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.     

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.     

A study of multiple bitemarks inflicted in human skin by a single dentition using geometric morphometric analysis

Criticisms of the forensic discipline of bitemark analysis state that the range of distortion in the shape of bitemark impressions in skin has not been scientifically established. No systematic statistical studies exist that explore this problem. As a preliminary investigation of this issue, a single dentition was mounted in a mechanical apparatus and used to create 89 bitemarks in human cadaver skin, both parallel and perpendicular to tension lines. Impressions of the same dentition were also created in wax. 2D scanned images of the biting dentition were obtained. Locations of incisal edges of all 6 anterior teeth as well as the midpoint of the canine were captured as landmarks in all specimens. This set of landmark data was then studied using established geometric morphometric methods. All specimen shapes were compared using Procrustes superimposition methods, and by a variation of Procrustes superimposition which preserves scale information. Match criteria were established by examining the range of variation produced by repeated measurements of the dentition for each class of specimen. The bitemarks were also compared to a population of 411 digitally scanned dentitions, again using the match criteria. Results showed that bitemarks in wax had lower measurement error than scanned images of the dentition, and both were substantially lower than measurement error as recorded in skin. None of the 89 bitemarks matched the measured shape of the biting dentition or bitemarks in wax, within the repeated measurements error level, despite the fact that all bitemarks were produced by this dentition. Comparison of the bitemarks to the collection of 411 dentitions showed that the closest match to the bitemarks was not always the same dentition that produced the bitemarks. Examination of Procrustes plots of matched shapes showed non-overlapping distributions of measurements of bitemarks in skin, wax, and the dentition. All had statistically significant differences in mean shape. Principal component analysis (PCA) and canonical variates analysis (CVA) both showed clear segregation of the three types of data. The patterns of variance revealed by PCA showed several distinct patterns produced by skin distortion; alteration of relative arch width, and varying displacement of non-aligned teeth in the dentition. These initial results indicate that when multiple suspects possess similar dentitions, bitemark analysis should be approached with caution.     

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.     

The Response of Skin to Applied Stress: Investigation of Bitemark Distortion in a Cadaver Model*

Abstract: Knowledge of distortional properties of skin is important in bitemark analysis. Thus, the response of skin to stress from bites was investigated. Four sets of models were created from the dentition of one individual. Anterior teeth were systematically removed to vary contact surface area. A biting apparatus was constructed with an integrated load cell. Forty‐six bites were created perpendicular to Langer lines on six cadavers. Rate of force application and bite pressure were controlled. Metric/angular measurement and hollow volume overlays were employed. Distortion produced by each dentition was calculated and assessed. Results showed that as teeth impressed loose tissue, mesial/distal distance increased, angles of rotation flattened, and inter‐canine distance lengthened. An opposite effect was seen in tight tissue. When the surface area of the dentition was reduced, a mixture of these effects was observed. Conclusions indicated that stiffness of the tissue was the most important variable in bitemark distortion.     

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.     

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.     

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.     

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.     

人牙咬痕形态学变化动态过程研究

目的　研究人牙咬痕形态学变化的动态过程 ,了解咬痕发生、发展的变化规律 ,为已发生变化的咬痕同一认定提供依据。方法　动态追踪观察活体及死亡动物咬痕的变化过程 ,并测定其相关形态参数 ,多元逐步回归分析咬痕形态、牙面积、时间、牙合力、牙宽度、牙厚度之间的关系 ,建立咬痕形态学变化回归方程。结果　咬痕的形态、牙形态、时间、牙合力有一定的数学关系 :S =-6 96-1 68× 10 2 T -0 11F +2 2 1W +3 75H (活体狗实验T <3 60min) ;S =-2 1 90 +5 3 4× 10 2 T -0 3 6F +4 5 7W +6 66H (死亡狗实验T <14 40min)。     

A web-based survey of odontologist's opinions concerning bitemark analyses

Within the field of forensic dentistry, the detection, collection, and analysis of bitemarks remains one of the most contentious areas. Attempts at the production of consensus documents have produced documents such as the ABFO's Guidelines for Bitemark Evidence Collection. Despite this, the range of differing analysis techniques, allied with a varied opinion base on the robustness of bitemark conclusions has led to polarized views within the profession. The purpose of this study was to survey forensic dentists to obtain their views on a number of crucial components of bitemark theory and contentious areas within the discipline. Using a web-based survey, 14 questions were asked of respondents. Seventy-two odontologists completed the survey, with 38% being of Diplomate status, 10% had completed 20 or more bitemark cases, and 20% between 10 and 20 cases, 91% of respondents believed that the human dentition was unique, with 78% believing that this uniqueness could be represented on human skin during the biting process. Seventy percent believed that they could positively identify an individual from a bitemark, and 22% stated that the statistical tool, the product rule, should be applied to bitemark conclusions. Over half of the odontologists used overlays for bitemark analysis. with a digital method of production the most popular. The implications of these and other findings are discussed.     

Statistical Evidence for the Similarity of the Human Dentition

Abstract: Recent scrutiny of forensic science has focused on unreliability of expert witness testimony when based on statements of individuality. In bitemark analysis, assumptions regarding uniqueness of the dentition have been based on use of the product rule while ignoring correlation and nonuniformity of dental arrangement. To examine the effect of these factors, two separate sets of scanned dental models (n = 172 and n = 344) were measured and statistically tested to determine match rates. Results were compared to those of a prior study. Seven and 16 matches of the six anterior lower teeth were found in the respective data sets. Correlations and nonuniform distributions of tooth positions were observed. Simulation tests were performed to verify results. Results indicate that given experimental measurement parameters, statements of dental uniqueness with respect to bitemark analysis in an open population are unsupportable and that use of the product rule is inappropriate.     

