Forensic dentistry

Forensic dentistry or forensic odontology is the proper handling, examination and evaluation of dental evidence, which will be then presented in the interest of justice. The evidence that may be derived from teeth, is the age (in children) and identification of the person to whom the teeth belong. This is done using dental records or ante-mortem (prior to death) photographs. Forensic odontology is derived from latin, meaning forum or where legal matters are discussed. The first forensic dentist in the United States was Dr. Paul Revere who was known for the identification of fallen revolutionary soldiers.

The other type of evidence is that of bite marks, left on either the victim (by the attacker), the perpetrator (from the victim of an attack), or on an object found at the crime scene. Bite marks are often found on children who are abused.

Forensic dentists are responsible for six main areas of practice:


 * Identification of found human remains
 * Identification in mass fatalities
 * Assessment of bite mark injuries
 * Assessment of cases of abuse (child, spousal, elder)
 * Civil cases involving malpractice
 * Age estimation

Background
Forensic odontology is the study of dental applications in legal proceedings. The subject covers a wide variety of topics including individual identification, mass identification, and bite mark analysis. The study of odontology in a legal case can be a piece of incriminating evidence or an aspect of wide controversy.

There have been many cases throughout history which have made use of bite marks as evidence. Bite marks are usually seen in cases involving sexual assault, murder, and child abuse and can be a major factor in leading to a conviction. Biting is often a sign of the perpetrator seeking to degrade the victim while also achieving complete domination.

Bite marks can be found anywhere on a body, particularly on soft, fleshy tissue such as the stomach or buttocks. In addition, bite marks can be found on objects present at the scene of a crime. Bite marks are commonly found on a suspect when a victim attempts to defend him/herself.

Even though using bite mark evidence began around 1870, the first published account involving a conviction based on bite marks as evidence was in the case of Doyle v. State, which occurred in Texas in 1954. The bite mark in this case was on a piece of cheese found at the crime scene of a burglary. The defendant was later asked to bite another piece of cheese for comparison. A firearms examiner and a dentist evaluated the bite marks independently and both concluded that the marks were made by the same set of teeth. The conviction in this case set the stage for bite marks found on objects and skin to be used as evidence in future cases.

Another landmark case was People v. Marx, which occurred in California in 1975. A woman was murdered by strangulation after being sexually assaulted. She was bitten several times on her nose. Walter Marx was identified as a suspect and dental impressions were made of his teeth. Impressions and photographs were also taken of the woman’s injured nose. These samples along with other models and casts were evaluated using a variety of techniques, including two-dimensional and three-dimensional comparisons, and acetate overlays. Three experts testified that the bite marks on the woman’s nose were indeed made by Marx and he was convicted of voluntary manslaughter.

High-profile criminal cases
Forensic odontology has played a key role in famous criminal cases:
 * State of Florida v. Ted Bundy
 * State of New Jersey v. Jesse Timmendequas (Megan's Law case)
 * People of California v. Marx, the 1975 case which established evidentiary standards for forensic odontology
 * People of Arizona v. Ray Krone, bite mark evidence led to a wrongful conviction.

Organizations
Three organizations are dedicated to the field of forensic odontology. These organizations include: the Bureau of Legal Dentistry (BOLD), the American Board of Forensic Odontology (ABFO), and the International Organization for Forensic Odonto-Stomatology (IOFOS). In 1996, BOLD was created at the University of British Columbia to develop new technology and techniques in forensic odontology. The University of British Columbia program is the only one in North America that provides graduate training in forensic odontology.

The Bureau of Legal Dentistry encourages the use of multiple dental impressions to create a “dental lineup”, similar to a suspect lineup used to identify alleged perpetrators of crime. Currently, dental impressions collected as evidence are compared only to those collected from a given suspect, which may bias the resulting outcome. Using multiple dental impressions in a lineup may enable forensic odontologists to significantly decrease the current bias in matching bite marks to the teeth of a suspect. The organization BOLD also supports the creation of a database of dental records, which could help in verifying dental uniqueness. This database could be created using criminal records or possibly all dental patients.

