Reality bites--A ten-year retrospective analysis of bitemark casework in Australia

Criticism of forensic science, particularly that of bitemark analysis, has become increasingly common in the last decade. Much of the criticism directed at forensic odontology cites cases where miscarriages of justice have occurred when erroneous, over-confident or even false bitemark evidence has been tendered by odontologists. Despite Australia's own experience with such cases in the past, it is postulated that this does not represent the true nature of bitemark analysis as practiced by odontologists today-at least in this country. A review of 119 cases from the last 10 years confirms that 'identification' of a suspect is rarely, if ever, offered, and that conclusions reached by odontologists with respect to bitemark analysis are generally conservative. However, the results of this study also indicate that in a small but significant proportion of cases, there is still some tendency to reach conclusions that could be considered over-confident when considering the overall quality of the physical evidence offered. It is suggested that odontologists should avoid making conclusive remarks regarding the origin of the mark, or the identification of a perpetrator, when such comments are realistically precluded, given the low evidentiary value of the mark itself.     

Problem-based analysis of bitemark misidentifications: the role of DNA

The dental literature concerning bitemark methodology is surprisingly thin and sorely lacking in rigorous scientific testing. Contra to this fact, the bitemark legal caselaw is surprisingly strong and is used as a substitute for reliability testing of bite mark identification. In short, the Judiciary and the Prosecutors have loved forensic odontologists. This paper will focus on the author's participation as a Defense expert over the last seven years in over 50 bitemark prosecutions and judicial appeals. This sampling will act as an anecdotal survey of actual bitemark evidence. Certain trends regarding methods and reliability issues of odontologists will be discussed. Several of these cases have been later judicially overturned due to DNA analyses after the defendants were originally convicted. These diagnostic misadventures are being vocally discussed in the US media by news and legal investigators who are asking hard questions. The forensic dentistry community, however, is curiously silent. What actions are necessary by the profession to improve this assault on the 52-year tradition of bite mark identifications in the United States?     

Results of the 4th ABFO Bitemark Workshop--1999.

Thirty-two certified diplomates of the American Board of Forensic odontology (ABFO) participated in a study of the accuracy of bitemark analysis. Examiner experience as board-certified odontologists ranged from 2 to 22 years.Examiners were given sets of photographs (a cast in 1 case) of 4 bitemark cases and asked to report their certainty that each case was truly a bitemark and the apparent value of the case as forensic evidence. Participants also received 7 occluding sets of dental casts, 1 correct dentition for each case and three unrelated to any of the cases, and asked to rate how certain they were that each set of teeth had made each bitemark. Receiver operating characteristic (ROC) analysis resulted in an accuracy score of 0.86 (95% CI=0.82-0.91). Youden's index was used to determine a cutoff point for determining an accuracy score for each case. Accuracy scores were significantly correlated with bitemark certainty and forensic value (P<0.001 in both cases) but not with examiner experience (P=0.958). The use of individual ROC analysis with weighted Youden's index to calibrate individual accuracy was also demonstrated.     

Anatomical location of bitemarks and associated findings in 101 cases from the United States

The purpose of this paper is to update and confirm previous studies that examined the anatomical location of human bitemarks. This information is useful to forensic odontologists and pathologists, physicians, and coroners who must be familiar with the most likely locations of bitemarks. The data are also useful for those involved in bitemark research. Using the legal database "Lexis," 101 bitemark cases were identified from the United States Courts of Appeal. Cases were included in the study if they provided details concerning the bitemark, such as anatomical location, number of injuries, and information concerning the victim. Information on 148 bites was collated. These data are presented in tabular and graphical form to allow comparisons between males and females, victims and perpetrators, adults and children, and the crime types associated with human bites.     

Expert Disagreement in Bitemark Casework*

Abstract: Bitemark cases continue to raise controversy due to the degree of expert disagreement which is frequently seen. Using a case mix of 49 bitemark cases from 2000 to 2007 each injury was independently assessed for its forensic significance using a previously described bitemark severity scale. Following the assessment, the mean value for the bites was categorized according to the crime type, the degree of expert agreement, and the judicial outcome. Results suggest that bitemarks found in child abuse cases have statistically significantly lower forensic value than those in other crime types, that bites where there is mutual agreement between experts will have higher forensic value than those where there is disagreement at trial, and that cases in which DNA has provided an exoneration will demonstrate similar quality to those where a conviction was secured. Forensic odontologists should carefully assess bitemark evidence and ensure that it meets certain minimums in relation to the presence of class and unique features before undertaking an analysis.     

