Forensic Dentistry (Forensic Odontology)

"Forensic dentistry is the study and practice of aspects of dentistry that are relevant to legal problems." (Encyclopaedia Britannica, 2009) ^[1]  Teeth are very resistant to damage by fire, crashes, and explosions, thus, forensic dentistry can be very useful for the following ^{[2, 3, 4]} :

• Identification of human remains from mass disasters (eg, airplane crashes, fnatural disasters, wars, terrorist attacks)
• Identification of multilated, burnt/charred, decomposed, or skeletonized human remains (ie, when usual identification methods, such as fingerprints and visual recognition, are not feasible)
• Analysis of facial injuries in cases of suspected battery
• Analysis and/or identification of bite marks (ie, sex crimes, homicides, other types of crimes)

Historical information

The words "intriguing," "mysterious," and "fascinating" describe the study of ancient remains. Museums abound with archaeologic and anthropologic exhibits that include teeth and jaws (see the following images).

Forensic dentistry (forensic odontology). This artifact is the Ford specimen of retentive prosthesis. The image depicts the anterior teeth of the lower jaw of a male skeleton from an open sarcophagus, Sidon, 5th century BCE.

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Forensic dentistry (forensic odontology). The earliest known human fossil, 1.8 million years ago, was identified as a Homo erectus mandible from Dimanisi in the Republic of Georgia.

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Dental artifacts can shed a wealth of information pertaining to our long dead ancestors and vanished civilizations. Researchers have examined the remains of Homo erectus from Kenya, where growth rates of the dentition were almost twice those of modern man. ^[5] Studies of isolated hunter-gatherer populations show extreme tooth-wear patterns and chipping (see the images below). Interproximal grooving of Hopewellian Indians from Kansas (ca 200-1000 CE) were specific to that group, as there was no evidence of this practice in other skeletal groups of the two regional pre-Colombian populations. ^[6]

Forensic dentistry (forensic odontology). This prehistoric sample differs from the effects of diets of agricultural populations by the relative lack of caries, periodontal disease, wear, and antemortem tooth loss. The arrows point to occlusal chipping in a cast from an adult Batak male, age 28 years. (Turner CG, II, Eder JF. Dental pathology, wear, and diet in a hunting and gathering forest-dwelling group: the Batak people of Palawan Island, the Philippines. In: Harris EF, ed. Dental Anthropology: A Publication of the Dental Anthropology Association. Memphis, Tenn: University of Tennessee; 2006:19(1).)

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Forensic dentistry (forensic odontology). Periodontal disease in a cast from an adult Batak female, age 23 years, is shown. (Turner CG, II, Eder JF. Dental pathology, wear, and diet in a hunting and gathering forest-dwelling group: the Batak people of Palawan Island, the Philippines. In: Harris EF, ed. Dental Anthropology: A Publication of the Dental Anthropology Association. Memphis, Tenn: University of Tennessee; 2006:19(1).)

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Although an Egyptian mandible from 3000-2500 BCE shows evidence of oral surgery, it was not until the 7th century BCE that the Etruscans began to fashion replacements for missing teeth. Dental restorations and tooth replacements were later employed by many geographically diverse, developing civilizations, as can be seen in the following images.

Forensic dentistry (forensic odontology). A piece of iron was placed in the socket of a soldier with a missing molar.

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Forensic dentistry (forensic odontology). Mayans carved shells to fit in empty sockets.

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Forensic dentistry (forensic odontology). Ivory teeth carved to fit in sockets or splinted together were common among the wealthier segments of early civilizations.

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When the Roman Empire expanded to include the Etruscans, their influence in casting gold was acquired. The "lost wax technique" (only relatively recently replaced with optical and laser scans) was a process by which a carved wax pattern of a crown was invested in an iron ring with a gypsum material. After burning out the wax by heating in an oven, molten gold was cast into the ring using centrifugal force. The accuracy of this process emphasized the importance placed on replacing missing or fractured teeth with crowns or fixed bridgework. Note also the Crimes-Table VII, Law X, in the Twelve Tables of Rome:

"When anyone knocks a tooth out of the gum of a freeman, he shall be fined three hundred asses; if he knocks one out of the gum of a slave, he shall be fined one hundred-fifty asses."

Identification through dentition may have begun in 49 BCE with Agrippa, Emperor Nero's mother, who had Lollia Paulina, the mistress of her husband Claudius, killed and her head brought to her for identification by a discolored tooth. Similarly, Nero's mistress had him kill his first wife, who was identified by a canine.

In the Middle Ages, with the exception of a progressive-thinking Spanish Moor in the 10th century, forensic dentistry and dentistry in general abandoned the early techniques in favor of barber-surgeons. Teeth recovered from the Dark Ages have, nonetheless, provided some useful forensic evidence. When modern scientists suspected Yersinia pestis as the cause of the bubonic plague, they were able to confirm their theory by extracting bacterial DNA from some dental pulps.

Over the next 1000 years, little happened in dental forensics. Then, in 1776 at the Battle of Bunker Hill, Paul Revere identified General Joseph Warren by his having previously adjusted the general's dental prosthesis. The next major advances were heralded by the emergence of a novel medical technique at the end of the 19th century-radiology.

