another, unless they are monozygotic twins. DNA profiling uses repetitive sequences that are highly variable, called variable numbertandemrepeats(VNTRs),particularlyshort tandem repeats. VNTR loci are very similar in closely related humans, but so variable that unre- latedindividualsareextremelyunlikelytohavethe same VNTRs. In situations in which a full nuclear DNA profile is not attainable, for example in an- cient or degraded remains, mitochondrial DNA analysis may be used, although with less certainty. Identification using DNA evidence relies on the comparison of an ante-mortem sample (reference sample) with a post-mortem sample, and may in- clude direct comparison of the decedent’s DNA (e.g. Guthrie cards or an ante-mortem blood sam- ple), or a comparison with relatives’ DNA (parents, children or siblings), to arrive at a conclusion. The conclusions of molecular biologists are expressed as a probability ratio and are thus scientifically quantifiable as to the strength of the match. With any DNA technique, the cautious juror should not convict on genetic fingerprint evidence alone if other factors raise doubt. Contamination with other evidence (secondary transfer) is a key source of incorrect DNA profiles, and raising doubts as to whether a sample has been adulterated is a favourite defence technique. Identification using fingerprints (friction ridges) relies on an examination of ante-mortem prints alreadyonfilewithauthorities(exemplars),ormore commonly comparison with latent prints retrieved from an object the subject of the examination was known to have touched. Fingerprint identification involves an expert, or an expert computer system operating under threshold scoring rules, determin- ingwhethertwofrictionridgeimpressionsarelikely to have originated from the same finger or palm (or toe or sole). The validity of forensic fingerprint evidence has been challenged by academics, judges and the media. While fingerprint identification was animprovementonearlieranthropometricsystems, the subjective nature of matching (especially when incompletelatentprintsareused),despiteaverylow error rate, has introduced an element of contro- versy. Medicalrecordcomparisoncanbeusedforiden- tification purposes when there is sufficient ante- mortemevidenceofuniquemedicalinterventionor disease. Examples include the discovery of medical prostheses,suchaspacemakersandprosthetichips, 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 areavailableforcomparisonwithpost-mortemexam- ination findings, positive identification is a relatively simple matter (Figs. 1a & b). For many cases, however, suchasimpleresolutionisnotsoeasilyachieved.Often ante-mortem dental records are incomplete or many yearsoldortherearenoradiographs.Couplethiswith incompleteremainsorremainsdamagedbyfireand/or trauma and the difficulties are magnified (Figs. 2a–c). Reproducing the exact angulation and aspect of an ante-mortem radiograph in a post-mortem radio- graph, 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 the tech- niquesavailable,butalsorequiresalevelofexperience and,intheearlyyears,adegreeofmentoring. Dental identification is not only achieved using comparison of restorations; other features of the teeth and maxillofacial skeleton may also be em- ployed. Root morphology, sinus configuration, un- usual crown shape, and pulp chamber morphology are all factors that can be considered in the absence ofrestorations,aslongastherearehigh-qualityante- mortem images with which to make a comparison. Study models, sport mouth guards, partial dentures, orthodontic appliances and photographs of the den- tition are all useful aids for a forensic odontologist and are employed with varying degrees of certainty, depending on the circumstances of the case. 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. I 35cone beam1_2015 Fig. 4