Computer-based production of comparison overlays from 3D-scanned dental casts for bite mark analysis

Bite mark analysis assumes the uniqueness of the dentition can be accurately recorded on skin or an object. However, biting is a dynamic procedure involving three moving systems, the maxilla, the mandible, and the victim's reaction. Moreover, bite marks can be distorted by the anatomic location of the injury or the elasticity of the skin tissue. Therefore, the same dentition can produce bite marks that exhibit variations in appearance. The complexity of this source of evidence emphasizes the need for new 3D imaging technologies in bite mark analysis. This article presents a new software package, DentalPrint (2004, University of Granada, Department of Forensic Medicine and Forensic Odontology, Granada, Spain) that generates different comparison overlays from 3D dental cast images depending on the pressure of the bite or the distortion caused by victim-biter interaction. The procedure for generating comparison overlays is entirely automatic, thus avoiding observer bias. Moreover, the software presented here makes it impossible for third parties to manipulate or alter the 3D images, making DentalPrint suitable for bite mark analyses to be used in court proceedings.     

Lack of dental uniqueness between two bite mark suspects.

The central dogma of bite mark analysis is based upon two assumptions. The first is that human teeth are unique, and the second is that sufficient detail of the uniqueness is rendered during the biting process to enable identification. Both of these assumptions have been challenged over recent years, and a healthy scientific skepticism surrounding bite mark analysis has developed. The case presented features two suspects whose dental arrangement was similar and, when compared to the bite mark, both demonstrated consistent features. Within a closed population of possible biters, one of the two suspects was responsible for the injury. The case is illustrated with photographic and overlay detail of the suspect's teeth and demonstrates the complexity of such cases. The authors call for greater caution when drawing conclusions from such cases and highlight the need for further research into the replication of dental features on human skin.     

Photographic evidence protocol: the use of digital imaging methods to rectify angular distortion and create life size reproductions of bite mark evidence

Bite mark evidence seen in skin injuries or objects is commonly photographed for evidentiary documentation, preservation, and analysis. Distortion in forensic evidence photographs diminishes the outcome of analytical procedures available to the forensic odontologist. Inaccurate positioning of the evidence, camera, or measurement reference scale creates perspective and parallax distortion of the captured image. These variables must be eliminated, if possible, to ensure reliable results derived from comparison of the suspect teeth and the bite mark. Detection and measurement of camera/evidence/scale misalignment is the threshold step in evidence evaluation, and is possible through digital imaging methods coupled with established methods. Correction (rectification) of perspective distortion is possible through the application of additional digital editing techniques. This study establishes type categories of perspective and parallax distortion seen in bite mark evidence, validates the use of the digital imaging tools of Adobe Photoshop to correct certain types of distortion, and establishes a forensic protocol to verify the accuracy of evidence photographs requiring dimensional accuracy.     

咬痕个体识别的比对方法

目的 建立一个牙模数据库,为通过牙齿、咬痕进行个人识别的研究及其在法医实践中的应用提供一种新方法。方法 经过对400例牙模进行分析、计算,将牙齿的形状、排列转换成数字型(X,Y)坐标,通过计算出每颗牙关键点与坐标原点的相对位置,在DOS系统下运用Borland C++5.0语言编写程序,快速地计算出牙齿和牙弓的特征。结果 能对牙模进行自动识别,达到排除与认定。其比对精度长度为1.3mm,角度3°;可取的最少牙点位数目为12～14较为合理,大致需要5～7个完整的牙痕。结论 该方法是研究咬痕与牙模比对的基础。     

A framework for estimating probability of a match in forensic bite mark identification

In forensic dentistry, a human expert typically does the comparison and identification based on bite marks. Unlike DNA analysis, however, there is no quantitative basis with which to assign a probability for this given match. This paper proposes a framework for empirically estimating the probability of such a bite mark match and reports on initial experimental results. The methodology involved collection of dental population data (3D dental casts and bite mark images), image analysis for quantitatively measuring the degree of match (based on chamfer distance), and performing a logistic regression analysis using the collected population data to estimate the probability of match from the calculated degree of match. The model correctly predicted 35 of the 42 matches and 585 of the 588 mismatches. The method also has potential for use in other forensic applications in which the assignment of quantitative probabilities is important.     

Optical 3D surface digitizing in forensic medicine: 3D documentation of skin and bone injuries

Photography process reduces a three-dimensional (3D) wound to a two-dimensional level. If there is a need for a high-resolution 3D dataset of an object, it needs to be three-dimensionally scanned. No-contact optical 3D digitizing surface scanners can be used as a powerful tool for wound and injury-causing instrument analysis in trauma cases. The 3D skin wound and a bone injury documentation using the optical scanner Advanced TOpometric Sensor (ATOS II, GOM International, Switzerland) will be demonstrated using two illustrative cases. Using this 3D optical digitizing method the wounds (the virtual 3D computer model of the skin and the bone injuries) and the virtual 3D model of the injury-causing tool are graphically documented in 3D in real-life size and shape and can be rotated in the CAD program on the computer screen. In addition, the virtual 3D models of the bone injuries and tool can now be compared in a 3D CAD program against one another in virtual space, to see if there are matching areas. Further steps in forensic medicine will be a full 3D surface documentation of the human body and all the forensic relevant injuries using optical 3D scanners.     

