General Dentistry

An introduction to forensic dentistryDavid K, Whittaker*

Denial .-iciencc has much to offer law enforcement agencies in the detection and solution ofcrime. The permanent teeth develop throughout the fust two decades of life, and physiologicvariations, pathoses, and the effects ofdental therapy may be recorded in the hard tissues ofthe remaining dentition throughout life and beyond. It is the role of the forensic dentist to ex-tract this information and use it in the identification ofthe unknown body. The teeth may alsobe used as weapons and. under certain circumstances, may leave information as to the idenliiyof Ihe biter. Analysis of bite marks is the second major responsibility of the forensic dentist.The general practitioner has a major role to play in providing ¡he accurate dental records onwhich mtich of forensic activity is hased. (Quintessence h\i 1994:25:723-730.)

Introduction

A number of essential characteristics of the humandentition separate humans from other animals and pro-vide a certain uniqueness. The first of these results fromthe intermixing of genetic racial characteristics thathave upset the natural balance between size and shapeof the leeth and those of the supporting jaw bones. Thesecond is the modern chemical and structural modifica-tions of teeth resulting from disease processes or the at-tempt to cure such disease.

Dental treatment itself is the biggest single contribu-tor to the uniqueness of an individual's dentition and,along with developmental characteristics, is the key toenabling identification of the dead from an examina-tion ofthe oral cavity. Another important feature oftheteeth is that they are the most indestructible part of thehody and exhibit the least turnover of natural structure.They therefore not only survive death but also remainrelatively unchanged thereafter for many thousands ofyears (Fig 1). Forensic dentistry relies on this inde-

Rcader in Oral Biology, Adviser in Foiensic Dentistry to theHome Office, Department of Basic Dental Science, DentaiSchool, University of Wales, College of Medicine, Healh Park,Cardiff CF4 4XY Wales.

struct ibi I ity, and its scientific advancement is designedto extract increasing amounts of identifiable informa-tion from oral structures, which, more than any otherpart of the body, mirror the fortunes of the individualconcerned. Identification of a deceased individual or ofa mark left by his or her teeth is the purpose of the fo-rensic dentist. Reduced to its simplest terms, forensicdentistry has only two aims: the relatively simple one ofidentification of the dead and the more complex one ofidentifying an assailant who has used his or her teeth asweapons,'

Identification

In civilized societies, it is socially and legally essentialto identify the dead before a death certificate can be is-sued. Most human corpses are identified by close rela-tives or acquaintances who recognize facial appear-ance. In a small percentage of cases, postmortem putre-faction or severe damage to facial features may rendersuch identification impracticable or undesirable, andfingerprints and palm prints may be used. Natural orintentional loss of this information leaves a small num-ber of cases where identification by traditional meth-ods is impossible. It is not reliably known how manysuch cases occur in Ihe United Kingdom annually, but itis about 200 to 300, excluding abnormal situations, suchas mass disaster, when this figure may double from onesingle event.

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General Dentistty

Forensic dentistry does nol offer an objective meth-od of identification comparable to either the finger-print or, more recently, the use of DNA lechnology, butit is relatively inexpensive, is capable of rapid results,and at best produces a virtually certain identification.Even when data are sparse, it may result in putativeidentification that can later be confirmed by more sci-entific techniques.

Species, sex. and race determination

Species determination usually presents no difficulties,unless only fragmentary evidence is found al the sceneof a crime. There may be a fragment of mandible bear-ing teeth or, at worst, a small fragment of a single toothno more than a few millimeters in size, 'ITie traditionalmethod of procedure in these circumstances has beento examine the fragtnented tooih or bone, using com-parative dental anatomy to determine the species of or-igin. If this is not possible from ihe shape of the frag-ment, the enamel may be examined with light or elec-tron microscopy because the arrangement of the ena-mel rods or prisms differs, for example, between pri-mate and nonprimate tissues (Fig 2),

More recently, it has been shown that dentinal tiuidscontain specific species information. These lluids maybe compared using counter-current electrophoresiswith artificially raised species-specific antisera,' Thistechnique can determine species up to at least 12months after death (Fig 3),

In a similar manner, remnants ot cells from frag-ments of bone or teeth may be examined for the pres-ence or absence of Barr bodies or the sex chromosomestatus of the cells,•* These teehniques have also beenshown to be applicable for al leasl 12 months afterdeath.