Expert Interpretation of Bitemark Injuries—A Contemporary Qualitative Study

This study attempts to characterize the nature of disagreement among odontologists in determining the fundamental properties of suspected bitemark injuries. Fifteen odontologists were asked to freely comment on six images of supposed bitemarks. Qualitative analysis using a grounded theory approach revealed that practitioner agreement was at best fair, with wide‐ranging opinions on the origin, circumstance, and characteristics of the wound given for all six images. More experienced practitioners (>10 years) tended to agree with each other less than those who had 10 years or less experience in forensic odontology. The differences in opinions can be at least partly accounted for by the inconsistent nature of approaches used by different practitioners in assessing bitemark evidence. The results of this study indicate that more definitive guidelines as to the assessment of bitemarks as patterned injuries should be developed to ensure the highest possible level of practitioner agreement.     

The barriers to achieving an evidence base for bitemark analysis

Forensic dentistry is the union of two scientific disciplines, both of which are undergoing a renewed scientific rigor. In forensic science the advent of the Daubert ruling has required that judges assess the forensic value of 'expert testimony' ensuring that techniques, methodologies and practices are not only commonly accepted (as was the previous hurdle during the Frye era) but that error rates, assessment of reliability and validation studies are published to support their use. This new degree of judicial scrutiny has been mirrored in the field of dentistry itself, where organisations search and summarise randomised controlled trials in order to recommend best practice and devise clinical care pathways that are firmly grounded in proven scientific research. Despite the obvious drive from both of these professions, forensic dentistry, and in particular the sub-discipline of bitemark analysis, has been remarkably slow to address the obvious deficiencies in the evidence base that underpins this element of forensic science. Reviews of the literature reveal that the vast majority of published works are case reports, and very little primary literature exists. This paper reviews those studies that have assessed aspects of bitemark analysis including the crucial issue of the uniqueness of the human dentition; the application of transparent overlays and the application of statistical probabilities in bitemark conclusions. There are numerous barriers to undertaking high quality research in the field of bitemark analysis, the most important of which is the use of a gold-standard that is acceptable both in terms of diagnostic research but is also forensically relevant. If bitemark analysis is to continue to play a role in the judicial process then there is an urgent need for high quality studies that meet the levels of forensic and scientific scrutiny applied to other disciplines within the criminal justice system. Studies are required to determine not that the human dentition is unique, but how this asserted uniqueness is represented on human skin and other substrates. The error rates associated with the analysis of bitemarks are required on a procedural level as well as an individual practitioner basis and scales and interpretative indices of bitemark severity and forensic significance should be validated and introduced into common use.     

Three‐Dimensional Comparative Analysis of Bitemarks*

Abstract: Historically, the inability to accurately represent bitemarks and other wound patterns has limited their evidentiary value. The development of the ABFO #2 scale by Krauss and Hyzer enabled forensic odontologists to correct for most photographic plane distortions. The technique presented here uses the ABFO #2 scale in conjunction with the evolving technologies of laser scanners and comparative software commonly used by the automobile industry for three‐dimensional (3D) analysis. The 3D software comparison was performed in which measurements were analyzed of the normal distance for each point on the teeth relative to the bitemarks. It created a color‐mapped display of the bitemark model, with the color indicating the deviation at each point. There was a correlation between the bitemark and the original teeth.     

The scientific basis for human bitemark analyses--a critical review.

This article presents a discussion of the scientific basis for human bitemark analyses. Using a review of the literature, the major areas of contention within the field are assessed: including the accuracy of bitemarks on skin, the uniqueness of the human dentition, and analytical techniques. The review revealed a lack of valid evidence to support many of the assumptions made by forensic dentists during bitemark comparisons. The new level of judicial scrutiny of such scientific evidence is likely to emphasise this lack of knowledge upon which bitemark analysis relies. The authors call for a more scientific and evidence-based approach to forensic dental research.     

Adherence of forensic odontologists to the ABFO guidelines for victim evidence collection

Certifying boards for different professions have the duty to help establish standards and guidelines for methodologies routinely performed within the discipline. For forensic dentists, this responsibility is placed upon the American Board of Forensic Odontology (ABFO). The purpose of this study was to examine whether board certified and noncertified forensic odontologists adhere to the ABFO Guidelines outlined in the collection of victim bitemark evidence. A questionnaire was developed to assess the compliance and attitudes towards the typical evidence collected, the photographic documentation, and the handling of the bite site injury. The results indicate the majority of the respondents in both representative groups routinely follow the guidelines set forth by the ABFO. The lack of personally photographing the bite injury on a consistent basis is an area of concern for all examiners. The photographic evidence is an instrumental part of the investigation and often cannot be utilized due to improper procedures being followed. The film type utilized, bite site impression techniques, and excision of any tissue samples remain an individual choice and vary significantly among each forensic odontologist.     