In 1984, the ABFO began making an attempt to diminish the discrepancies and increase the validity of bite mark analysis by creating bite mark methodology guidelines. The guidelines attempt to establish standard terminology in describing bite marks and that reduces the risk of biased results. The ABFO also provides advice on how to effectively collect and preserve evidence. For example, they recommend that the collection of DNA evidence and detailed photographs of bites be taken together at the crime scene. The guidelines also outline how and what a forensic odontologist should record, such as the location, contours, shape, and size of a bite mark. They also provide a system of scoring to assess the degree to which a suspect’s dental profile and bite mark match. According to the ABFO, the guidelines are not a mandate of methods to be used, but a list of generally accepted methods. The guidelines are intended to prevent potentially useful evidence from being thrown out simply because the forensic odontologist’s collection methods were not standardized.

Kouble and Craig used a simplified version of the ABFO scoring guidelines in order to retain accuracy with a larger sample of comparisons. A numerical score was assigned to represent the degree of similarity between the bite mark and model/overlay. The higher the score, the greater the similarity. In order to simplify the model, some features that were individually scored in the ABFO guidelines such as arch size and shape were assessed together while certain distinctive features such as spacing between teeth were treated as a separate variable. The authors believe that a simplified version would increase the strength of the comparison process. In an attempt to improve guidelines used to collect dental evidence, IOFOS developed one of the most recognized systems for the collection of forensic dental evidence

Bite Mark Analysis
Upon collection of dental evidence, the forensic odontologist analyzes and compares the bite marks. Studies have been performed in an attempt to find the simplest, most efficient, and most reliable way of analyzing bite marks. Factors that may affect the accuracy of bite mark identification include time-dependant changes of the bite mark on living bodies, effects of where the bite mark was found, damage on soft tissue, and similarities in dentition among individuals. Other factors include poor photography, impressions, or measurement of dentition characteristics.

Most bite mark analysis studies use porcine skin (pigskin) since it is comparable to the skin of a human because it is considered unethical to bite a human for study in the United States. Limitations to the bite mark studies include differences in properties of pigskin compared to human skin and the technique of using simulated pressures to create bite marks. Although similar histologically, pigskin and human skin behave in dynamically different ways due to differences in elasticity. Furthermore, postmortem bites on nonhuman skin, such as those used in the experiments of Martin-de-las Heras et al., display different patterns to those seen in antemortem bite injuries. In recognition of the limitations of their study, Kouble and Craig suggest using a G-clamp on an articulator in future studies to standardize the amount of pressure used to produce experimental bite marks instead of applying manual pressure to models on pigskin. Future research and technological developments may help reduce the occurrence of such limitations.

Kouble and Craig compared direct methods and indirect methods of bite mark analysis. In the past, the direct method compared a model of the suspect’s teeth to a life-size photograph of the actual bite mark. In these experiments, direct comparisons were made between dental models and either photographs or “fingerprint powder lift-models.” The “fingerprint powder lift” technique involves dusting the bitten skin with black fingerprint powder and using fingerprint tape to transfer the bite marks onto a sheet of acetate.

Indirect methods involve the use of transparent overlays to record a suspect’s biting edges. Transparent overlays are made by free-hand tracing the occlusal surfaces of a dental model onto an acetate sheet. When comparing the “fingerprint powder lift” technique against the photographs, the use of photographs resulted in higher scores determined by a modified version of the ABFO scoring guidelines. The use of transparent overlays is considered subjective and irreproducible because the tracing can be easily manipulated. On the other hand, photocopier-generated overlays where no tracing is used is considered to be the best method in matching the correct bite mark to the correct set of models without the use of computer imaging.