Racial determination from the skull and teeth is no-toriously difficult, but separation into the main Cauca-soid, Negroid, and Mongoloid racial groups may bepossible using cranial and facial morphology. Many ra-cial traits have also been described in individual teeth.For example, the evaginated odontome on the occlusalsurface of premolars in Chinese persons and the shov-el-shaped incisor of the Mongoloids might eiiminate aCaucasoid origin.

Facia! reconstruction

The average thickness of soft tissues overlying variousparts of the face is a rather stable characteristic. A rep-resentation of facial soft tissues can therefore be recon-

slructed into an unidentified skull, using traditionalsculpture methods or the application of computer tech-nology. The resulting facial model may be exhibited inIhe media and may result in Ihe recall of a name by amember of Ihe public (Fig 4), Putative identificationcan be used in Ihe search for previous denial recordsIhat may confirm the identity ofthe deceased.

Age determination at death

A very important stage in identification is an accuratedetermination of the age of the body. Fortunately, thehuman dentition follows a reliable and predictable de-velopmental sequence beginning about 4 months afterconception and continuing to the beginning ofthe thirddecade of life, when development of all the permanentteeth is completed. Radiographs of the jaws will indi-cate the extent of mineralization within each individualtooth type, enabling age at death to be determined towithin a few months in infants and to within a few yearsin teenaged specimens.

An important medicolegal problem is whether thedeceased infant was slillburn or survived birlh with anindependent existence. In the absence of soft tissues, asingle primary tooth may be extracted, sectioned, andexamined microscopically. The physiologic trauma ofthe birth event will leave a pemianent biologic markerin the hard tissues of the developing child at birth, andthis may be visualized with scanning electron microsco-py (Fig 5), This so-called neonatal line may be of ex-treme medicolegal importance in these cases,''

The roots of the teeth in the permanent dentitioncontinue to grow for some years after eruption and, inthe case of the third molar or wisdom toolh, growth ofthe root is not completed until the end of the seconddecade of life. Age at the lime of death may thereforebe determined from radiographs up to this stage,̂

Individual leeth erupt itito the oral cavity in a chron-ologic sequence that is less reliable than the develop-mental status; however, in younger people, a reason-able determination of age al death is possible from thisfeature alone. Wide racial and sex variations may needto be taken into account. The last of the permanentteeth erupt at around 18 years of age. From 20 years ofage to old age, age determination at death becomesmore difficult and is dependent on rather more subtlechanges, which, fortunately, are permanently retainedwilhin the hard tissues of the teeth. They may be usedto determine the age of modern-day material and evenmaterial from the early Egyptian dynasties (Fig 6). Themost important and useful change in the teeth is a poor-

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General Dentistry

Fig 1 Preservation of teeth in mandible of Tabun manabout 35,000 years old. (Courtesy of Natural History Mu-seum, London.)

Fig 2 Scanning electron micrograph of decussation ofprisms (rods] in bovine enamel.

Fig 3 Counter-current eiectrophores/s for studying toothfluids.

Fig 4 Partially reconstructed head for identification.(Courtesy of Mr R. Neave.)

ly understood biologic phenomenon whereby the tu-hules within the Toot apex become progressively min-eralized as age progresses.'' This mineralization altersthe refractive index ofthe dentin, rendering it transpar-ent when examined microscopically. The extent of thisroot transiucency may be determined by computermapping of serial hard tissue sections of the tooth' (Fig7). Regression tables prepared from large numbers ofteeth of known age have been used to show that it ispossible to determine the age of an unidentified bodywithin about 7 years ofthe correct age at death.

Masters,'̂ working largely on animal material, has re-cently laid the fottndations for a more objective meth-od of age determitiation. This depends on the findingthat amino acids are built into the collagen as opticallypure enantiomers of the S-aspartic acid type. Once thetooth has mineralized, these amino acids cannot be re-placed. With the passage of time the aspartic acid enan-tiomer slowly undergoes racemization producing theopposite enantinmer, R-aspartic acid. The rate atwhich this change occurs has heen determined, and bymeasuring the ratio of right-handed to left-handed

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General Dentistry

Fig 5 Scanning eiectron micrograph of neonatai iine inhuman primary enamel.

