Clinical and Radiological Perspective
Forensic odontology is the branch of dentistry which deals with the law. The last half-century has seen forensic dentistry make tremendous progress globally, both in terms of research as well as application in routine casework. Forensic odontology primarily involves identification. Right through history, the human dentition has been used several times in identifying individuals. Harvey (1973) has traced one of the earliest recorded incidences of dental identification to 66 AD, when the severed head of the wife of Roman emperor Nero was identified by a rival from her black anterior tooth. In 1193 AD the Maharaja of Kannauj, Jai Chandra Rathor, was recognized by his false teeth following death in a battle. The English duke Charles of Burgundy, who also died in a battle in 1477 AD, was identified from his dental features courtesy, the court physician who recognized two recently extracted teeth (Furness, 1972). Paul Revere is credited as being the first dentist to identify a person from dental features (Luntz, 1970). He identified a friend—who died in the American Revolution in 1775—from a silver and ivory bridge prepared by him.
Subsequently, intermittent cases of forensic dental identification in 19th century Europe and America have been reported (Pedersen, 1965). However, Gustafson (1962) believed that the role of forensic odontology in human identification came to prominence toward the end of the 19th century after two major fires in Europe: the first occurred in 1881 when the ‘Ring Theatre’ in Vienna was destroyed during a performance with 449 casualties; and the second— the Charity Bazaar fire in Paris in 1897—resulted in 127 deaths. In both tragedies, dental features were used for identification. According to Harvey (1973), one of the dentists who assisted the identifications in Paris was a Cuban named Oscar Amoedo. In 1898, he authored one of the first books on forensic odontology, L’art Dentaire en Medicine Legale, and is considered a pioneer of modern forensic dentistry. It is noteworthy that Yasutami Kojimahara of Japan had published a similar work titled Dental Jurisprudence a few years earlier in 1894 (Suzuki, 1996). The routine use of dental evidence in human identification gained impetus during the 1950s and 1960s, and forensic dentistry gained organized status in 1972 with the formation of the International Organization for Forensic OdontoStomatology (IOFOS).
With the evolution of criminal investigation in the industrialized world, scientific methods of detecting both the victim and culprit in a crime concurrently developed. Fingerprinting was one such method—the dermal ridges on our fingers are so unique even twins do not share an identical pattern. The human dentition is considered to be as unique to an individual as fingerprints are. The adult dentition normally consists of 32 teeth of which some may be missing, decayed or treated. Effects of various environmental factors such as fluorosis may also manifest in the teeth. Hence, it is extremely rare to have two identical dentitions, and this concept makes use of identifying the deceased. Moreover, teeth are one of the most durable parts of the body and can withstand physical, chemical and biological insults. As a result, teeth can be used to build the profile of skeletal remains. For example, race and sex differences in tooth morphology are known to occur; age estimation using tooth eruption, calcification and histological methods is frequently applied. Dental age estimation gained prominence following a case in Britain in 1935, where the age of two badly mutilated bodies was estimated from the calcification of third molars (Taylor, 1963). This contributed to the eventual identification of the bodies using photographic superimposition. In an age when heightened social, emotional and legal importance is placed on identifying the dead, dental identification methods has great relevance.
Apart from identification, forensic odontology is applied in the investigation of crimes where traces of the teeth, such as bite marks, are observed. The ability to match a bite mark to the uncommon arrangement of the dental arch can prove important in investigating sex crimes and violent fights. It is interesting to note that as early as the 6th century AD, the Indian sage Vatsyayana had recognized the prevalence of bites during love-making. Consequently, he devoted an entire chapter to ‘love bites’, with its detailed classification, in the treatise Kama Sutra. The unique arrangement of the dental arch was recognized in medieval Britain during the reign of William I (1027–1087 AD), green wax seals with the impression of the king’s teeth were implanted on state documents to avoid falsification and indicate the authenticity of the seal.
The use of bite marks as evidence in court can be traced back to 1692 in the United States. Harvey (1973) cites a 1906 case where a burglar was convicted in Britain because his dental models fit the marks left in cheese found at the crime scene which was probably the first successful conviction based on bite mark evidence in Europe. Subsequently there have been numerous cases that made use of bite marks but, with varying degrees of success. Therefore, bite marks remained a contentious area of forensic sciences. However, over the latter half of the 20th century, bite mark procedures have greatly advanced and it is now routinely used in court proceedings of Europe, America and Asia Pacific. Its objective application as evidence in crime can have far reaching implications for the society in general and criminology in particular.