Experimental Study of Bite Mark Injuries by Digital Analysis

Abstract: This study was based on a morphometric analysis of bite marks starting from the quantitative definition of the anterior teeth by the geometric acquisition of the “injuries,” using bite marks impressed on pig skin and plastic. Each mark was photographed and acquired. A dedicated program automatically supplied the values of the shape factors and the areas of the pattern geometric figures. The values obtained for the homologous samples were compared to the heterologous values. Statistical comparison was made of the sets by linear regression, determining the correlation coefficient and the determination coefficient for each value. Results showed only 4.8% and 2% of overlap between homologous and heterologous values. This study was carried out in attempting to quantitatively define the anterior teeth of the human dentition and the procedure described and the results obtained support the advantage of morphometric studies and computer‐aided programs in this study of bite marks.     

Not all bite marks are associated with abuse, sexual activities, or homicides: a case study of a self-inflicted bite mark

A case of self-inflicted bite mark during an episode of myocardial ischemia is presented. Using current bite mark identification techniques, the bite mark was shown to be self-inflicted. Self-biting may be an emotional response to pain or a type of counterirritation to alleviate pain. The recognition and documentation of this unusual case of a self-inflicted bite mark was due to the cooperation of the forensic pathologist and forensic odontologist.     

Bite Mark Analysis in Foodstuffs and Inanimate Objects and the Underlying Proofs for Validity and Judicial Acceptance

Even though one of the first bite mark cases was Doyle v. State in 1954 (a bitten cheese case), the research has focused on bite marks inflicted in human skin. As published Papers, Case Reports, or Technical Notes can constitute precedents which are relied upon in making the legal arguments and a considerable amount of case law exists in this area, we present a systematic review on bite mark analysis in foodstuffs and inanimate objects and their underlying proofs for validity and judicial acceptance according to Daubert rulings. Results showed that there is vulnerability in these procedures, and it is essential to demand for focus scrutiny on the known error rates when such evidence is presented in trials. These kinds of bite marks are well documented; however, there has been little research in this field knowing that the protocols of analysis and comparison are the responsibility of the forensic odontologists.     

Analysis of salivary DNA evidence from a bite mark on a body submerged in water.

A female body was recovered after approximately 5.5 h in a river with slow-moving current. On the victim's right breast, a patterned injury was discovered and determined to be from human adult teeth. Evidence was collected according to established techniques including recovery of saliva from the bite mark area despite the body being found submerged in water. DNA analysis by PCR using polymorphic STR markers revealed a DNA profile of mixed origin. In addition to the victim's DNA profile, a genotype contribution from the perpetrator was identified as a minor component. The DNA typing results from the bite mark correlated with the DNA typing results obtained from other biological trace evidence identified from the victim's genital samples. The bite mark and the DNA evidence were used to screen suspects and played an important role in obtaining resolution of this case. Consequently, it is advisable that investigators routinely swab for salivary DNA in bite mark cases, even when the amount is thought to be minimal.     

Assignment of a bite-mark on the victim's skin to the dentition of the perpetrator by means of anomalies in the number and position of the frontal teeth

This report is about a bite mark on the breast of a female corpse. The woman had been killed by ligature strangulation at the age of 76 years. The investigation of the dental casts of a suspected man showed some anomalies in the dentition and orthodontic variations. A comparison of the bite mark with these anomalies demonstrated the correspondence of several details. Consequently, the probability that the suspect was responsible for the bite mark was regarded as being very high. During the further investigations the suspect admitted the offence including the bite injury to the breast. The authors emphasize the importance of an exact photographic documentation as an indispensable prerequisite for an odontological comparison.     

Measurement of arch widths in a human population: relation of anticipated bite marks

The authors compared arch width measurements of diagnostic dental models obtained from dental school patients. Arch width measurements were taken in the canine area on each dental cast in an effort to assist forensic dental investigators in matching certain classes of subjects to the bites they might possibly inflict. If any canine teeth were absent, the measurements were taken using other specified adjacent teeth which the investigators felt would be interpreted as the arch width determiners in a bite mark injury. The ages of the subjects varied from 14 to 87 years. Statistical comparison of the maxillary arch width, mandibular arch width, and the mean difference between maxillary and mandibular arch width were performed. Significant differences between the arch width measurements were found to exist between several classes of subjects based on race and sex.     

A survey of the incidence of missing anterior teeth: potential value in bite mark analysis.

Bite mark analysis involves comparison of individual dental characteristics between a dentition and the bite injury. A bite mark injury may result from sexual assault, or physical assault, and defensive injuries, and as such can be used to link a suspect to a victim or vice versa. Missing teeth are one of the characteristics that could implicate or exclude a suspected biter. However frequency data for use by forensic odontologists can only be collated from epidemiological studies. Therefore an audit was undertaken of missing anterior teeth in adult patients (n = 1010) attending for treatment, gathering data that could be more relevant to odontology. One in five of the sample presented with missing teeth that were either replaced with a denture (11%), not replaced (6%) or missing with the gap closed (2%).     

