21: Forensic Odontology

Forensic Odontology

The word forensic, states Clark, is derived from the Latin forensis, which means ‘before the forum’. According to Jones, in ancient Rome the forum was a public square where trials and debates took place and consequently served as a court of law. Odontology refers to the study of teeth, and in effect denotes dentistry. Forensic odontology, therefore, has been defined by the Fédération Dentaire Internationale (FDI) as ‘that branch of dentistry which, in the interest of justice, deals with the proper handling and examination of dental evidence, and with the proper evaluation and presentation of dental findings’. It primarily deals with identification, based on recognition of unique features present in an individual’s dental structures. Forensic dentistry plays a major role in identification in man-made or natural disasters—events which result in multiple fatalities that may not be identifiable through conventional methods such as visual recognition or even fingerprints. According to Harvey, the earliest known example of identification by dental means dates backs to 66 A.D. There have been numerous instances over the last two millennia in which dental remains played a major role in identification of deceased individuals. Elaborate dental records including radiographs and spare crowns identified the body of Adolph Hitler, probably the most publicized case of dental identification. In addition to postmortem identification, dental evidence can be crucial in crime investigation as in, for example, bite mark investigation and determination of whether an individual is a juvenile or an adult.

In the last half-century, forensic odontology has made great strides and has evolved as a separate specialty. It relies on sound knowledge of the teeth and jaws possessed by dentists and incorporate dental anatomy, histology, radiography, pathology, and dental materials.

Forensic odontologists delve into:

Personal Identification

Identification is the establishment of a person’s individuality. Proper identification of the dead is required both for legal and humanitarian reasons. It may help in the settlement of property and insurance, facilitate remarriage of a surviving spouse, and allow the cremation or burial of the body, according to appropriate religious and cultural customs.

Traditional methods of identification have included visually recognizing the body, and personal property such as clothing, jewelry and the like. These methods, however, are not very reliable in establishing the identity. Visually identifying a body that is burned or decomposed is not only unreliable but also can be a very traumatic experience for relatives and friends. The more appropriate approach is for forensic experts to analyze physical features present in the body, thus enabling a scientific means to identification.

In general, physical features may be inherited or acquired. While inherited features include characteristics such as hair color, height, and dental features such as Carabelli’s trait, among others, acquired features may be surgical scars, previous fractures, or dental restorations. Physical features however are prone to change over time. Epidermal ridges on the fingers (that produce fingerprints) are exceptions but, like other soft tissue, undergo postmortem change.

Dental hard tissues gain importance in identification based on the condition of the human remains. Teeth are one of the strongest structures in the body, and are usually resistant to postmortem decomposition. Moreover, most materials used by the dentist for restoring and replacing teeth are also resistant to postmortem changes. Therefore, the use of dental evidence is the method of choice in establishing identity of badly burned, traumatized, decomposed, and skeletonized remains.

Basis for Dental Identification

The basis for dental identification is the theory that human dentition is never the same in any two individuals. In a much cited work, Keiser-Nielsen has assessed the ‘uniqueness’ of teeth mathematically. The morphology and arrangement of teeth vary from person-to-person. Although teeth are relatively resistant to environmental insults after death, during life they are susceptible to physiologic and pathologic changes. As a result, teeth may have been restored. Those teeth that are beyond restoration may have been extracted and, thus, missing from the mouth. The number of combinations 16 missing teeth can produce is approximately 60 crore (600 million). Sixteen filled teeth produce a similar combination. Four missing and four filled teeth in a mouth combined can produce more than 70 crore combinations (700 million combinations). All teeth have five surfaces. If, instead of considering the whole tooth, the surfaces were taken individually, the variations produced would be astronomic. In fact, Fellingham and coworkers have calculated that there are 1.8 × 1019 possible combinations of 32 teeth being intact, decayed, missing or restored. Hence, dental identity has been defined by Acharya and Taylor as “the total of all characteristics of the teeth and their associated structures which, while not individually unique, when considered together provide a unique totality”.

Dental Identification Procedures

There are essentially two forms of dental identification: the first known as comparative identification, attempts conclusive identification by comparing the dead individual’s teeth with dental records of the presumed individual. This is possible when some clue (through circumstantial evidence) exists about the possible identity of the deceased. The second, reconstructive identification or dental profiling, attempts to elicit the population affinity or race, sex, age, and occupation of the dead individual. This is undertaken when virtually no clue exists about the identity of the decedent.