Context effects and observer bias--implications for forensic odontology

Psychologists have long recognized the effects of contextual and extraneous information on decision making. Such information renders the subject susceptible to both motivational and cognitive bias; yet, it is difficult to assess the extent to which these influence forensic odontologists opinions as there have been no studies to date on this subject. This article explores the various types of contextual effects and biasing influences that potentially impact on the analysis of bitemarks in forensic odontology. It appears that the current practice of bitemark analysis is rich in sources of potentially biasing influences. In addition to the fundamental recognition that some form of bias is likely to exist, ways in which these should be minimized include: separation of the collection and analysis phases; limiting the amount of contextual information available to the odontologist responsible for the analysis; and ensuring that evidence that is ambiguous or of poor quality is identified as such prior to analysis.     

Dentists' qualifications affect the accuracy of radiographic identification

This study assessed the effects of forensic odontologists' training and experience upon the accuracy of their dental radiographic identifications. Forty participating odontologists with various levels of training and experience completed a Web-based survey of their qualifications and then completed nine Web-based radiographic identification cases. They made their identifications using the American Board of Forensic Odontology Categories and Terminology for Body Identification. The results indicate that odontologists with high levels of training and experience performed significantly more accurately than those with lower levels. We conclude that high levels of training and experience in forensic odontology should be developed, maintained, and required of dentists who participate in a forensic team dealing with challenging identification cases.     

The reliability of digitized radiographs for dental identification: a Web-based study

In the era of Daubert and other judicial rulings pertaining to the acceptability of forensic evidence, it is increasingly important that experts are able to testify that their methods have been scientifically tested and that error rates and other factors relating to reliability have been published. The purpose of this study was to determine the reliability of digitized radiographic comparisons for the purposes of dental identification. Participants with various forensic backgrounds and experience levels were passively recruited to the website. Ten forensic identification cases composed of antemortem and postmortem dental radiographs were supplied to examiners using a bespoke website. Participants responded to the cases on two occasions after a one-month washout interval using the ABFO conclusion levels for forensic identifications. A total of 115 first attempts and 87 matched second attempts were received. Of the total responses, 72% were dentally trained respondents who had completed at least one forensic identification case; of these, 38% were experienced forensic dentists who had completed more than 25 identifications. Data relating to accuracy, intra- and inter-examiner agreement, and the effect of case difficulty are presented. Mean accuracy was 85.5% for all cases, with the experienced forensic dentists obtaining a 91% success rate. The inter-examiner agreement on the negative identification cases was classified as poor. The data suggest that dental identifications resulting from the comparison of postmortem and antemortem radiographs are valid, accurate, and reliable when undertaken by experienced odontologists.     

Evaluation of dental radiographic identification: an experimental study

The object of this study was to assess the value of dental radiographs for the purposes of personal identification in the absence of tooth restorations. 198 periapical and bitewing radio graphs were taken of teeth contained in 22 dry skulls obtained from the skull collection of the Royal College of Surgeons of Edinburgh. Each selected view was taken three times: by a scientist, a dentist and a dental radiographer. Each operator independently positioned the films, selected the exposure times and positioned the cone of the X-ray machine. Three groups comprising forensic odontologists, dental vocational trainees and dental trainee hygienists attempted to match the randomly mixed radiographs into sets of three. Success rates for matching radio graphs ranged from 63.6 to 100%. The average for forensic odontologists was 93.3%, vocational trainees 85.2% and hygienists 89.7%. Where forensic odontologists had both formal training and experience, or extensive experience without formal training, the success rate was 100%. Where there was formal training but little experience the success rate was lower. Participants believed that root morphology and alignment had been the greatest aid to matching and not crown morphology. The depth of knowledge of the viewer correlated poorly with the number of correct results, although the forensic odontologists achieved the highest success rate. Formal training, although highly desirable, is no substitute for practical experience. Root morphology and alignment were cited most frequently as facilitating matching.     

Biomechanical Factors in Human Dermal Bitemarks in a Cadaver Model*

Abstract: In bitemark analysis, the forensic odontologist must consider how the biomechanical properties of the skin contribute to distortion of the bitemark. In addition, one must consider how the bitemark can be distorted by postural movement of the victim after the bite has occurred. A fundamental review of the architecture and biomechanical properties of the dermis is described and evaluated through bites made on cadavers. In order to assess distortion, 23 bites from a single characterized dentition were made on un‐embalmed cadaver skin. Bite indentations were photographed. Following various body manipulations they were re‐photographed in different positions. Hollow volume overlays of the biting dentition were constructed, and metric analysis of the dentition and all bitemarks was completed. The overall intercanine, mesial to distal, and angle of rotation distortion was calculated. Of the 23 bites made, none were measurably identical, and in some cases, dramatic distortion was noted.     