Fig 6 Three-dimensionai radiographie computed image ofmaxiilary molars from an unopened Egyptian mummy.

Fig 7 Dye-imbibed patent dentinal tubules in human den-tin, Uncolored tubules are sclerotic and related to age.

Fig 8 Regression graph of D-aspartic acid related to ageof donor.

Fig 9 Scanning electron micrograph of bur cuts in bumanleetb relating tooi mariis to the type of instrument.

Fig 10 Intraorai tattoo.

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General Dentistry

enantiomeric residues in the tooth, the forensic dentistcan determine the age ofthe individual at death (Fig 8),

The poicniial lor application of this mcthodolog^y inthe archeological and forensic fields is immense. In itspresetit, rather crudo, form, the technique is at least asaccurate as any other biologic technique and will al-most certainly become the method of choice for deter-mining the age of unknown individuals by means of theteeth.

Medical and dental liistorv

Once the physical characteristics of the deceased havebeen established, the forensic demist embarks on a de-tailed examitiation ofthe mouth. Unlike soft tissne sur-gery, the results of which may be finally obliteratedduring the healing process, treatment of the hard tis-sues does not, on the whole, repair itself. Therefore, anititervention even during childhood may remain visiblethroughout the life ofthe individual and beyond.

Because the teeth are subject to genetic variation,the examination of the mouth will usually commenceby a description of dental anomalies such as missingteeth, misplaced or rotated teeth, unusually shaped orsized teeth, and supernumerary teeth. The status ofeach tooth with respect to restorations that have beenplaced will be recorded. The exact design and style ofeach restoration may not only reveal the country inwhich the dentist was trained but may even reflecttraining in different centers in the United Kingdom(Fig 9), A knowledge of these variations will not direct-ly identify the body but may well identify the origin ofthe dentist. In certain circumstanees it may be neces-sary to remove restorations and to analyze them chem-ically and physically to determine their exact composi-tion.

Other aspects of therapeutic dentistry that may be ofimportance are the presence of orthodontic appliances,the design of which may be an indication of origin. Ifthe body possesses either a partial or complete denture,then the design atid construction technique, not tomention the possibility of labeling with the patient'sname or Health Service number, may be important in-dicators of identification. Even soft tissues may some-times carry the owner's visiting card (Fig 10),

Time elapsed since death

Estimations of this nature, so beloved of writers of de-tective fiction, are in reality extremely difficuh. Den-tistry, distinct from forensic pathology, has htde to of-

Fig 11 "Pink teeth" in a drowned cadaver.

fer. but ifdeath has occurred, the teeth ofa corpse maylake on a distinctive purplish pink color'' that is due toaccumulation of blood breakdown products in the den-tinal tubules (Fig 11), It appears to take from 7 to 14days before discoloration becomes apparent so thismay give some gross indication of time of death.

More useful indications may be related to previousdental treatment. If a tooth was extracted before death,the degree of healing ot the socket can be studied by us-ing sections and polarized light microscopy. The pres-ence of woven or healing bone in an apparently healedarea of Ihe jaw indicates that the tooth was probablyextracted about 1 year before death. Subsequent dis-covery of dental records indicating an extraction on aparticular date will enable the approximate time ofdeath to be estimated.

Comparison with previous records

The examples cited give some indication of the breadthof information that may be acquired from study of thedentition. This information allows the preparation of athumbnail sketch of the character and previous historyof the deceased. Final identification will have to rely oupreviously produced antemortem dental records. Itthen beeomes a relatively simple procedure to comparethe information derived in the postmortem situationwith that present in the antemortem records.

The identification techniques arc applicable to deathof a single individual but also are extremely importantafter a mass disaster, in which there may be severe mu-tilation or burning of bodies, particularly in a high-speed air disaster, when severe disintegration of bodiesmay occur,'''The techniques are similar but the logistics

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of dealing with up to 400 bodies arc considerable andform a subject in their own right. Suffice it to say that inmost air disasters, 60% to 70% of all individuals areidentified solely or partly through dental evidence. Fo-rensic dentistry is the single most important techniquefor identification in these circumstances, and accuratedental records made and retained by the dental practi-tioner may be crucial in these procedures.