Use of an acrylonitrile-butadiene-styrene (ABS) plastic ring as a matrix in the recovery of bite mark evidence

Valuable forensic information can be obtained from analysis of human bite mark injuries after careful retrieval of such evidence from living or deceased victims. It is difficult, however, to maintain the anatomical configuration of the skin, especially where body contours complicate the recovery process. Transillumination of the injury pattern in the skin after removal and preservation of the tissue from a deceased victim can provide significant information in the investigation process. A dimensionally stable matrix is required to support the skin's anatomical configuration during and after its removal. The authors have developed a unique and convenient method of heating and contouring a ring of acrylonitrile-butadiene-styrene (ABS) plastic using table salt over a heat source. When this ring is applied to the deceased victim's skin, and a backing material is added for support, removal of the skin and the bite mark can be accomplished more predictably while maintaining the anatomical contour. It is important to record bite marks accurately as soon after discovery as possible; the authors believe that this technique will significantly aid recovery of such evidence either at the crime scene or in the laboratory. A method of inscribing appropriate anatomical markers and case numbers on the rings is also described.     

The use of human skin in the fabrication of a bite mark template: two case reports

Comparison of a suspected biter's dental arches with the patterned injury of a bite mark is especially difficult when the bite occurs in an anatomic location with a small radius of curvature or with complex or compound curves. The authors present two case reports in which human skin was used as a template for the reproduction of a bite. In one case the victim's skin was used; in the other, the skin of a anatomically similar person was used. The use of inked dental casts, photography, and transparent overlays significantly reduced the errors common to analysis of bite marks in these highly curved areas.     

Toneline bite mark photography.

In bite mark analyses, the initial photograph is critical for the collection and presentation of evidence. A high-contrast film technique previously used primarily in the graphic arts field has been refined and applied to forensic odontology. The process, called toneline, reduces the interpretational bias of the investigator and yields a transparent overlay with a photographic outline of the bite mark which can be directly compared with models of the suspect's teeth.     

Analysis of distortion in preserved bite mark skin

In addition to other methods for conservation of bite mark evidence, preservation of actual skin from deceased victims is often suggested. This study was undertaken to analyze the dimensional stability of such specimens. Utilizing a prefabricated template, marks approximating "bites" were made in postmortem skin of Miniature Hanford pigs, producing imprints with distinct margins and indentations. Tissue samples were stored in 10% formalin after affixing an acrylic support ring with cyanoacrylate adhesive and sutures. Measurements of the six tooth mark analogues and cross-arch dimensions were taken at intervals of up to 38 days. Data from these measurements indicate a wide range of amount and type of distortion in preserved tissue. Although some samples were dimensionally stable, there was both contraction and expansion of bite mark specimens, even within individual skin samples. It appears that standard techniques for storage and preservation of bite mark samples will not produce reliable dimensional accuracy.     

A forensic classification of distortion in human bite marks

The occurrence of distortion in human bite marks is well recognised. A forensic classification of distortion is suggested which is based upon the causative factors and their inter-relationships. The terms primary distortion and secondary distortion are introduced and described. The objective of this classification is to emphasise the need for a scientific approach to the recognition and interpretation of the types of distortion found in human bite marks. The relationships between distortion, distinctive features and superimposition techniques in bite mark analysis are discussed.     

National survey of the incidence of missing anterior teeth: Potential use in bite mark analysis in the Brazilian context

Bite mark analysis in forensic dentistry presupposes that the human dentition is unique and that its characteristics can be transferred precisely to several materials. The aim of the present study was to register the frequency of missing anterior teeth in the Brazilian adult population, discussing its potential importance in bite mark analysis. Data from the Brazilian Oral Health Survey were used; 13,431 male and female individuals aged 35 to 44 were examined according to the criteria of the World Health Organization. The analysis of Poisson regression was performed in order to calculate the rating ratios and the respective confidence interval at 95%. A total of 13,431 adults participated in the study. Among male individuals, 2063 (47.00%) were dentate and 2036 (46.40%) had at least one missing tooth. Only 254 (5.83%) were totally edentulous. A significant number of males and females presented 6 missing teeth in the same dental arch, revealing the poor state of oral health of adult Brazilians. Missing teeth were more frequent in the upper dental arch than in the lower arch. In the upper dental arch, the incisor group (central and lateral) was missing the most. In the lower dental arch, however, a certain lack of homogeneity was observed among the different dental groups as regards missing teeth. White individuals presented a smaller proportion of missing teeth compared to the other ethnic groups. Females were 1.61 (CI 1.50–1.73) times more likely than males to present missing teeth. The absence of upper teeth and the presence of lower teeth were observed in 16.10% of the individuals. Further research should also include an analysis of different age groups. This would increase the potential of applying this kind of information to bite mark analysis.