See also the following Medscape Drugs and Diseases topics:

• Forensic Anthropology

• Forensic Entomology

• Forensic Scene Investigation

• Forensic Toxicology - Drugs and Chemicals

• Forensic Pathology of Firearm Wounds

• Adjuncts to the Forensic Autopsy

• Postmortem Changes

• Postmortem Radiology and Imaging

• Postmortem Vitreous Analysis

In 1895, the first radiology machines allowed for more sophisticated forensic evaluation, including in dentistry. Internal details of the maxilla and mandible became useful to the dental investigator during examination of the skull. Anatomic landmarks, bone loss, caries, crowns, fixed bridges, and tooth restorations show radiolucencies or radio-opacities in antemortem radiographs, which may later be matched to those on postmortem films (see the following images). However, investigators may be challenged in cases in which there is an inconsistency of radiologic orientation between antemortem and postmortem radiographs. ^[7]

Forensic dentistry (forensic odontology). This is an antemortem radiograph of frontal sinuses.

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Forensic dentistry (forensic odontology). This is a postmortem view of the frontal sinuses seen in the previous image. Dehydration may have accounted for the relative clarity of the film as compared with the antemortem film in the previous image.

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Forensic dentistry (forensic odontology). This radiograph of the maxillary sinus shows another site for analysis when the dentition is missing. (From the private collection of Phil Levine, DDS, Pensacola, Florida.)

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The hardness of enamel and its resistance to temperatures as high as 3632ºC (2000ºF) mean that tooth identification may be useful in air crashes or forest fires, as well as other types of mass or natural disasters. ^{[2, 3, 4]} According to Sakoda et al, postmortem damage from decomposition and fire appear to be more frequently observed in the anterior teeth. ^[8] The development of small and wide-angle radiography scattering, a structural reference for quantitative analysis of heat-affected dental tissues, allows this nondestructive method to determine local dentine/enamel alterations of crystalline shapes, alignment, and hydroxyapatite thickness to provide precise temperature estimation in victim identification. ^[9]

Handheld energy sources have been invaluable in recording dental identification from mass disasters or unidentified remains. Their two-dimensional (2-D) images can be stored to a disk for later dental antemortem comparisons or entered into the database of the National Crime Information Center (NCIC) for missing person identification.

Technology may also influence dental investigators who occasionally collect data using rotational 3-D cone-beam skull imaging. A preliminary study by Tardivo et al used 58 computed tomography (CT) scans to assess 133 root mineralized canines. ^[10] In a time of 20 minutes per tooth, pulp volume/total volume ratios of secondary dentin were measured with 100% accuracy in age and sex determination. ^[10] However, cost, equipment access, and maneuverability may mitigate the practicality of this technology. Currently, 2-D antemortem radiographs, digital or conventional, are prevalent in dental offices and therefore more appropriate when comparing to like postmortem images.

Antemortem radiographs may show the presence of cysts: radicular, dentigerous, lateral periodontal, odontogenic keratocysts, calcifying odontogenic, globulomaxillary, aneurysmal, simple, and static. Although the presence of these lesions on postmortem radiographs may be very useful in some cases, reliance on postmortem films of these anomalies can be problematic because of their rapid decomposition and dehydration. Consequently, the dental investigator tends to rely on evidentiary bony exostoses (tori) (see the following image) and diseases affecting bone morphology and density.

Forensic dentistry (forensic odontology). Mandibular tori (bony mandibular growths) are shown. (From the private collection of Allan Warnick, DDS, Detroit, Michigan.)

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Tori and bony exostoses may be singular or multilobulated and occur in either the maxilla or mandible. Paget disease radiographs reflect a "cotton wool" appearance of skull radiographs along with hypercementosis surrounding the teeth and enlarged maxillary ridges. Hyperparathyroidism with radiolucencies and loss of lamina dura is seen in the mandible.

Craniofacial dysostoses, mandibulofacial dysostoses, and dysostoses from Marfan and Down syndromes are examples of genetic- and chromosome-induced changes resulting in an extremely high vault of the maxilla along with narrow width and extended length of the arches. Malocclusion is common in such cases. The list of benign nonodontogenic tumors includes ossifying fibroma, fibrous dysplasia, osteoblastoma, osteoid osteoma, central giant cell granuloma, giant cell tumor, hemangioma of bone, idiopathic histiocytosis, and coronoid hyperplasia.

In summation, dental osteopathology has been categorized into the following:

• Wear on teeth due to normal or abnormal use

• Bacteria (caries, plaque, abscesses)

• Atrophy of oral cavity contents (periodontal disease, plaque, premature tooth loss, aging)

• Malignant tumors (rare in ancients) and nonmalignant (tori)

• Accidental or purposeful tooth modification

• Congenital and developmental anomalies ^[6]

Methamphetamine and amphetamine use and abuse show pharmacokinetics and pharmacodynamics that may influence clinical tooth dissolution (see the following image). ^{[11, 12]}

Forensic dentistry (forensic odontology). pH drops in saliva, such as occurs with methamphetamine use, coupled with decreased salivary flow from alpha-2 brain receptors, can destroy clinical tooth crowns, leaving dental forensic identification to tooth root morphology and surrounding bone trabeculations.

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Bulimia and tetracycline use during tooth development leave their respective wear/discoloration indicators, and intravenous bisphosphonates have occasionally been implicated in mandibular, maxillary, or otic bone necrosis associated with osteoradionecrosis following head and neck radiation therapy.

See also Tooth Discoloration.

In July 2019, Dr Douglas Price and his colleagues at the University of Wisconsin Madison published their findings in the Journal of Physical Anthropology regarding discoveries of human teeth remains in the Yucatan near Chichen Itza between 600 and 900 AD. ^[13] Using isotope weights of oxygen and strontium in rain and soil, he and his team showed the randomness of human sacrifices by priests. Age, sex, and locale of the victims apparently mattered little in their quest to satisfy the gods.