Bile mark analysis

Although in a crime involving shooting it may be pos-sible to determine that a bullet was fired by a particularweapon, it may be more difficult to relate the weaponto the assailant. When the teeth are used as weapons,they are not so easily disposed, and they can be relatedto the person inflicting the wound. Bite marks occurunder various circumstances, usually associated withmnrder or rape with sexual motives, but are also asso-ciated with nonaccidental injury in children. Bitemarks may be identified on both the living and thedead, and in the latter case may be antemortem or post-mortem injuries."

Bites in human ¡issue

The force required to penetrate the skin is consider-able, and bites showing laceration ofthe tissue are nec-essarily aggressive in nature. The assailant may suckthe soft tissues into the mouth so that images ofthe pal-atal surfaces of the teeth as well as of the incisai edgesmay appear,'- The forces required may result in pcte-chial hemorrhages in the center of the wound. All ofthese features must be analyzed in describing the mark.Less aggressive bites may not penetrate the skin butwill leave a partial or complete oval of marks relatingmainly to the anterior teeth {canine to canine). Duringbiting the victim (if alive) and the assailant will fre-quently be struggling so that the teeth may producescrape marks before the tissue is finally bitten.

The tissue is flexible and is distorted during the bite.If the bite is on a living person there will be poslinjurychanges in the tissue, resulting in bleeding, swelling,and discoloration. In a dead individual there may bepostmortemchanges that complicate the analysis ofthemark. All of these factors must be considered andmake bite mark analysis the province of the experi-enced forensic dentist.

It is important to photograph the mark with stan-dardized techniques,'' Special scales with imprintedmarks have been produced for this purpose to allow the

degree of distortion of the photographic image to bedetermined. Sometimes it is necessary to rephotographthe mark at hourly intervals because there may bechanges as time progresses. The type of dentition thathas made the mark should be determined from theintercanine width, the size of arch curvature, the pres-enee or absenceof marks within the arc of the bite, andfine detail such as rotated or damaged teeth. A reportshould be prepared at this early stage before any sus-pects are interviewed so that no bias is introduced intothe analysis of the mark.

Once a number of suspects have been produced, im-pressions and study casts of their dental arches are pre-pared according to standard dental procedures. It isnecessary to obtain the written permission of the sus-pect, who has been informed that the evidence may heused in a court of law. Transparent photographic over-lays (Fig 12) are prepared from these study casts at thesame scale as the photographs of the original bitemarks. These casts are located over the bite mark andarranged so that a jury can compare the characteristicsof the dentition and the bite mark.

Unless the bite is unusually clear and possesses char-acteristics that are unlikely to occur in more than onedentition, it is safer to exclude suspects through thesetechniques rather than to implicate them. There are,however, situations where the details within the markare so conclusive that a jury would be advised that noincompatibility exists between the dentition of the de-fendant and the mark on the victim.

Thirty-two human bite marks (Fig 13) were inflictedon the body of a young man who was subsequentlymurdered. The detail within this mark was such that itwas possible to distinguish each individual tooth, thecavities and fractured edges in the individual teeth, andthe fact that the mandibular teeth were heavily wornand had at least one space between two of the teeth.The bruising caused by suction on the tissue can also beseen in thecenterof the arcade of marks. Bite marks inhuman tissue can range from clear examples, such asthis, to faint bruising. In the latter case it may be pos-sible to determine that a human bite has occurred butimpossible to match it to any particular suspect.

Bites in other materials

Criminals may, from time to time, leave their dental sig-nature in bitten apples, chocolate, cheese, or otherfoods left at the scene of a crime.''' There are cases inwhich assailants have bound victims with adhesive tapeand torn off sections of the tape with their teeth, leav-

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General Dentistry

Fig 12 Transparent overlay for matching dentitions with abite mark.

Fig 13 Human bite with overlay titted to marks trommandibular teeth.

ing identifiable bite marks on the tape. The same prin-ciples of analysis apply as in the case of tissue bites, butbites in artificial substances or foods can often yieldmore information because of the lack of distortion ofthe material and its ability to make a good impressionof the biting edges of the teeth.