The potential of teeth as legal evidence has rendered forensic dentists as an integral part of the forensic team of experts. Interest in the subject is not only confined to specialist forensic dentists but also oral physicians and radiologists, oral pathologists, pedodontists, prosthodontists and forensic medical professionals. This chapter attempts to address relevant clinical and radiological aspects of forensic odontology and it is intended to further stimulate the reader’s inquisition in this fascinating area.
Identity refers to the characteristics by which a person may be recognized (Acharya and Taylor, 2003) and identification is the establishment of a person’s individuality. Accurate identification of the dead is required both for legal and humanitarian reasons (Brown, 1984). It enables the settlement of insurance and property, permits remarriage of the surviving spouse and facilitate last rites of the body in accordance with appropriate religious customs. Haglund and Morton (1994) believe that a majority of individual identifications in forensic settings are nonproblematic since most individuals die in the company of family and friends. These deaths may occur at home or in a hospital, allowing visual identification. However, in cases where the body is burned, traumatized or decomposed, visual identification can prove unreliable. Hence, Sopher (1972) believes that visual recognition and use of personal effects are the least dependable methods of identification in such circumstances. Therefore, the safest option is for the forensic expert to analyze physical features present in the body.
Every individual has a variety of physical features that include built, height, epidermal ridges and dental characteristics. Most of these, however, are prone to change over an individual’s lifetime. Epidermal ridges (which produce fingerprints) are exceptions but, like other soft tissues, are susceptible to postmortem decomposition. Teeth are considered as the hard tissue analog to fingerprints and gain importance in identification as the time period since death increases. Although teeth are susceptible to disease during life, they are the most durable part of the body after death. Apart from teeth being relatively resistant to postmortem change, practically all materials used by the dentist are also resistant to postmortem destruction. Therefore, the use of dental evidence is considered essential for establishing identity in traumatized, decomposed and incinerated remains.
The underlying principle of dental identification is that combinations of dental characteristics are never the same in any two individuals. Several authors believe that the human dentition is unique (Johanson and Lindenstam, 1961; Keiser-Nielsen, 1977; Fellingham et al, 1984; Phillips and Scheepers, 1990). Human beings normally have 32 permanent teeth which vary in morphology and arrangement. Although teeth are relatively resistant to environmental factors and postmortem proteolysis, during life they are susceptible to disease such as caries. As a result, teeth may have undergone treatment in the form of fillings, crowns, etc. Those teeth that cannot be restored may have been extracted and, thus, missing from the oral cavity. According to Keiser-Nielsen (1977), the number of combinations 16 missing teeth can produce is approximately 60 crore. Sixteen filled teeth produce a similar combination. Four missing and four filled teeth combined can produce about 70 crore combinations. Every tooth has five surfaces and taking the 160 tooth surfaces individually would produce astronomical variations. In addition to the features visible on oral examination, radiographs reveal distinct shape and outline of various restorations of the crown and root and anatomic features of the teeth and bone (Sopher, 1972). Hence, the permutations resulting from observing the teeth clinically and radiographically would be phenomenal. It has been calculated that there are 1.8 × 1019 possible combinations of 32 teeth being intact, decayed, missing or filled (Fellingham et al, 1984). Therefore, dental identity can be considered as the sum total of all characteristics of teeth and associated structures which, while not individually unique, equal a unique totality (Acharya and Taylor, 2003).
Having ascertained the value of teeth in identification and the principle for the same, one can proceed with the procedure. Dental identification may be required in establishing the identity of a single person, a small group of individuals or in large fatalities such as accidental or natural disasters. The method for the different scenarios is essentially the same and is addressed together in the following columns although, considering the magnitude of the latter, the approach may vary. The identification procedure includes a number of steps, namely:
To begin with, it is essential to collect all dental evidence from the dead body (Haglund and Morton, 1994). This may require the dentist’s presence at the site where the dead body is recovered (Brown, 1984). Dental evidence present at the site where the body was found may be overlooked and not recovered—decomposition and skeletonization often leads to loosening of teeth and the anterior teeth, which have conical roots, may get dislodged. Oliveira and associates (2000) and Duric and coworkers (2004) have reported that incisors, especially maxillary, are most prone to getting lost postmortem. Incinerated bodies have fragile bones and teeth, which can easily be mishandled by an untrained individual; trauma may result in scattering of dental evidence around a large area. Acharya and Taylor (2003) have found that the inability to recover complete and intact postmortem dental data can undermine successful identification. Therefore, to maximize success, one must try to recover all dental evidence that may be present at the site. Hence, care must be taken to document and photograph the scene at which the body is recovered; a forensic odontologist should be present to ensure proper search and recovery of all material of dental significance needed for identification.