Historically, age and sex estimates in forensic and archaeologic investigations have involved analysis of cranial and pubic suture closure, numbers/charts reflecting presence of Howship lacunae in cortical bone, and radiographic aging of the femur and auricular surface. The accuracy of these and other procedures remains unclear.

The Demirjian system of age estimation uses eight steps of tooth mineralization, ^[14] but this method has been shown to be subject to varied regional development rates, thereby prompting Ohtani and Yamamoto to pursue amino acid racemization. ^[15] This age indicator begins at the time of death by measuring the rate of change of dentin L isomer to the D form. Although accurate to within 3 years, this method also has limitations, due to a requirement for control teeth, difficulty in separating dentin from other tooth parts, and fabricating a separation column. ^[15] Buchholz demonstrated how to obtain the exact birth year of victims born after 1942 using carbon-14. ^[16] He has used isotopic carbon analysis of developed teeth to determine precise age and obtain clues to the victim’s geographic origin.

Cardoso’s study of sex determination using deciduous crown formation confirms accuracy obstacles discovered by earlier investigators (ie, primary crown dimensions are less sexually dimorphic than permanent tooth dimensions, the degree of dimorphism within and among populations varies). ^[17] Cardoso et al presented a 95% age prediction interval for both sexes. ^[18] Using a developing mandibular canine, for example, measuring 14.20 mm in length and subtracting 1.25 dividing by 1.75, he found the age equaled 7.40 years. However, the 95% prediction interval means that the outlier range could span 5.78 to 9.02 years. He cautioned that these premodern West European studies used only mandibular teeth as samples; and, more importantly, the children of such samples may reflect an era of social and economic factors resulting in delayed dental maturation. His most reliable measurements were of central incisors and first molars; the least reliable were third molars. ^[18]

Lucas et al found that lawyers and social workers frequently inquire about the probability of a certain subject actually being aged 18 years. ^[19] Traditional assessment of third molar development may be of some value in age determination, but in the case of females approaching year 18, there was a 30% chance of misassignment. The authors question the ethics in such matters as affects judicial proceedings. ^[19]  However, more recently, a staging method for third molars on magnetic resonance imaging has been proposed for forensic age estimation, which appears to show comparable reproducibility and performance as radiographs. ^[20]

Complicating age determination are skeletal indicators of stress which include enamel hypoplasia, orbital lesions, and hyperostosis. Additional factors are low socioeconomic status, nutritional deficiencies, childhood anemia, frequent carious lesions, short stature, and parasitic infections (which were present in 65% of the 2000 predominantly young males who died attempting to cross the border into Pima County Arizona from 2001-14). ^[21]

The above studies of sex and age determination may be used as a general guide to victim identification, but a more precise method is required. Assuming antemortem films can be obtained, comparisons to postmortem dental radiographs have long been used by investigators with consistent results.

The following radiographs demonstrate exact points of tooth comparison used by the odontologist:

Forensic dentistry (forensic odontology). These images demonstrate forensic dental comparison of 12 points on 3 teeth. (From the private collection of Allan Warnick, DDS, Detroit, Michigan.)

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Forensic dentistry (forensic odontology). These photographs are postmortem forensic dental comparison of crowns, restorations, bone levels, and endodontics. (From the private collection of Allan Warnick, DDS, Detroit, Michigan.)

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Forensic dentistry (forensic odontology). These photographs demonstrate that after 4 years, the relative points of comparison still exist (arrows). (From the private collection of Allan Warnick, DDS, Detroit, Michigan.)

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Forensic dentistry/odontology: identification in the absence of antemortem records

Mitochondrial DNA samples taken from human molar pulp chambers act as genetic sources and may be useful in identifying victims of natural disasters, explosions, and drowning.

The crewman of the HL Hunley

For example, when the Confederate submarine Hunley was retrieved off the South Carolina coast in 2001 with the human remains of the crew still on board, one of the crew, Seaman Joseph Ridgaway, was identified in 2004 using mitochondrial (mt) DNA by comparing his genome sequence to that of the exhumed remains of Elizabeth Joiner, his sister. ^[22]

Serendipitously, researchers were able to identify the backgrounds of other crewmen, because many soldiers fighting for the Confederacy were foreign (the first regiment to sign up in Charleston was German). "When food is ingested, these isotopes become—and through life remain—deposited in teeth. Thus, by looking at the stable isotope composition in the men's teeth, which they developed when young, the researchers (could) determine if the men were born in the United States or, say, Europe." ^[22]

The Romanovs

The Romanov family was assassinated and dumped down a mineshaft 12 miles north of Yekaterinburg. Later, the bodies of the royal family were retrieved; the bodies had been dismembered, with the faces smashed and sprinkled with sulfuric acid, and reburied. DNA analysis played the key role in identifying the individuals by taking a sample from Prince Phillip, Duke of Edinburgh, a grandson of Victoria (Tsarina Alexandra's oldest sister). ^{[23, 24, 25, 26]} Because mtDNA requires matrilineal transmission, identification was confirmed.

One of these individuals was suspected to be Tsarina Alexandra Fyodorovna of Hesse, owing to the teeth showing amalgam restorations, a luxury at the time. The Czar's remains showed exceptional restorative dentistry as well, but confirmation of his identity was obtained from DNA obtained from his late brother, Grand Duke George Alexandrovich. ^{[23, 24, 25, 26]} Clouding the investigation was the discovery of several unidentified teeth at the burial site. The two missing children Alexei and Marie were located in another grave near the last family burial site.