In all types of bites, it is important that, before thematerials are handled, swabs are taken to tesl for pos-sible salivary contamination because this step may re-veal the blood group of the biter. If the saliva containsintraoral cellular material, DNA analysis may bepossible.

Nonhuman bites

Bites may be left on human victims or on artifacts byanimals. Most often in the United Kingdom these ani-mals are dogs, cats, or rodents. The character ofthe biteis dependent on the dentition of the animal: the classiccarnivore bite is four puncture wounds produced by thelarge and aggressive canine teeth of these animals (Fig14). Rats may produce multiple small lacerations fromindsor teeth or make larger lacerations by slashingtheir razor-sharp incisors from side to side, '

Conclusions

Forensic dentistry is still in its infancy and may be con-sidered more of an art or craft than a science. Areas ofdevelopment include the increasing understanding ofthe biologic nature of the tissues involved as well as thefunctional activtty of the masticatory apparatus underboth normal and abnormal conditions. There are hun-dreds of cases each year in the United Kingdom of both

Fig 14 Dog bite in a victim's leg.

identification problems and of bite mark events. Fromthese cases, experience is being acquired and of appli-cation of biologic and physical sciences to ihe subjectcan be expected to yield new techniques that are cur-rently only theoretical concepts.

It is important that for the development oí forensicdentistry, practitioners retain a healthy degree of scep-ticism of their abilities: in recent cases forensic sciencein general has been shown subsequently to be subjectto misinterpretation, Tliere is no more important layaudience Ihan the jurors in a murder trial, and theymust not be given the impression that the forensic den-tist is a Sherlock Holmes or a Hercule Poirot,

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References

1. Whittaker DK. MacDonald DG, A Colour Alkis of t-ortnsicDotitis:ry, London: Wolfe Medical, t')89;Çi.

2, WtiUlakcr DK. Rawlc LW, The etfect oí conditions of putrefac-tion on species determination in human and animal toetli.ForeDs Sei tnt l'J87;35:209-2t2.

i. Whittaker DK, Ltewelyn DR, Joncs RW. Sex determinationfrom necrotic pulpal tissue. Br Dent J m?."); 139:403-405,

4. Whittilker DK, Richards D. Scanning electron microscopy ofthe Tieonatat line in human snamel. Arch Oral Biol lUTS:23:45-50.

5. Kumar CL. Sridhar MS. Eslimation of the age of an individualbased on time; of eruption of permanent teeth. Forens Sei Int1990:4S:t-7.

6. Sotheim T, Dentat root transiucency as an indicator of age,Scand J Dent Res 1989:97: t89-t97.

7. Drusini A, Calliari I, Voipe A. Root dentin transparency: Agedetermination of human Leeth using computerized densitomet-ric analysis. Am J Phys Anthropol 19Q1 ;85:25-30.

8. Masters PM. Age at death determinations tor autopsied re-mains based on aspartic acid racemization in tooth dentin: Im-

portance of postmortem conditiuns. Forens Sei Int 1985;32:179-184.

y. Beeley J, Harvey W. Pink teeth as a poslmortem phenomenon.J Forens Sei Soc 1973:13:297-305.

to. Muhlcmann HR, Steiner E, Brandestini M. Identification ofmass disaster victims: Swiss identification system. J Forens Seil<J7y;24:173-lKI.

t l . Allison RT, Whiltaker DK. Use of benzidine for histologicaldemonstration of haemoglobin in human hite marks. J ClinPalhol 199U;43:6œ-603.

12. Harvey W, Millington P, Barbenel JC, Evans JH. Experimentalhuman tiite marks. In: Harvey W {ed). Dental Identificationand Forensic Odontology. London: Kimpton, 1976:124.

13, Robinson E, Wentzel J. Tonelinc bite mark photography.JForeDsSei 1992:37:195-207.

14, Rudland M. The dimensional stability of bite marks in applesafter long-term storage in a fixative. Med Sei Law 1982;22:47-50.

15. Wykes WN, Rat bite injury to the eyelids in a 3 month old child.Br J Ophthalmol 1989;73:202-204. D

<30 Years of Resear(hExtensive pubiished iiterature.*Bibliography auailabie uponrequest.

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730 Quintessence International Volume25, Number 10/1994