Oral Autopsy

Autopsy, also known as necropsy or postmortem examination, involves examining the deceased usually with dissection to expose the organs to determine the cause of death. Autopsy has a systematic protocol starting with critical examination of the external features of the body such as gender, ethnicity, build, wounds, scars, tattoos, and body piercing. Photographs, radiographs, fingerprints, fingernail scrapings, hair sample may be obtained, as necessary.

Oral examination is ideally an essential part of the postmortem examination (Fig. 21-1). The forensic dentist who conducts oral autopsy should have adequate knowledge about common postmortem findings such as rigor mortis, livor mortis, decomposition and postmortem artefacts. Rigor mortis may render the jaws rigid and the use of mouth-gags, trismus screws, or intraoral myotomy is essential for jaw separation. In cases of incinerated remains, additional challenges are faced—since teeth may be brittle following exposure to prolonged heat, they need to be reinforced with cyanoacrylate glue prior to examination. According to Griffiths and Bellamy, access for radiography in incinerated bodies can be obtained by removing the tongue and contents of the floor of the mouth in a ‘tunneling’ fashion from beneath the chin. Although oral examination may be challenging at times owing to certain postmortem alterations, the status of each tooth (whether visibly intact, carious/diseased, restored or missing) should be carefully noted. A thorough examination of soft tissue injuries, para-oral hard tissue fractures, and presence of foreign bodies is undertaken and samples of hard and soft tissues may be obtained for further investigations. All information pertaining to the body must be entered into the modified Interpol postmortem dental odontogram (Fig. 21-2).

Comparing Post- and Antemortem Dental Data

Following postmortem examination and transcription of antemortem data, the two odontograms are compared. Features evaluated include tooth morphology and associated bony structures, pathology, and dental restorations (Fig. 21-4). An individual with multiple dental treatment and unusual features has a better likelihood of being identified than someone with no extraordinary dental characteristics. This, however, does not imply that identification relies on extensive dental treatment—comparison should take into account quality rather than quantity. Acharya and Taylor have concluded that a single point of concordance between post- and antemortem data may be sufficient to establish identity, considering, of course, the uniqueness of such a feature and circumstances of the case.

Writing a Report and Drawing Conclusions

One needs to remember that any attempt at establishing identity is addressed to the law enforcers or legal authorities. Therefore, a detailed report and factual conclusion based on the comparison must be clearly stated. The quality and quantity of information required for establishing dental identity has not been fully determined. In fingerprinting, differences in the ante- and postmortem data rule out identification. This concept does not apply to dental identification so long as the inconsistencies are explainable. For example, the postmortem data may reveal a ‘filling’ on the right upper first molar but the dental records show the same tooth as ‘intact.’ This difference, however, may be explained on the basis that the restoration was made on a date after the available dental records by a different dentist, but for which no records are available. On the other hand, if the postmortem data shows an ‘intact’ right upper first molar, whereas the same tooth is ‘filled’ in the dental records, this would probably indicate a mismatch. It is essential to explain these considerations in the report for the purpose of clarity. Having compared and weighed the two sets of data, one should ask the questions: “Are the similarities significant?”, “Can the differences be explained?”. Based on this, a range of conclusions can be derived, which have been modified below from McKenna, Silverstein, and Acharya and Taylor.

Use of Ameloglyphics in Personal Identification

Tooth prints are the pattern formed by the enamel rod ends at the crown surface of the tooth. Manjunath and coworkers recorded the enamel rod end pattern using acetate peel technique (a technique used to study the texture and surface details of rocks and fossils). Based on their recent study that examined 60 subjects and 120 teeth, they have categorized tooth prints into eight different patterns and demonstrated that no two teeth have similar pattern and coined the term ameloglyphics (Fig. 21-5). However they have raised doubts regarding its forensic value since enamel undergoes regressive changes and the course taken by the enamel rods vary at different levels of the enamel.