Adolph Hitler

Another controversial death involved that of Adolph Hitler in 1945. ^[27] Nine months earlier, an attempt on his life had failed, but five skull radiographs were taken at a subsequent physical examination. In late April 1945, as Germany was collapsing, Hitler ordered that his body be doused with gasoline and burned following his and Eva Braun's suicides. The Russians recovered remains (see the images below) at his bunker, took radiographs, and when the US Military Intelligence Service compared the 1944 antemortem films with the postmortem films from the Soviet counterintelligence unit and Russian Federal Security Service, a positive identity was claimed.

Forensic dentistry (forensic odontology). These photographs show the identification of Adolf Hitler from his teeth. Left images: The left upper and lower maxillary bridge as seen from the lingual (inside) view. Right images: The right upper-buccal (front) view of mandibular left bridge, and the right lower-lingual view of the mandibular bridge. Note the severe bone loss around the lower anterior teeth. (From the private collection of Allan Warnick, DDS, Detroit, Michigan.)

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Beginning in May 1945 and lasting over several years, the Russian KGB exhumed and reburied the remains at different locales. The initial Soviet films confirmed that the dentistry on a corpse at the bunker had mandibular anterior bone loss, mandibular bridge #27-29 with #30 cantilevered, and a #9 "window crown." But a 4-9 unit maxillary bridge (depending on the investigator) was not corroborated. Perrier used computer-enhanced images of Hitler's teeth, concluding there was no doubt about the certainty of identification, ^[27] but Dorion compared thousands of close-up photos of the Fuhrer and concluded just the opposite, citing spacing, endodontics, and a porcelain crown mandibular right as evidence. ^[28]  There is agreement, however, about Hitler's severe periodontal bone loss in the mandibular anteriors, which was verified in postmortem radiographs and which may have accounted for irregular tooth spacing.

Skull and blood samples from the Russian state archive were analyzed at the time, showing the remains to be those of a woman 20-40 years old (Eva Braun's DNA was too degraded to show a full range of markers). Finally, as reported by his pilot, Hitler ordered antemortem dental radiographs of all upper-level Nazis be flown to an unknown destination. Only the memories of his dentist and assistant were available to investigators.

Following up on trace mineral analysis of the Hunley project and to determine the identity and relatedness of remains at Fort Niagara, Jennifer Byrnes measured strontium levels in bones and teeth with portable x-ray fluorescence. ^[29] But bone is constantly remodeling, and tooth absorption levels reflect uptake only during formation of deciduous or permanent dentition. Ms Byrnes concluded that identification using mitochondrial (mt) DNA extracted from tooth pulps was more accurate than measuring trace mineral levels. ^[29]

Despite the accuracy of mtDNA identification, mtDNA analysis and sensitivity are usually reserved for trace amounts of sample, as in antiquated or charred remains, ^[30] due to time, expense, and the select few laboratories which test mtDNA. Thus, nuclear DNA typing has become the most widely used technique. The double helix strands contain chromosomes averaging 100 million base pairs of nucleotides, which combine the unwieldy numbers into STRs (short tandem repeats). The DNA can be amplified to develop a profile through the polymerase chain reaction (PCR).

The original (2006) Combined DNA Index System (CODIS) lists the probability identities of 13 standardized core STRs (as of 2017, an additional 7 STR loci are required for uploading DNA profiles to the National DNA Index System [NDIS]), ^[31] but the amelogenin gene is of particular interest to the odontologist, as it is actually the gene for tooth pulp (and sex). Although nuclear DNA testing is very specific, Ashley noted that errors in gathering DNA evidence may develop from soil or blood contamination, infrequent glove changing, storage in plastic bags (bacteria), lack of refrigeration, and the amount of DNA, which affects band intensity, or a second person's DNA. ^[32]

Gum, recent apple bites, dental impression wafers, saliva, licked stamps, toothbrushes, and envelopes may capture low quantities of DNA. Even bacterial infections once thought to contaminate assays can still reveal one-time oral infections. It was assumed that dried out oral hygiene materials were of no evidentiary value, but a study showed that five-bristle toothbrushes all exhibited excellent DNA samples. ^[33] Acrylic in 200-day-old dental prostheses has also provided researchers with sex and tooth-pulp determination by amplifying segments of the amelogenin gene. ^[34]

Researchers at major universities and corporations may soon offer fast, inexpensive single-strand DNA genome sequencing using nanopores. ^[35] The effect of this specific identification technology on odontologic methods remains to be seen.

In 1954, Doyle v Texas was the first modern-day bite-mark conviction that was upheld by the Texas Court of Criminal Appeals; that bite was in cheese and not human skin. ^[36] JJ Layton also pointed to incisal and labial tooth prints in cheese resulting in a London, England, conviction. ^[37]

Overlay techniques reflect hollow-volume perimeters of biting surfaces; transillumination, scanning electron microscopy, reflective ultraviolet photography, and computer-generated and enhanced photography may be useful, but these modalities still depend on the presumption that the individual's tooth size, shape, and position are unique and also that the material bitten accurately conveys the impression. Such technologies may help to verify human bite marks and, acting together, their presence in the courtroom can be convincing. Whether they meet the challenge of certainty presented by a well-prepared defense attorney is another matter. The Daubert Standard of evidence admissibility and expert testimony has five classic parameters of peer review, known error rate, adequate testing, standards controlling use, and general acceptance are regarded as the standard for bite-mark reliability in court, and Bowers has tried to minimize bite-mark error by categorizing types of photographic distortion and position before the investigator resizes or enhances the image. ^[38]

Beyond Daubert, Wood in Canada has noted that the National Institute of Forensic Science suggests an algorithm to replace current standards of terminology, which are based on consensus opinion. ^[39] Even peer-reviewed journals vary in their degree of scientific agreement. Therefore, judicial gate-keeping must account for lack of courtroom scientific background by confining testimony regarding bite marks to the following questions ^[39] :

• Is the patterned injury a bite mark, or is the material presented sufficient enough to make a decision?