While the photocopier-generated technique is sensitive, reliable, and inexpensive, new methods involving digital overlays have proven to be more accurate. Two recent technological developments include the 2D polyline method and the painting method. Both methods use Adobe® Photoshop®. Use of the 2D polyline method entails drawing straight lines between two fixed points in the arch and between incisal edges to indicate the tooth width. Use of the painting method entails coating the incisal edges of a dental model with red glossy paint and then photographing the model. Adobe® Photoshop® is then used to make measurements on the image. A total of 13 variables were used in analysis. Identification for both methods were based on canine-to-canine distance (1 variable), incisor width (4 variables), and rotational angles of the incisors (8 variables). The 2D polyline method relies heavily on accurate measurements, while the painting method depends on precise overlaying of the images. Although both methods were reliable, the 2D polyline method gave efficient and more objective results.

The latest indirect analysis method uses DentalPrint© which generates biting edges to compare overlays from 3-dimensional images of a dental cast to those generated from Adobe® Photoshop®. Martin-de las Heras et al. suggests using this method to identify negative dentitions. The purpose of this study was to make a comparison between DentalPrint© and Adobe® Photoshop® and to determine the impact of an examiner’s experience in influencing the accuracy of results.

Use of the DentalPrint© method involves three stages. First, the teeth involved in the bite mark are identified. Next, a contact plane is created from the three highest points detected in the 3-dimensional image of the dental cast. Lastly, DentalPrint© software is used to extend the contact plane deep into the teeth to acquire all biting edges of the cast. In a blind trial, an expert and a non-expert were asked to make comparisons (n=128). Martin-de las Heras et al. found that experienced examiners performed significantly better than non-experts when using either DentalPrint© software or Adobe® Photoshop® software in correctly identifying the biter.

Criticism
Recently, the scientific foundation of forensic odontology, and especially bite mark comparison, has been called into question. A 1999 study by a member of the Board of Forensic Odontology] found a 63 percent rate of false identifications. An investigative series by the Chicago Tribune entitled "Forensics under the Microscope" examined many forensic science disciplines to see if they truly deserve the air of infallibility that has come to surround them. The investigators concluded that bite mark comparison is always subjective and no standards for comparison have been accepted across the field. The journalists discovered that no rigorous experimentation has been conducted to determine error rates for bite mark comparison, a key part of the scientific method. Critics of bite mark comparison cite the case of Ray Krone, an Arizona man convicted of murder on bite mark evidence left on a woman's breast. DNA evidence later implicated another man and Krone was released from prison. Similarly, Roy Brown was convicted of murder due in part to bite-mark evidence, and freed after DNA testing of the saliva left in the bite wounds matched someone else.

Although bite mark analysis has been used in legal proceedings since 1870, it remains a controversial topic due to a variety of factors. DeVore and Barbenel and Evans have shown that the accuracy of a bite mark on skin is limited at best. Skin is not a good medium for dental impressions; it is liable to have a number of irregularities present before the imprint that could cause distortion. Also, bite marks can be altered through stretching, movement or a changing environment during and after the actual bite. Furthermore, the level of distortion tends to increase after the bite mark was made. Both studies suggest that for the bite mark to be accurately analyzed, the body must be examined in exactly the same position it was in when the bite occurred which can be a difficult if not an impossible task to accomplish. Bite mark distortion can rarely be quantified. Therefore, bite marks found at the scene are often analyzed under the assumption that they have undergone minimal distortion. Only limited research has been done in trying to quantify the level of distortion of a bite mark on human skin since the 1970s. The lack of research may largely be due to the fact that such studies are difficult to organize and are very expensive.

Bite mark analysis is also controversial because dental profiles are subject to change. The loss of teeth or the alteration of arch configuration through a variety of procedures is common in human populations. The onset of oral diseases such as dental caries has been shown to alter the arch and tooth configuration and must be taken into account when comparing a dental profile to the bite mark after a significant amount of time has passed since the mark was made.