Identification in Disasters

Disasters refer to natural calamities such as earthquakes, floods and tsunami and accidental or man-made events—such as airplane crashes or terrorist attacks—that result in multiple human fatalities. Such incidents require identification of the postmortem remains due to severe mutilation. The process of dental identification is essentially the same as described previously except, the magnitude of the event is far greater. It involves examining and comparing hundreds, sometimes thousands, of post- and antemortem data. Human remains in such events may be highly fragmented and, hence, only part of the body may be recovered. The bodies may be incinerated or commingled (i.e. parts of two bodies are mixed with each other). Vale and Noguchi state that disasters may involve exorbitant monetary lawsuits, making it an added reason for prompt and accurate identification; also, there are political and jurisdictional issues that may need to be addressed. For example, Keiser-Nielsen states that in some countries, an airplane is considered ‘national territory’—in case an airplane registered in one country crashes in another, the victims may be considered as having died in the former country’s territory. Hence, experts from that country may be required to assist in identification. Airplane crashes usually involve victims from diverse countries and acquiring relevant dental records from distant regions can be daunting.

Dental Section

Forensic dentists are usually part of a team of identification specialists that include anthropologists and fingerprint experts, to name a few. Each team has its own section where postmortem identification is carried out. According to Clark, almost 50% of identifications in disasters are from dental evidence. Therefore, most disaster victim identifications have an odontology section. Representation on this section should be as broad as possible and inclusion of different specialists and dental auxiliaries can be useful. Each team member should be familiar with procedures to be followed in a disaster situation. Information about team activation, the tasks to be performed, and standardized charting methods should be known in advance. Tasks may range from taking radiographs to performing clerical duties. The Interpol’s disaster victim identification guide as well as Vale and Noguchi suggest the division of the odontology section into three sub sections— postmortem unit, antemortem unit and the comparison and identification unit.

Postmortem Unit

According to Vale and Noguchi, it is useful if members of the forensic dental team are part of the search and recovery team at the site of disaster since dentists are more likely to recognize fragmented and burned teeth. They suggest that at the disaster site a sketch should be made of the scene. The location at which a body is recovered is noted and preliminary examination of the mouth is made on-site to evaluate the oral condition. The definitive dental examination however, is best performed at the temporary mortuary set-up for postmortem examination.

Clark states that dental examination is usually done after most other procedures such as photography, fingerprinting and medical autopsy. This allows sufficient time to organize the postmortem unit. Portable dental radiography apparatus should be installed at a convenient area within the temporary mortuary, taking precaution against the risk of radiation hazard. The postmortem unit is responsible for processing the radiographs and may also need to arrange for photography of teeth. Teeth and jaw specimens may be removed from a body for convenience of examination. These must be appropriately labeled to prevent a ‘mix-up’.

Antemortem Unit

Morlang considers the task of the antemortem unit as the most difficult. The members need to collect as much information as possible in the shortest period of time. This begins with locating the dental records of the victims, which requires an extensive network of communication with the police, relatives of the victim and the victim’s dentists. It is essential to re-check the verbal information obtained with the victim’s dentist. This dentist is requested to provide the written records, radiographs and study models to the antemortem unit. The Interpol’s guide has stressed that personnel in this unit should be capable of reading and interpreting all dental records obtained. The quality, quantity, and variety of dental records present a major obstacle to this unit (see Box). Since transcribing and copying could reduce the quality of antemortem information, it is recommended that original records be obtained. All information gathered must be transferred onto the Interpol antemortem odontogram (Fig. 21-3).

Comparison and Identification Unit

This subsection handles comparison and confirmation of identity. In addition, the unit has the potential to exclude identity. Vale and Noguchi recommend commencing comparison and identification once postmortem information from all the victims is available. Antemortem information from all victims may or may not have been procured. The comparison may be done manually or by computer aid. When manual, Clark suggests that the data can be sorted by sex, age, presence or absence of restorations, etc. This eases comparison to some extent when hundreds of data exist. According to Vale and Noguchi, the antemortem data is taken individually and compared to the postmortem data that is spread out, for example, on a table. The Interpol’s guide states that fragmentary remains will need to be cross-checked with individual bodies. When there is a match, one must ensure that all sets of documents relating to dental features are attached to the relevant sets of documents for the rest of the body.