The postmortem dental examination is usually conducted in a mortuary. Case numbers allotted to the body should be verified and entered in the modified Interpol postmortem dental odontograph, also referred to as the ‘pink form’ (Figure 1) before the commencement of examination. A visual appraisal of the body may enable preliminary assessment of the ethnicity, gender and approximate age of the victim. The body bag used to transport the deceased should be thoroughly searched for dislodged teeth or dental appliances. Postmortem dental examination is similar to routine examination of the oral cavity. All oral and dental features, including intact and missing teeth, caries and other pathology, restorations, attrited and rotated teeth should be carefully charted on the postmortem form. This will be the basis for later comparison and verification. Brown (1984) suggests that postmortem examination should be undertaken by dentists working in pairs—one examining and the other recording. The roles are then reversed and the procedure repeated ‘as an added check’. Any dental evidence missing should be reported to the forensic pathologist or accompanying law enforcement personnel. Subsequent dental evidence recovered must be labeled properly.
The dental examination must be complemented with postmortem dental radiography as this will reveal what cannot be observed clinically. Radiographic films may be stabilized in the mouth using readily available materials such as gauze or cotton rolls. Whenever possible, postmortem radiographs should be taken to replicate the type and angle of the antemortem radiographs (Goldstein et al, 1998). According to these authors, if the difference in horizontal angulation between the ante- and postmortem radiographs is more than 10°, comparison will not facilitate identification. However, changes in the vertical angulation or the focal point-film distance do not affect the outcome of comparison. Pretty and Sweet (2001) have suggested that ante- and postmortem radiographs could be marked using a rubber-dam punch to differentiate the two—‘one hole for antemortem films and two holes for postmortem films’. The exposure time may need to be increased or decreased respectively in bloated bodies recovered following drowning and in skeletal remains.
Dental records contain information on treatment and dental status of a person during life. These antemortem records can be obtained from the local dentist, specialist or hospital records. Whenever possible, the original records should be examined. Records include hand-written dental charts, radiographs, study casts and photographs. An individual may have visited more than one dentist for therapy and multiple dental records may exist. Relevant information from the dental records should be transcribed onto the modified Interpol antemortem odontograph (the ‘yellow form’) (Figure 2).
Contribution of dental records in successful identification depends on the availability of original records, their completeness and quality (Acharya and Taylor, 2003). By maintaining good dental records, dentists reflect their awareness and responsibility to forensic identification (note: quality dental records are also important as a counter to malpractice lawsuits). It is also important that these records are relatively recent—records made for a 6-year-old child may not be useful 20 years later in adulthood.
The comparison of known antemortem data with the obtained postmortem data is called comparative identification. Sholl and Moody (2001) have stated that ‘the basic principle of any method of identification is to determine that individual characteristics observed postmortem are congruent with those known to have been present in life’. Once the postmortem findings and antemortem records are available, the data can be compared. Comparison should be qualitative rather than quantitative in nature; it must also be systematic and methodical. Features compared include dental restorations, pathology, crown, root and pulp anatomy, associated bony structures, artifacts and dental anomalies. An individual with multiple dental treatment and uncommon dental features has a better probability of being identified than someone with no extraordinary dental characteristics.
Presence of restorations are an important component of comparative dental identification. Sholl and Moody (2001) have suggested that the incidence of restorative work among younger age groups in Europe and North America appears to be declining, probably a long-term benefit of fluoridation and improved oral hygiene. Hence, there may be the necessity to rely on other features of the dentition. Therefore, the authors examined whether radiographs with no restorations could be used in postmortem identification. Their results indicated that dental anatomy observable on the radiographs, especially ‘root morphology and alignment’, facilitated correct identification in more than 85% of cases.
Subject to the availability of adequate postmortem data and quality antemortem records, Haglund and Morton (1994) have stated that ‘the comparison and eventual dental identification are straightforward and routine’. These authors believe that the quality and quantity of information required for establishing positive dental identification has not been established. In fingerprinting, differences in the ante- and postmortem data rule out a positive match. This concept, however, does not apply to dental identification as long as the inconsistencies are explainable. For example, the postmortem data may reveal a restoration on a tooth but the dental records indicate that the same tooth is intact. This difference, however, can be explained since the restoration may have been placed on a date after the last available dental record. On the other hand, if the postmortem data shows an intact tooth but the same tooth is indicated as being restored in the dental record, this would probably suggest a mismatch. Having compared the ante- and postmortem data, one should address whether the similarities are significant and the differences can be explained. Based on this, a range of conclusions can be reached which have been modified below from McKenna (1986), Silverstein (1995) and Acharya and Taylor (2003).