• Is the material presented of evidentiary value without further investigation?

• Can the suspected dentition be excluded or not from having made the bite mark?

A 2010 National Academy of Sciences (NAS) report criticized bite-mark evidence ^[40] : "There is no science on the reproducibility of the different methods of analysis that lead to conclusions about the probability of a match...."

The NAS report further stated, “Even when using the American Board of Forensic Odontology (ABFO) guidelines, different experts provide widely differing results and a high percentage of false positive matches of bitemarks using controlled comparison studies.” ^[41] In addition, the report completely neglected to mention that bite-mark analysis as an appropriate methodology in criminal investigations or that when properly applied, bite-mark analysis contributes to successful prosecutions in criminal assault and abuse cases. ^[42] With such limited scientific basis, it is valid to question how bite-mark comparison has reached the level of acceptance that it has. ^[43] Incarceration of innocent people associated with bite-mark evidence has resulted in an added level of scientific scrutiny. ^[44]

The Strategic Litigation Unit of The Innocence Project questions the admissibility of bite-mark evidence but is dedicated to learning and discussing the best ways of challenging such evidence. ^[45] If undisciplined use of bite-mark evidence continues, postconviction defense counsels are advised to critically evaluate any case involving bite-mark evidence in which there exists the potential for innocence and to be cautious to collect all the original documentation. ^[46]

ABFO terms such as “reasonable medical certainty,” “high degree of certainty,” “no doubt in my mind,” “in my opinion,” “the suspect is the biter,” “beyond a reasonable doubt,” and “99% certainty” may bring suspicion on the guidelines themselves.

Publicity surrounding the 1970s Tallahassee Chi Omega murders featured bite-mark evidence as the deciding factor in the conviction of Theodore Bundy (see the following images).

Forensic dentistry (forensic odontology). This is a wax bite exemplar of Ted Bundy's lower front teeth.

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Forensic dentistry (forensic odontology). A frontal view of Ted Bundy's teeth is shown.

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Forensic dentistry (forensic odontology). This image demonstrates the edges of Ted Bundy's teeth #22 through #27 made as a compound overlay via digital compositing methods.

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Forensic dentistry (forensic odontology). A digital superimposition of the original hand-drawn overlay onto Ted Bundy's bite mark is shown.

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Forensic dentistry (forensic odontology). This photograph depicts the buttock of Lisa Levy after having been bitten in different directions. Only the unique arrangement of Bundy's lower teeth (as shown in the wax imprint image) made it possible to place the overlay as shown.

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Note the unique tooth marks (see the images above) that were left from Bundy's actual double bite marks on Lisa Levy's buttocks. Not shown was the result of an attempt to corroborate these findings when Dr Richard Souviron, forensic odontologist, asked the guard to give Bundy an apple. After his first bite, it was taken for an impression. The attempt was described as a "partial success," because the apple had distorted between the time of the bite and taking the impression.

The Bundy cases' notoriety promoted the “revelation” that tooth and fingerprints were equally unique and therefore reliable. Although untrue, it has been easier for attorneys to argue and jurors to visualize such cases in court. Computerized overlays and build-ups of teeth can be quite dramatic in court as the dental model's incisal edges are slowly lowered to "match" the marks on a photo. Whether these marks were tooth borne, insect, chemical, pathologic, or trauma is the question.

Controversies

Over a period of years, controversy over bite mark evidence has ensued. ^{[47, 48]}  In a 2008 article, Saks and Faigman citied eight cases in which there was disagreement among forensic odontologists as to whether the bite marks were from the accused or even human in origin. ^[47] The viscoelastic nature of the victim's epidermis may have altered a reproducible biting force. ^[49] In addition, the associated bruising, edema, vessel rupture, and inflammation may have produced indistinct results. ^[47]

Souviron has pointed out that refrigeration time, temperature, humidity, light, and gravity are further variables that affect bite marks. ^[50] Enhancement of the traumatic lesion due to victim dehydration, gravity's tendency to move blood from normal tissue but not from an injury, the questionable theory of collecting bite-mark evidence as soon as possible, along with inconsistencies of photographs and radiographs are factors which further cloud the science. Kittleson and Kieser concluded that "more than 150 years of developments in bite mark evidence still leaves us without some sort of consensual basis to decide whether or not bite mark evidence should be admitted." ^[51] Plourd allows that although there is evidence that a person's teeth can be unique, what little scientific evidence that does exist supports the conclusion that crime-related bite marks are grossly distorted, inaccurate, and therefore unreliable as a method of identification. ^[40]

Moreover, psychological bias may exist as the investigator interprets odontologic evidence with the desire to conform to the beliefs and perceptions of others. Even terms such as “victim” or “perpetrator” may lead to confirmation bias by the investigator. Motivational or cognitive effects such as the following may challenge the objectivity of the odontologist’s testimony ^[52] :