A number of computer software programes such as IDENTIFY, ODONTID, CAPMI and IDIS have been developed over the last two and half decades to simplify comparison. In addition, the Interpol has recently facilitated access to and free use of a software program called ‘Plass Data DVI System International’. Using Interpol’s post- and antetmorten forms, the software allows the investigators to enter both post- and antemortem data, which is then analyzed and compared to enhance the matching process and assist in identification. However, these programs merely sort the data, bringing down the number to a few likely post- and antemortem data. Clark stresses that the final identification should always be done by the dentist manually, which is based on personal evaluation of evidence. In problematic cases, it is useful to consult with other methods of identification, such as anthropologists and fingerprint experts. This is reciprocal in nature and adds to the ultimate success of identification in disasters. In fact, the Interpol’s guide states that the success of disaster identification depends on the active participation and cooperation of different identification teams.

Identification from Dental Dna

The conventional method of dental identification described thus far requires one basic element that may not always be readily available—dental records. Lack of adequate or complete absence of antemortem records is not uncommon and is known to undermine the identification process; this, however, does not necessarily preclude identification. Since teeth can resist extreme conditions, Pretty and Sweet state that teeth are an excellent source of DNA. One may doubt the ability of teeth to yield sufficient quantities of DNA for analysis, particularly under circumstances when the postmortem interval ranges from a few months to years. However, Pötsh and coworkers successfully extracted DNA from the pulp of teeth recovered from decomposed and burned bodies, as well as victims of air crashes. Moreover, a routinely applied technique in forensic investigations—the polymerase chain reaction (PCR)—allows amplification of even highly degraded DNA. This facilitates comparison with a known biological antemortem sample of the decedent, such as hair from a comb, epithelial cells from a toothbrush or biopsy specimen. A major advantage of DNA analysis over comparative dental identification is that if a decedent’s antemortem sample is unavailable, DNA pattern may be compared to that of parent(s) or sibling(s), thus facilitating confirmative identification.

Types of DNA

Pretty and Sweet have pointed out the use of two types of DNA. The first is called genomic or nuclear DNA, which is located in the nucleus of cells and commonly used in forensic cases. The second, known as mitochondrial DNA (mtDNA), is present in the mitochondria of cells. While most cells have a single nucleus, Bender and associates point out that the major advantage of mtDNA is that each cell has a high copy number of mtDNA. For example, epithelial cells contain 5,000 mtDNA molecules and, hence, mtDNA can substitute in cases where nuclear DNA is unavailable. Also, mtDNA is exclusively inherited from the mother, and there is no contribution whatsoever of the father. Thus, an identical mtDNA pattern is observed among siblings, their mother and many maternal relatives. Moreover, due to their exclusive maternal inheritance, they can be used to establish identity in cases where there is a gap of several generations.

Extraction of Dental DNA

Owing to its neurovascular nature, the tooth pulp is considered to be the best source of dental DNA. Ajayprakash and coworkers isolated DNA from dental pulp and accurately determined personal identity using HLA-DQ amplification. Sweet and Hildebrand have advocated a method known as cryogenic grinding for extracting DNA. This involves cooling the whole tooth to extremely low temperatures using liquid nitrogen and then mechanically grinding it to fine powder. Using standard protocols, they were able to obtain sufficient amounts of DNA from intact, carious as well as root-filled teeth. Extraction of DNA from the latter implies that pulp tissue is not necessarily the only source of dental DNA—hard tissues such as dentin and cementum may be equally viable. This is of particular significance in skeletal remains. In fact, applying this method on a 3½ year-old skeletal specimen, Sweet and associates were able to accurately identify the remains.

The major drawback of cryogenic grinding is that the tooth needs to be completely crushed. This is a drawback since, in forensic investigation, methods that circumvent the need for tooth destruction are preferred as the tooth sample may need to be presented later as part of the evidence in courts.Therefore, Trivedi and coworkers have suggested a less destructive method for DNA isolation. Their method involves accessing the root canals through an opening similar to that made during root canal treatment, scraping the pulp area with a notched medical needle, and subsequent flushing of the tissue debris. This, the authors claim, ‘retains the morphology and physiology of the tooth’. Most methods yield variable quantities of DNA from the same type of tooth. Hence, for optimal results, one may need to utilize multiple teeth.