While the methods behind collecting bite mark evidence at the scene are leading toward greater standardization, the methodology behind analyzing bite marks is extremely variable because it depends upon the preference of the specific odontologist. As discussed earlier, there are several methods used to compare bite marks ranging from life sized photographs to computer enhanced 3-dimensional imaging. These methods vary in precision and accuracy, and there is no set standard by which to compare or analyze them. The lack of analytical standards leads to a wide array of interpretation with any bite mark evidence. Some odontologists even disagree on whether or not a mark on the body is the result of a bite. Therefore, the interpretation of evidence lies largely on the expertise of the forensic odontologist handling the case.

One possible issue facing bite mark analysis is a lack of bite mark uniqueness in any given population. Bite mark analysis is based on the assumptions that the dental characteristics of anterior teeth involved in biting are unique amongst individuals, and this asserted uniqueness is transferred and recorded in the injury. However, there is very little reliable research to support these assumptions. A study performed by MacFarlane et al. supported the notion of dental uniqueness, but the study revolved around the visual assessment of a cast as opposed to the bite mark that could have been produced by the cast. In another study conducted by Sognnaes et al., the group tried to find uniqueness between the dental profiles of identical twins in an attempt to prove dental uniqueness in the general population. However, this study suffered from a small sample size (n=5), with the intent to extrapolate the data to the general population. They also used plaster of paris as the substrate to simulate skin, yet the two materials have very different properties. In a review conducted by Strom, he references a study conducted by Berg and Schaidt which suggested that at least four to five teeth need to be present in the mark to ensure its uniqueness and make a positive identification. However, this study was done long before many of the current evaluation methods, and this sheds doubt on how applicable these conclusions are today.

One of the most well known papers attempting to provide empirical data on bite mark uniqueness was done by Rawson et al. . In this study, researchers determined that if five teeth marks can be matched to five teeth, it can be said with confidence that only one person could have caused the bite, and if eight teeth were matched to marks this would be a certainty. However, in this study the probabilities used to make this claim are based on the assumption that the position of each tooth was independent of all the others. This is probably unrealistic because there are a number of ways that the dental profile can be changed. For example, braces apply force to specific teeth, in order to shift the placement of multiple teeth.

One particular case that highlighted the lack of uniqueness in bite marks involved two suspects accused of attacking a man that had sustained a bite mark injury. Two separate forensic dentists, one representing the prosecution and one the defense, were brought in to analyze the mark. They reported conflicting results. One found the mark to come from suspect A and the other said it was from suspect B. This disagreement resulted from the fact that even though the two suspects had dental features making them unique, the bite mark itself was not detailed enough to reflect them. Therefore, the mark could have reasonably come from either of the men. The equivocal outcome demonstrated in the case emphasizes the difficulty in proving uniqueness.

Most of the controversies facing bite mark analysis are due to the lack of empirical supporting evidence. When searching the entire MedLine database from 1960-1999, only 50 papers in English were found that related to bite mark analysis. Of these 50 papers, most of which were published in the 1980’s, only 8% came from well designed experimentation providing empirical data. The lack of research has led to the continued use of a few outdated and limited studies to support the validity of bite mark analysis. This brings into question whether or not there is enough scientific support for bite mark analysis to be employed in court.

There have been several instances when forensic dentists have made claims, accusations, and guarantees supported by bite mark evaluation that have been proven incorrect through other forensic sciences. DNA analysis has shed some light on the limitations of bite mark analysis because often times the DNA from saliva surrounding the area of the bite mark proves to be a more reliable form of identification. In the case of Mississippi vs. Bourne, the DNA of a suspect excluded them from the crime after a dentist claimed the bite marks on the victim matched the defendant’s teeth. In the case of State vs. Krone, the defendant was sentenced to death, which was overturned. Then Krone was later reconvicted and given life in prison. Both convictions were based largely on bite mark evidence, but ten years later DNA evidence surfaced that identified the real killer and Krone was set free.