• Hawthorne effect: Tendency to perform when one is in the spotlight

• Contrast: Tendency to rationalize weak evidence associations over time

• Overconfidence: Jury’s tendency to be influenced by expert’s demeanor

The following are examples and problems associated with odontology's attempt to bring credence to bite-mark evidence: Photos of bite marks on a body, impressions, and casts using Adobe Photoshop computerized reproductions; spectroscopic, infrared reproductions; transillumination; and photography with two calibrated, perpendicular reference rulers are recognized instruments used in gathering forensic data. However, although incisal painting of these reproductions, along with polyline measurements of mesial distal tooth widths or rotation and interarch canine distances appear reasonable scientific procedures, they may have been distorted by alginate impression shrinkage or postmortem decomposition. ^{[53, 54]}

Even if photographed immediately, three-dimensional (3-D) bite marks on a 2-D photograph will be associated with changes in color and spatial relations; skin associated with curved surfaces is an unreliable impression medium and distorts more easily than biting flat surfaces. ^[55] A struggling victim and jaw thrust of the suspect during the attack are additional variables that obscure evidence.

Some investigators feel that the value in bite-mark evidence lies in the likelihood of identifying those not involved through missing dentition rather than a positive identification, such as in the case of a wrongfully incarcerated Milwaukee man who was convicted on bite-mark evidence but which DNA evidence refuted and who served 24 years before being exonerated. ^[56] This and another similar case have caused some odontologists to voluntarily retract previous testimony.

The ABFO has considered a paradigm review regarding bite-mark evidence, wherein the terms "degree of certainty, probable/possible" have clouded the "beyond a reasonable doubt" legal presentation. The term "match" with regard to bite-mark evidence may eventually be replaced with a suspect being "one who cannot be excluded as a person of interest." Therefore, bite-mark evidence by itself appears to have limited use in positive identification, but it may serve along with a constellation of factors to supplement a position presented in court. The ABFO released its most recently revised standards and guidelines for evaluating bite marks in 2018. ^[57]

A study of evidentiary court challenges to fingerprints, handwriting, firearms, tool marks, ballistics, and forensic documents found that the largest proportion of restrictions because of reliability was that of forensic odontology. “Unsatisfactory, careless, and troubling” were used to describe court criticisms of all evidence admissibility, which may have prompted Vermont Senator Leahy to propose the “Criminal Justice and Forensic Science Reform Act of 2011.” That initiative was supported by the National Association of Criminal Defense Lawyers at its June 2011 meeting, with an agenda including a 3-day seminar on forensic odontology. ^[58] An interview with the past president of the American Academy of Forensic Sciences (AAFS) revealed some congressional hesitation in support of Senator Leahy’s proposal.

Even more comprehensive regulation is being considered as the American National Standards Institute (ANSI) has approved American Dental Association (ADA) specification no. 1058 for forensic dental data set as a national US standard. Their goal is to standardize methods and nomenclature ("Informatics") in dental data collection for entry in an electronic format. ^[59]

A review of the 2012 AAFS Annual Scientific Meeting Proceedings shows a variety of studies regarding validity/reliability of bite mark evidence. By itself, bite mark evidence is viewed by some as poor-to-nonexistent science. ^{[48, 60]}  Others attempt to gain forensic credibility by classifying the degree of bite mark quality. ^[61] Convictions have been obtained based solely on models along with 20-year-old bite mark photographs, perhaps subjected to light (“white balance”) color and lens aberrations. ^[62] A study of bite mark characteristics using live subjects showed all volunteers but one having no indentations after 2 hours of healing. The “biting” force required to produce a 24-hour indentation ranged from 60 to 235 lb. ^[63]

Compounding the above is the use of artificial intelligence (AI) in forensic photography and questions raised by their authenticity when presented in court. Thus, bite mark evidence appears to falling further out of favor. ^{[48, 64]}

Charting teeth for identification is usually subject to the available forms in the medical examiner's office and may include the Universal Numbering, Palmer Notation, or FDI (Federation Dentaire Internationale) World Dental Federation numbering methods. Of these three systems, the Universal seems to be most widely accepted (see the images below). In this case, the teeth, starting with the maxillary right third molar, are designated #1-16, ending with the maxillary left third molar; and #17-32 from the mandibular left third molar, ending with #32, the mandibular right third molar.

Forensic dentistry (forensic odontology). An example of an antemortem dental record is shown.

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Forensic dentistry (forensic odontology). An example of a postmortem dental record is shown.

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A continuing challenge in this area is to standardize all record keeping. The forms used at various schools, reading of radiographs, and conducting clinical dental examinations may hinder consistent record keeping. In 1984, the American Board of Forensic Odontology (ABFO) guidelines sought to clear up this confusion by proclaiming the Universal Numbering System as the recommended method for dental charting. Unfortunately, the "button out" versus "button in" orientation may reflect military versus school protocols for reading conventional films and recording clinical findings. Digital radiographs, whether hand held or stationary, should help speed the charting process.

The forms used by the Armed Forces Institute of Pathology (AFIP) are compatible for entry in the Federal Bureau of Investigation (FBI)/National Crime Information Center (NCIC). Antemortem radiographs may be placed next to the postmortem films in the courtroom such that a complete set of films must be taken.

The primary challenge in evidence gathering for forensic dentistry consists of standardizing investigator collection methods. As previously noted, errors in collection/interpretation can be found in everything from bite marks to radiographs to DNA (see the Bite-Mark Evidence section). High-profile court cases, for example, bring awareness to such legal vulnerability.