Palatal Rugae in Identification

In the preceding columns, identifying individuals from their teeth, either by comparison with antemortem dental records or to known DNA samples, has been elaborated. However, this approach is not practical in identifying the edentulous. A useful method of identifying edentate individuals is by examining the palatal rugae pattern. The rugae pattern on the deceased’s maxilla or maxillary denture may be compared to old dentures that may be recovered from the decedent’s residence, or plaster models that may be available with the treating dentist.

Palatal rugae are ridges on the anterior part of the palatal mucosa on each side of the mid-palatine raphae, behind the incisive papilla (Fig. 21-6). These asymmetric and irregular ridges are well protected by the lips, cheek, tongue, buccal pad of fat and teeth in incidents of fire and high-impact trauma. Furthermore, Muthu, Subramanian and colleagues have found that palatal rugae can also resist decomposition to an extent. Rugae pattern, like teeth, are considered unique to an individual. They seldom change shape with age and reappear after trauma or surgical procedures.

Classification of Palatal Rugae

Attempts to categorize palatal rugae have spanned almost one hundred years. While many authors have suggested diverse classifications, the one suggested by Lysell is quoted most often. He measured rugae in a straight line, from their origin on the medial side to terminus on the lateral, and divided them into three types:

(Rugae < 2 mm is not taken into consideration).

This is a rather simplified picture of the intricate form that rugae usually present. Therefore, Thomas and Kotze have further categorized the various patterns of primary rugae as branched, unified, cross-linked, annular, and papillary. Other authors, such as Kapali and associates, have grouped the rugae according to shape as straight, curved, wavy, and circular.

Analysis of Rugae Pattern

Thomas and van Wyk have manually traced rugae patterns from post- and antetmortem dentures on to clear acetate (transparent plastic sheets) and then superimposed these tracings on photographs of plaster models. More recently, Limson and Julian have developed a computer software program which makes use of the principle commonly employed in fingerprint analysis. The method used digitized images of the palate on which characteristic points were plotted on the medial and lateral extremities of all rugae (Fig. 21-7). The plotted points were assessed by the software program and the information stored sequentially, corresponding to the pixel position. These researchers obtained up to 97% accuracy in identifying individuals in a simulated post- and antemortem comparison of the palatal rugae. Significantly, in their analyses, the authors have bypassed any form of classification suggested previously. In fact, Thomas and Kotze state that, considering the complex nature of rugae patterns, a universally acceptable classification may not be feasible and, as long as the technique used to compare the rugae is accurate, one need not conform to a particular classification.

Furthermore, a recent study by Ohtani and coworkers suggests that high accuracy rates in postmortem identification from palatal rugae can be obtained using straightforward visual comparison of post- and antemortem rugae patterns obtained from dentures (Fig. 21-8), and neither a classification protocol nor computeraided method is mandated. These authors did, however, infer that more complex the rugae pattern, greater the tendency for non-identification.

Dental Profiling

To pinpoint identity of the dead is possible when some form of antemortem information is available. But, as is seen from time to time, circumstantial evidence may not be available to give an indication about the putative identity of the deceased and, consequently, dental records are not traceable. This could be the case in skeletal remains recovered in an isolated area and with no proof of identification. Such cases warrant building a postmortem profile for reconstructive identification. Dental profiling includes extracting a triad of information—the decedent’s ethnic origin, sex, and age. According to Pretty and Sweet, ‘the information from this process will enable a more focused search for antemortem records’.

Identifying Ethnic Origin From Teeth

Physically, humans are a diverse species. This diversity is the result of genetic influences as well as environmental factors such as climate and geographic location. Therefore, the people of the world look different. Traditionally, the human species has been categorized into three ‘races’—Caucasoid, Mongoloid and Negroid. This classification, however, does not reflect human variation. Moreover, Relethford has emphasized that the concept of ‘race’ is rather ambiguous. Hence, it may not be an appropriate classification and has been discarded by biological anthropologists. Scott and Turner have divided humans based on geographic origin, which is the accepted approach today. Human diversity permeates to dental morphology as well, and dental anthropologists have cataloged this diversity. As a result, it is possible to identify an individual’s ethnic origin based purely on the dentition.