The ante- and postmortem data have a high level of concordance but a lack of quality information precludes positive identification. Explainable differences may exist between the two sets of data and radiographic support is, usually, not available.
The ante- and postmortem data are in agreement but the available information is insufficient both in terms of quantity and quality. The available information neither permits a definitive identification nor enables the identity to be excluded.
It is necessary for the forensic odontologist to be absolutely certain for an identification to be ‘positive’. One also needs to remember that any attempt at establishing identity is addressed to the legal authorities. Hence, the report and conclusion should be as definitive and clear as possible.
Traditional methods of radiography involve the use of film. The advent of digital radiography over the past decade, which replaces the radiographic film with an image capturing sensor, presents certain advantages to forensic investigation. Since the images can be viewed immediately after exposure, the operator has the choice to either accept or reject the image depending on its quality. Further, postmortem images may be retaken to replicate the antemortem radiographic position and angulation. This could be particularly relevant in postmortem settings where access to radiographic processing may be unavailable or the ability to retake the radiographs of the decedent at a future date is unlikely. Hanaoka and colleagues (2001) have successfully used the technology in postmortem dental identification and predicted its routine application in the future. They have stated that receiving, sending and storing digital radiographs through computer networks is effortless. According to Hubar and Carr (1999) and Du Chesne and associates (1999), the radiographic image may be enlarged, rotated and its brightness and contrast modified. Several images may be viewed together which allow convenient comparison of ante- and postmortem images. ‘Subtle features difficult to visualize on conventional radiographs such as trabecular bone patterns are seen with greater detail digitally and may further help to corroborate identification of a decedent’ (Hubar and Carr, 1999). However, manipulations which distort the structures visible on the radiograph by changing their angular relationship are not admissible by the courts of law (Du Chesne et al, 1999). Hence, these authors have stated that it must not be the objective of postmortem radiology to manipulate the images ‘to such an extent that optimal or even misleading results are presented’. While it is reasonable to expect forensic experts to avoid such alterations on postmortem radiographs, one cannot be so sure about antemortem digital images. Therefore, the conclusions based on comparison of post- and antemortem digital radiographs may be brought into question by the courts of law, which will probably give greater weight to documentary evidence such as conventional radiographic films than electronic data files.
Examining dental remains may be challenging in cases of rigor, incineration and other circumstances. Described below are some techniques to overcome difficulties, as well as precautions to be taken while using them.
Limited opening of the mouth due to severe postmortem rigor will affect dental examination since access to the oral cavity is limited and viewing the dentition is impaired. In such cases, where the muscles are extremely rigid, the mouth will have to be forced open. The use of trismus screws (made from acrylic) for obtaining initial opening in the anterior dentition followed by Fergusson or Heister mouth gags to increase jaw separation at the posterior region has proven useful in the author’s experience. However, one must be careful not to fracture the teeth. Nakayama and coworkers (2001) have advocated an intraoral approach for myotomy of the temporalis muscle. They contend that mouth opening demands relaxation of the temporalis and, hence, its myotomy will facilitate easy dental examination. Their method prescribes an intraoral incision to expose the coronoid process followed by the insertion of a curved Cooper type scissors through the incision to dissect temporalis fibers that are inserted to the top of the coronoid process (Figure 3A, B). The deep fibers, which may also insert to the mandibular notch, are drawn forward with a channel retractor for dissection (Figure 3C, D). The myotomy is carried out on both the left and right sides.