Avoiding the following terms may help reduce legal confusion in the courtroom:

• The statement “based on my training and experience” made at the beginning of expert testimony may lead to the opposing attorney’s assumption that the rest of the sentence is speculation in justifying a conclusion. ^[65]

• “Theory" and "possibility” are expansive terms reflecting a degree of certainty not usually recognized in environmental forensic science but found in religion and philosophy.

A legislastive bill introduced by Senator Patrick Leahy and co-sponsors in January 2011 was intended to establish an Office of Forensic Science and a Forensic Science Board as a means to strengthen and promote confidence in the criminal justice system. Their initial goal was to ensure consistency and scientific validity in forensic testing until they encountered National Academy of Sciences (NAS) criticism of each forensic discipline area’s reliance on Scientific Working Group (SWG) guidelines administered by NIST (National Institute of Standards and Technology). NAS maintained that SWG guidelines and best practices were not independent enough in separating forensic science from law enforcement.

Thus, in February 2014, and in accord with the Department of Justice (DOJ), the funded nonregulatory NIST’s task of ensuring forensic consistency and scientific validity was turned over to the Organization of Scientific Area Committees (OSAC). Its organizational chart consists of five Scientific Area Committees (SAC) reporting to a forensic science standards board (FSSO), plus legal resource, and 25 forensic subcommittees as well. ^[66] Hundreds of members named to the FSSO coordinate development of forensic community standards and guidelines. Specific operational needs such as for DNA or digital evidence may cause the DOJ to retain a few SWG guidelines, but the majority of SWG guidelines and best practices will be abandoned in favor of scrutiny by the Human Factors Committee (HFC) to mitigate cognitive and confirmation bias, public vetted Quality Infrastructure Committee (QIC), and Legal Resource Committees (LRCs) for professional code of ethics adherence. ^[67]

Persson at the University of Linkoping, Sweden, ^[68] and Thali et al at the University of Berne, Switzerland, ^[69] have tried to mitigate errors in forensic evidence gathering by developing a virtual imaging system whose multislice computed tomography (MSCT) images can be opened and closed without distorting evidence. Their 3-dimensional (3-D), color-enhanced, 1+ mm–resolution, rotational images are captured by a "flash" scan, which can record up to 24,000 body slices in seconds.

As pointed out at the end of the Radiology and Forensic Odontology section, the expense and logistical problems associated with 3-D CT scans make 2-D images more efficient in dental identification. Still, the value to dental identification is the 3-D, rotational, reproducible images of the oral cavity. Antemortem radiographs, whether digital or conventional, can easily be compared to postmortem images of crowns, bridges, amalgam, or composite restorations, prostheses, tooth and root angulations, trabecular bone patterns, and anatomic landmarks. (See the following images.)

Forensic dentistry (forensic odontology). These images demonstrate forensic dental comparison of 12 points on 3 teeth. (From the private collection of Allan Warnick, DDS, Detroit, Michigan.)

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Forensic dentistry (forensic odontology). These photographs are postmortem forensic dental comparison of crowns, restorations, bone levels, and endodontics. (From the private collection of Allan Warnick, DDS, Detroit, Michigan.)

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Forensic dentistry (forensic odontology). These photographs demonstrate that after 4 years, the relative points of comparison still exist (arrows). (From the private collection of Allan Warnick, DDS, Detroit, Michigan.)

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The International Organization of Police Chiefs (IAPC) Committee to Identify the Missing has proposed registering all dental implants. An identification number plus the manufacturer, type, and year could reduce the number of consulting dentists in forensic identifications from 165,000 to the approximately 200 who use that manufacturer’s appliance. ^[70]

Early oral CT scan interferences (streaking) were due to dental amalgam or crown prostheses and have been replaced with color-coded density assignments to both metals and composite restorations. Although these technologic advances are of inestimable time value in postmortem dental identification following disasters such as the 2004 tsunami or 2010 Haitian earthquake, ^[69] they are even more important as a reproducible evidence source.

Forensic odontologists should be aware of the changing courtroom atmosphere and act accordingly before presenting evidence. The "CSI" effect from television shows has brought unrealistic expectations from non–science-oriented juries seeking absolute proof of forensic science. ^[71]   Knight, Durnal, and Robbers in separate studies have shown awareness and possible misguided expectations of certainty or "matches" from DNA or fingerprints. ^[71] Even negative witnesses have been brought in to explain the problems associated with seemingly conclusive evidence. In addition, criminals are becoming aware of using bleach to kill DNA, taping envelopes, and wearing gloves as methods of subverting crime scene investigation.

The dental investigator has been accustomed to showing the antemortem and postmortem comparisons of teeth, restorations, and maybe bone anomalies, as conclusive evidence in forensic identification. Perhaps the now skeptical juror will need additional science. Or maybe the criminal, anticipating dentistry's role in identification, will attempt to obviate that possibility with preemptive destruction of dental evidence.

Examination of written dental records is essential to positive identification, especially regarding confirmation of socket augmentation. Radio-opaque materials are now used to maintain the osteointegrity of maxillary/mandibular dental sockets following extractions. Instead of the usual radiolucency associated with tooth removal, these areas may appear as retained root tips—thereby confusing odontologic confirmation. Therefore, the dental records must be checked routinely to assure accurate identification.

It is important to recognize the value of dental forensic identification from the early ancients to the present. From natural disasters to atrocities to mysterious disappearances, dental remains have been a universally used tool to determine identification, lifestyles, culture, and societies. Forensic dentistry remains an efficient means of recognizing the identity of the deceased.