Dental participants in mass disasters--a retrospective study with future implications

Mass casualty incidents continue to require the services of forensic dentists to determine the identity of victims. Across North America and Europe. teams of forensic dentists train, using mock disaster exercises, to prepare for such duties. It is vital that these mock exercises simulate the features of real disaster situations as far as possible. In order to inform those responsible for the design and implementation of mock exercises, a study was undertaken to determine the features of actual disasters that dental personnel had attended. Using a questionnaire, data were solicited from 38 odontologists. The average number of disasters attended by the respondents was eight, with an average casualty number of 94. Aircraft crashes were the most frequent cause of disasters that were attended by the odontologists. The authors conclude that future mock disaster exercises should replicate features of aircraft crashes as closely as possible by using commingled, fragmented, and burned remains. In addition, mock disasters should require the identification of a realistic number of individuals to ensure authenticity and the maximum logistical preparedness of participants.     

Mathematical matching of a dentition to bitemarks: use and evaluation of affine methods

Skin is a less than ideal medium for recording bitemark impressions, and assessing the causes and magnitude of distortion has long been a question in forensic odontology. Affine methods have been suggested as a mathematical means to attempt to quantify the deformation typically seen with a bitemark. Thirty-six bites were created on unembalmed human cadavers with a single dentition. Three mathematical affine methods were evaluated to determine if the distortion could be described mathematically and effectively removed. A measure of mismatch of a dentition to a bitemark was developed based on landmark measurements establishing a numerical basis for comparisons of dentitions to bitemarks. Results indicate high levels of distortion in the bitemarks not attributable to affine deformations or measurement error, suggesting that non-uniform anisotropic properties of skin mostly contribute to the distortion seen, thus concluding that bitemark distortion cannot be corrected by using affine transformations.     

Forensic implications of biting behavior: a conceptually underdeveloped area of investigation

Within the context of a criminal investigation the human bitemark traditionally provides the forensic dentist with both physical and biological evidence. In recent years, however, examples exist where in addition to discussing physical and biological evidence, expert witnesses have also testified in court regarding the behavioral aspects of biting behavior. Interested in this additional source of evidence, the authors reviewed the research literature from which biting behavior could be explained. The review found a hiatus of empirical knowledge in this respect, with only two papers seemingly related to the topic. With this dearth of knowledge in mind, the authors present a framework for further analysis and tentatively suggest reasons for biting behaviors, using a range of psychological models. The article ends with a cautionary note that vague and often misleading behavioral assumptions must not be applied to bitemark testimony until further data are available.     

The emotional and psychological impact of mass casualty incidents on forensic odontologists

Motivated by the findings of a previous research project, 38 forensic odontologists with known occupational experience of mass casualty incidents completed a questionnaire designed to elicit both quantitative and qualitative data. The questionnaire sought to provide an insight into the psychological and emotional impact of conducting work of this nature. Two psychometric scales were included in the questionnaire, The Positive and Negative Affect scale (PANAS) and the Impact of Events Scale (IOE). In addition, a number of open-ended questions relating to the personal experiences of the respondent during the mass casualty incident were also included. Quantitative findings indicate that on the whole mass casualty incidents resulted in a positive experience for the respondents, although over a third reported being distressed, upset or irritable at some time during the event. Sense of achievement and camaraderie were among the qualitative themes elicited that help explain the positive reactions. Working conditions, politics and the ictims were cited as sources of negativity.     

The importance of forensic evidence for decisions on criminal guilt

Recent studies have found that the general public perceives forensic evidence to be relatively inaccurate and to involve high levels of human judgement. This study examines how important the general public finds forensic evidence by comparing decisions on guilt and punishment in criminal cases that involve forensic versus eyewitness testimony evidence and examining whether a CSI effect exists. Specifically, this experimental survey study utilized a 2 (crime type: murder or rape) × 4 (evidence type: DNA, fingerprint, victim eyewitness testimony, or bystander eyewitness testimony) ? 1 (no victim testimony for murder scenario) design, yielding seven vignettes scenarios to which participants were randomly assigned. Results indicate that forensic evidence was associated with more guilty verdicts and higher confidence in a guilty verdict. Forensic evidence did not change the expected sentence length and did not generally affect the ideal sentence length. However, for rape, respondents believed that the defendant should receive a longer sentence when forensic evidence was presented but forensic evidence did not alter likely sentence that respondents expected the defendant to receive. The results of this study did not support a CSI effect. Overall, this study suggests that forensic evidence – particularly DNA – has a stronger influence during the verdict stage than the sentencing stage.