Figure 3 (A, B) Intraoral approach for myotomy: when the temporalis is attached to the top of the coronoid process, myotomy is accomplished with scissors only; (C, D) in case the temporalis is attached both to the coronoid and mandibular notch, a channel retractor is inserted to draw forward the deep end of the muscle to facilitate dissection. (Reprinted from Nakayama Y, Aoki Y, Niitsu H, et al (2001), ‘Forced oral opening for cadavers with rigor mortis: two approaches for the myotomy on the temporal muscles’, Forensic Science International, Vol. 118, pp. 37–42, with permission from Elsevier)
Due to the fragility of dental tissues consequent to fire, it is essential to maintain their integrity during examination of charred human remains. According to Delattre (2000), ‘charred dental remains are by nature rather delicate’ and can crumble if not handled cautiously. The color of the teeth, apparently, gives an indication of its relative fragility— blackened teeth are less fragile than those that are ashen gray (the appearance of incinerated teeth is described later in this chapter). The lips and cheek may contract in pro—longed or intense fire and withdraw exposing the anterior teeth. As a result, these teeth are the most exposed to fire and the enamel and dentin on their anterior surface can simply crack off when touched. To prevent the loss of tooth structure, Mincer and associates (1990) have listed a variety of materials that can stabilize incinerated teeth. They endorse clear acrylic spray paint and cyanoacrylate glue as the best agents since these are readily available, economical, portable, permeate the teeth well and set fast. However, in their study, not all specialists surveyed considered reinforcing incinerated teeth essential. Many felt problems could be circumvented by very careful handling of the teeth or photographing the teeth prior to handling. Intraoral radiography without jaw opening can be accomplished by removing the tongue through the floor of the mouth and inserting the films through the opening. This has been referred to as the ‘tunneling technique’ by Griffiths and Bellamy (1993), who have also suggested the use of material such as bubble plastic or a sheet of foam to protect the fragile skeletal and dental remains during transportation.
Depending on the circumstances of death and condition of the body, the forensic dentist can decide to cut open the soft tissue of the cheek to reach the teeth, or remove the jaws entirely. Resected jaws are easier to examine and radiograph. However, such ‘invasive’ procedures can pose obstacles, especially when the body needs to be viewed by relatives. Furthermore ethical and legal hurdles may be faced. Therefore, one must consider jaw resection as a last option and obtain prior permission from the forensic pathologist.
Tooth colored restorations such as composites and glass ionomers may be missed during examination. These can be disclosed using dyes such as mercurochrome or tinted benzalkonium chloride, which are applied on the teeth with cotton swabs. However, using dyes may leave the oral cavity stained and messy (Clark and Meeks, 1989). Therefore, Carson and colleagues (1997) have suggested the use of commercially available alternative light sources. They discovered that tooth colored restorations are best revealed at wavelengths of 415–530 nm. This range of wavelength also revealed restorations when the teeth were burnt, although standard UV light (350 nm) may have more practical value in fire-damaged bodies.
The identification and recovery of burnt teeth subsequent to accidents, arson or terrorist activities—where human remains may only be recovered in parts—can assist in establishing the origin of the remains and help reconstruct the scene.
Muller and associates (1998) have undertaken one of the few detailed works on changes that teeth undergo when exposed to high temperatures. They observed that enamel shows crazing (fine surface cracks) at 150°C but retained its normal color although at 200°C, enamel loses its gloss. Further increase in temperature causes more crazing— initially over the neck, then more coronally—followed by a few frank cracks.
Initial separation of enamel from dentin occurs at 400°C and the enamel shell separates totally at 450°C. At 500°C, Harsányi (1975) has observed deep longitudinal furrows on the crown which almost divide it into several pieces. At this temperature, the pulp chamber and root canal are preserved and not narrowed. Above 500°C, the crown undergoes fragmentation and consistently becomes smaller with further rise in temperature. The narrowed cavities of the pulp chamber and root canal are recognizable even at 1,100°C.
The coronal dentin is exposed at 450°C (following total separation of the enamel shell). Cracks appear at 600°C with disintegration from 800°C onward. While enamel is converted to powder, dentin is not. This has been attributed to hypermineralized pretubular zone of the dentin. Myers and colleagues (1999) believe that the mineral content of dentin, located within its organic matrix composed of type I collagen, helps stabilize the collagen against thermal denaturation and shrinkage. The color changes in the crown and root at different temperatures has been demonstrated by Muller and associates (1998) (Table 1). However, these authors have cautioned that in real-life scenarios, it may be much more difficult to observe the color changes since teeth found at the site of fire need to be carefully cleaned. They added that ‘the presence of a superficial metallic layer, resulting from the dry distillation of organic matter, can lead to observational errors’.
|150||Crown||Normal color and shiny appearance|
|Root||Off-white to light yellow|
|200||Crown||Dull, light brown surface|
|300||Crown||Light brown to grayish with dark brown spots|
|500||Crown||Enamel is dark brown or gray; dentin is gray|
|600||Crown||Dark gray enamel and blue-tinted gray dentin|
|Root||Blue-tinted gray with white spots|
|700||Crown||Dark gray enamel and blue-tinted white dentin; the cusp tips are blue|
|Root||Blue-tinted white or white only|
|800||Crown||Dark gray enamel with white spots; white dentin|
|Root||White with gray spots|
|Root||White with dark gray or black spots at CEJ|
|Root||White with pink tinge at apex|