Genetic and Environmental Influences on Teeth

Teeth have proven to be significant in the study of human variation. Scott and Turner suggest that characteristic dental features have evolved over time as a result of genetic and environmental forces that influenced different population groups. Dental features have a complex mode of inheritance and are a combination of hereditary factors and environmental effects to which a person is exposed. As a result, today, different populations show considerable diversity in their dentition. For population identification, those dental features that have a stronger genetic and weak environmental influence are useful.

Dental features used to describe population differences are broadly categorized as metric (tooth size) and non-metric (tooth shape) traits. Metric traits are based on measurements, and non-metric traits defined in terms of presence (or degree of expression) and absence of a particular feature, for example, whether Carabelli’s cusp is present or not. Townsend cites numerous studies which indicate metric traits as being considerably influenced by intraoral environmental factors (e.g., missing lateral incisors cause compensatory increase in central incisors; space constraints in the jaws result in compression of third molars). On the other hand, nonmetric traits are more heritable and, therefore, dependable in establishing the population group to which an individual belongs.

Non-metric Dental Traits

More than 30 non-metric traits of the tooth crown and root have been described and analyzed in detail by Scott and Turner. Data exist for Indians for only a few features and these have been obtained from the preliminary studies of Vijapure and coworkers, and Angadi and Acharya, on a sample of 105 heterogeneous subjects. The following is a description of these traits:

Four-cusped Mandibular Molars

Conventionally, the mandibular first molar is considered to have five cusps while the second molar is regarded as having four. However, the distal cusp may be absent on the first molar and/ or expressed on the second molar. Therefore, both first and second mandibular molars are studied for the absence of the distal cusp. The frequency of four cusps is 11% for first molars and 90% for second molars in the preliminary Indian sample.

Table 21.1 reveals differences between populations from various regions of India for some of the features described above. Dissimilarities exist between different regions of the world, particularly between the major subdivisions of humankind, namely Eurasians, Africans, East Asians, and Native Americans. The range of dental variation among humans, however, is so great that several non-metric traits must be considered together before concluding on ethnic or population origin. Of the preceding features, some have aroused great interest owing to their high frequency in certain populations, while the occurrence of others is uncommon and, in some instances, rare. One must bear in mind that the high and low incidence of a non-metric trait is equally important in identifying a particular population/ethnic group. For example, people of European, West- and South-Asian origin (Eurasians) may exhibit four-cusped lower first molar, Carabelli’s cusp and three-cusped upper second molar in relatively high frequency, but features such as shoveling and Y-groove pattern do not occur often among them. On the other hand, four-cusped lower second molar is infrequent while shoveling and three-cusped upper second molar is commonly seen among East Asians. One is advised to remember, however, that the frequency of occurrence of many non-metric traits overlap in different population groups. Therefore, the use of such morphological characters for identification should be used carefully and judiciously.

Sex Differentiation

Assessing the sex, or sexing, of unknown human skeletal remains is the second step in the triad of building a dental profile. Sex can be assessed based on data from morphology of skull and mandible, tooth measurements and by analyses of DNA from teeth.

Sexing from Craniofacial Morphology and Dimensions

The use of morphological features of the skull and mandible (Table 21.2) is a common approach used by anthropologists in sexing. A number of features are known to show variation between the sexes. However Botha and Chandra Sekharan, in separate studies, caution that most of these features are not reliable until well after puberty. Even then, no single feature is characteristic and the use of multiple features tends to be more accurate. Williams and Rogers found that sex could be predicted correctly in 96% of cases using different features of the skull and mandible. Furthermore, they observed that using a constellation of just six traits—mastoid process, supraorbital ridge, size and architecture of skull, extension of the zygomatic arch beyond the external auditory canal, nasal aperture and gonial angle (on the mandible)—the accuracy of sex determination was 94%. This indicates that craniofacial morphology can be used to determine sex of skeletal specimens with a high degree of precision. While some authors believe that skull traits are affected by changes in old age, Williams and Rogers found no such effect.

Table 21-2

Craniofacial morphologic indicators of sex


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Skull features Male Female
Size/architecture Big/rugged Small/smooth
Frontal and parietal eminence Small Large
Forehead Sloping

Jan 12, 2015 | Posted by in Oral and Maxillofacial Pathology | Comments Off on 21: Forensic Odontology
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