At the 2014 66th Annual Scientific Meeting of The American Academy of Forensic Sciences (AAFS) held in Seattle Washington, National Academy of Sciences (NAS) scientific areas of “analytical” or hard evidence (DNA, chemical, materials, fire, explosives) were featured sections, as well as odontology, which leaned more toward “pattern/experience” or soft evidence (fingerprints, bite marks, blood stain patterns.). ^[72] The American Board of Forensic Odontology (ABFO) has tried mitigating NAS validity concerns regarding the odontology section by updating standards, guidelines, human bite-mark classification, certification, and, especially corroboration/challenge of several expert opinions regarding reproducibility of bite-mark evidence. ^{[57, 73, 74]}

Additionally, current presentations attempt to enhance the validity of bite marks by using technology, as in the following examples ^{[75, 76, 77, 78, 79]} :

• Correction of crime scene camera angles

• Use of GNU Image Manipulation Program (GIMP) to fabricate bite-mark overlays

• Three-dimensional bite-mark analysis

• Recognition of positional distortions in hollow-volume overlays

• Use of simulated bites on live volunteers, with and without high-speed videography

• Cone-beam computed tomography (CT) imaging

• Password-protected technology to transfer ante mortem records via images attached to texts, emails, smartphones, computer tablets, or laptop computers

Computer vision appears to be a feasible and relatively quick method for automatic antemortem and postmortem comparison of panoramic radiographs for identification of individuals. ^[80]

Whether such attempts as those listed above can blunt the NAS’s criticism that bite marks are of limited evidentiary value remain a question. However, to ignore tooth-mark evidence and set a perpetrator free is in no one’s interest.

Skin as the recording medium is viscoelastic in nature and, coupled with a struggle, makes reproducibility impossible. Wright, in his presentation, states that, “the uniqueness of the human dentition as it relates to human bitemarks in living skin has not been proven in large open-population studies.” ^[79]  (In an earlier presentation, he had referred to the subjective term, “high-quality” bite-mark evidence without defining the term or differentiating high quality from medium-high quality or medium quality.)

Page, in a study of 15 odontologists with varying opinions of the six images they were shown, concluded that the assessment criteria were so disparate that the NAS’s position of odontology bite-mark evidence in forensics was “fair at best.” ^[81] Aleksandravicius, when comparing mechanical dental clamping simulations to actual bites during violence, concluded that, “it is difficult and may be impossible, to fully reconcile the reproducible science.” ^[82]

Therefore, as suggested by other presenters, ABFO may do well to accept its role as support for and reliance on other AAFS disciplines.

A study by Roberts et al compared the effectiveness of swabbing and flossing as a means of recovering spermatozoa from the oral cavity following sexual assault. ^[83] Swabbing was more effective than flossing, so long as the collection time of postcoital interval (PCI) was 1.5-12 hours. At 24 hours, the two methods were equally effective in terms of the percentage of subjects from whom spermatozoa was recovered, as well as semen concentration. If the PCI is longer than 24 hours, floss may present more information than swabbing. However, degradation of spermatozoa is subject to various factors that are difficult to control, including rinsing, toothbrushing habits, eating, and drinking. Other variables affecting the study included expectoration, swallowing the semen, the victim’s postassault hygiene activities, delays, and avoidance of reporting. Although the two methods combine to increase the percentage of subjects with recoverable spermatozoa, the report was not controlled. The wide activity disparity between the subjects also compromised the study’s results. ^[83]

Speakers from recognized reproducible-evidence disciplines might provide the odontology section with a reliable appreciation for DNA collection, toxicology analysis, entomology, veterinary medicine, and chemicals, among others. Combining objective or hard evidence with bite marks may be useful in mitigating criticism of bite marks in this team approach. ^{[84, 85]}

Although bite-mark evidence does have a place in the court system, it should be used with a constellation of factors in which evidence has been gathered with the utmost care to prevent misidentification. Thus, in the interest of objectivity, as well as in anticipation of court challenges, precautions in data collection must be rigidly observed. Therefore, the definition of forensic dentistry presented initially in this article should be amended from "the study and practice of aspects of dentistry that are relevant to legal problems" to include the more thorough phrasing of the ABFO, "the careful and proper handling of dental evidence for legal matters."

The following resources ares recommended for more detailed information regarding forensic dentistry:

• Bowers CM. Forensic Dental Evidence: An Investigator's Handbook. 2nd ed. San Diego, Calif: Academic Press; 2010.

• Dorion RBJ, ed. Bitemark Evidence: A Color Atlas and Text. 2nd ed. Boca Raton, Fla: CRC Press; 2011.

• Fixott RH, ed. The Dental Clinics of North America (Forensic Odontology). Philadelphia, Pa: WB Saunders Company; 2001:45(2).

• Thali MJ, Dirnhofer R, Vock P, eds. The Virtopsy Approach: 3D Optical and Radiological Scanning and Reconstruction in Forensic Medicine. Boca Raton, Fla: CRC Press; 2009.

• Turner CG, II, Eder JF. Dental pathology, wear, and diet in a hunting and gathering forest-dwelling group: the Batak people of Palawan Island, the Philippines. In: Harris EF, ed. Dental Anthropology: A Publication of the Dental Anthropology Association. Memphis, Tenn: University of Tennessee; 2006:19(1). Available at: http://journal.dentalanthropology.org/index.php/jda/article/view/115/108. Accessed June 19, 2019.