Bite marks: physical properties of ring adhesion to skin--phase 2

Abstract: Bite Marks: This study demonstrated that surface wetness was the most influential factor affecting ring adhesion to skin. Also, chemical depilatories and shaving creams were to be avoided when cleaning the skin. The second phase of this research examines the tensile stress needed to rupture the bond between TAK^® hydroplastic, three new cyanoacrylates, and pigskin with particular consideration for temperature variations. This study also considers solubility issues of different cyanoacrylates in 10% formalin. Finally, the Dorion Type V bitemark excision technique could significantly reduce the risks of tissue distortion when used in conjunction with the following methods and materials. The skin should be devoid of moisture, razor shaved, and cleaned with dishwashing detergent and 98.9% ethanol while avoiding the use of shaving creams and/or chemical depilatories where ring placement is anticipated. The use of unopened cyanoacrylate is encouraged with Permabond^® as the cyanoacrylate of choice.     

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.     

Old dogs can learn new tricks--a new application of the ABFO #2 scale

In 1984 at its first Bitemark Workshop, the American Board of Forensic Odontology (ABFO) developed guidelines for the analysis of bitemark evidence. Prior to this, no standards had been established for the evaluation of bitemarks. The development of the ABFO #2 scale in 1987 gave the forensic odontologist a reproducible way to rectify and measure bitemarks that had been documented photographically. Primarily developed for the analysis of bitemark evidence, its use has expanded to encompass myriad forms of evidence. While the ABFO #2 scale can depict horizontal and vertical measurements, it is unable to depict depth accurately. The purpose of this paper is to show its successful application to three dimensions.     

Uniqueness of the Dentition as Impressed in Human Skin: A Cadaver Model*

Abstract: Bitemark interpretation assumes that the human dentition is unique and that its attributes can be accurately transferred to skin. A cadaver model was used to investigate whether the correct biter could be determined from similarly aligned dentitions once the dentitions were impressed in human skin. One‐hundred dental stone models, which were measured and determined to be unique, were divided into 10 groups based upon similarities of mal‐alignment patterns. One model was randomly selected from each group and bites were produced on unembalmed human cadavers. Metric/angular measurements and hollow volume overlays of the models were compared with the bites made. The percentage of dentitions from each group as well as the 100 dental model population that could not be excluded as the biter was determined. Results showed difficulty distinguishing the biter from individuals with similarly aligned dentitions and in some cases, an incorrect biter appeared better correlated to the bite.     

Digital analysis of experimental human bitemarks: application of two new methods

Bitemark determination in forensic odontology is commonly performed by comparing the morphology of the dentition of the suspect with life-sized photographs of injury on the victim's skin using transparent overlays or computers. The purpose of this study is to investigate the suitability of two new different methods for identification of bitemarks by digital analysis. A sample of 50 volunteers was asked to make experimental bitemarks on the arms of each other. Stone study casts were prepared from upper and lower dental arches of each volunteer. The bitemarks and the study casts were photographed; the photos were entered into the computer and Adobe Photoshop software program was applied to analyze the results. Two methods (2D polyline and Painting) of identification were used. In the 2D polyline method, fixed points were chosen on the tips of the canines and a straight line was drawn between the two fixed points in the arch (intercanine line). Straight lines passing between the incisal edges of the incisors were drawn vertically on the intercanine line; the lines and angles created were calculated. In the painting method, identification was based on canine-to-canine distance, tooth width and the thickness, and rotational value of each tooth. The results showed that both methods were applicable. However, the 2D polyline method was more convenient to use and gave prompt computer-read results, whereas the painting method depended on the visual reading of the operator.     

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.     

Patterns of Variation and Match Rates of the Anterior Biting Dentition: Characteristics of a Database of 3D‐Scanned Dentitions

An understanding of the variability of the anterior human dentition is essential in bitemark analysis. A collection of 1099 3D laser scans of paired maxillary and mandibular arches were studied using geometric morphometric methods. Analyses were performed without scale (shape only) and with scale (shape and size). Specimens differing by no more than experimentally obtained measurement error were counted as matches, or as indistinguishable. A total of 487 maxillary (396 size preserved), 131 mandibular (83 size preserved), and one paired dentition (two size preserved) matches were found. Principal component analysis and partial least squares revealed interpretable patterns of variation and covariation in dental shape, principally dominated by variation in dental arch width. The sensitivity of match rate to assumed degree of measurement error was also determined showing rapid increases in match rate as measurement error increased. In conclusion, the concept of dental uniqueness with regard to bitemark analysis should be approached with caution.     

Dental shape match rates in selected and orthodontically treated populations in New York State: a two-dimensional study

Forensically identifying a suspect's dentition from a bitemark in an open population requires the supposition that every person's dental alignment is different. There have been few studies that have tested this claim. Four hundred and ten lower anterior dentitions from a selected population and 110 lower anterior dentitions from one that was orthodontically treated were measured using geometric morphometric analysis, allowing comparison of arch shape. Dental match rates of 1.46% and 42.7% of individuals were found in the respective populations, given an established measurement error. Orthodontic treatment had a strong effect on match rate suggesting that treated or naturally well-aligned dentitions may be indistinguishable. Sexual dimorphism was found to be only slightly significant. Principal shape variation in both populations was degree of arch curvature. Results of studying these populations show that dental matches can occur, and that statements of certainty concerning individualization in such populations should be approached with caution.