The value of dental characteristics to identify deceased individuals has been well recognized since the late nineteenth century. Interestingly, the use of dental science to aid the identification of the deceased appears to have been originally driven by external agencies, for instance police, coroner’s and courts rather than from within the dental profession. Once the value of forensic odontology was recognized by dentists, the obligation to demonstrate efficacy through scientific rigor was embraced and has seen the evolution and maturity of what is now regarded as a specialty within the dental profession.
Teeth aren't fingerprints; they aren't inherently unique from birth. When teeth grow in, or erupt, they do so differently in each person. Teeth grow an average of 4 micrometers per day, so it's possible to give a rough age estimate based on teeth. It can also be possible to distinguish ethnicity from the teeth. Some Asians and Native Americans have incisors with scooped-out backs.
The patterns of tooth wear also vary and can change over time. Not only can people be identified by their teeth, you can also learn a lot about their lifestyles and habits by the state of their teeth.
Although each type of tooth has a different name, we have multiples of some types of teeth. For example, a full set of adult teeth includes two upper central incisors and two upper lateral incisors. Therefore, each individual tooth needs its own designation. There are dozens of methods for labeling teeth in use, but the three most popular methods are the Universal System, the Palmer Method and the FDI (Fédération Dentaire Internationale) World Dental Federation notation.
In the United States, most dentists use the Universal System. In this system, each of the 32 adult teeth is assigned a number. Number one is the upper right third molar, while number 32 is the lower right third molar. The 20 deciduous, or baby teeth, are designated by the letters A through K or the number-letter combination of 1d through 20d.
Some teeth, like molars, have multiple surfaces too. Each of these surfaces has a name. The center of the tooth is the biting surface, known as the occlusal. This surface has two elements: the cusps, or raised parts, and the grooves, or indentations. The mesial surface of the tooth is toward the front of the mouth, while the distal is toward the back. The side toward the inside of the mouth is the palatal surface on the upper jaw (lingual on the lower jaw). The tooth surface facing the cheek is the buccal. So if you get a filling on the distal of number 15, you'll know that means it's on the surface facing the back of the mouth on your upper second molar (or 12-year molar).
When you visit the dentist for a checkup, he or she uses a Universal System chart and makes a notation on each tooth to show variations such as chips and dental work such as fillings, crowns and bridges. The dentist also includes observations about the health of your teeth, like receding gums or signs of periodontal disease. Most dental visits involve taking sets of X-rays, which can also show work not easily seen, like root canals.
There is no database of teeth that corresponds with databases of fingerprints or DNA, so dental records are how forensic dentists identify the dead. Tooth enamel (the outer layer of teeth) is harder than any other substance in the human body, which is why teeth remain long after all other parts have decayed. Victims of fires are often identified by their teeth, which can withstand temperatures of more than 2,000 degrees Fahrenheit (1,093 degrees Celsius). Teeth that have been through especially intense heat are very fragile and may shrink, but they can be preserved with lacquer and used for identification as long as they are handled very carefully. Dental work, such as a partial or gold crown, will be distorted by fire but can still aid in identification.
To identify a person from his or her teeth, a forensic dentist must have a dental record or records from the deceased person's dentist. In the case of an incident involving multiple deaths, forensic dentists receive a list of possible individuals and compare available records with the teeth and find a match. Examining the teeth of an intact corpse often requires working in a morgue to expose the jaws surgically. Even if only a few teeth are available, a forensic dentist can still make a positive identification. The best comparisons come from X-rays, but even if those aren't available, notations on the tooth chart can tell the dentist if the teeth are the same.
Identifying an individual by his or her teeth without dental records is much more difficult. However, things like broken teeth, missing teeth and gold crowns might be recognized by the friends and family members of the deceased. Things about the biter's lifestyle can be determined by the teeth; a constant pipe smoker or a bagpipe player has a distinctive wear pattern. Dressmakers and tailors, who often put pins and needles in their mouths, may have chipped teeth.
In addition to the dental records, forensic investigators can retrieve DNA samples by extracting the pulp from the center of the tooth. Unlike the enamel, pulp can be damaged by fire and other conditions, but it can also last for hundreds of years. Dental identification is often the last resort, and it isn't always possible -- some people simply can't be identified.
Bite marks are tricky because they're about more than just the teeth. Time can affect bite marks, and so can movement and pressure. Bite-mark analysis is extremely complex, with many factors involved in a forensic dentist's ability to determine the identity of the perpetrator.
The movement of a person's jaw and tongue when he or she bites contributes to the type of mark that is left. Depending on the location of the bite, it's not typical to find bite marks where both the upper and lower teeth left clear impressions , usually one or the other is more visible. If the victim is moving while being bitten, the bite would look different from that inflicted on a still victim.
If an investigator sees something on a victim that even resembles a bite, the forensic dentist must be called in immediately, because bite marks change significantly over time. For example, if the victim is deceased, the skin may slip as the body decays, causing the bite to move.
The first step in analyzing the bite is to identify it as human. Animal teeth are very different from humans' teeth, so they leave very different bite-mark patterns. Next, the bite is swabbed for DNA, which may have been left in the saliva of the biter. The dentist must also determine whether the bite was self-inflicted.
Forensic dentists then take measurements of each individual bite mark and record it. They also require many photographs because of the changing nature of the bites. Bruising can appear four hours after a bite and disappear after 36 hours. If the victim is deceased, the dentist may have to wait until the lividity stage, or pooling of the blood, clears and details are visible. The bite photography must be conducted precisely, using rulers and other scales to accurately depict the orientation, depth and size of the bite. The photos are then magnified, enhanced and corrected for distortions.
Finally, bite marks on deceased victims are cut out from the skin in the morgue and preserved in a compound called formalin, which contains formaldehyde. Forensic dentists then make a silicone cast of the bite mark.
Forensic dentists use several different terms to describe the type of bite mark:
In addition, there are several different types of impressions that can be left by teeth, depending on the pressure applied by the biter. A clear impression means that there was significant pressure; an obvious bite signifies medium pressure; and a noticeable impression means that the biter used violent pressure to bite down.
A forensic dentist can tell a lot about the teeth of the biter based on the bite mark. If there's a gap in the bite, the biter is probably missing a tooth. Crooked teeth leave crooked impressions, and chipped teeth leave jagged-looking impressions of varying depth. Braces and partials also leave distinctive impressions.
Once investigators have identified a suspect, they obtain a warrant to take a mold of his or her teeth as well as photos of the mouth in various stages of opening and biting. They then compare transparencies of the mold with those of the bite-mark cast, and photos of both the bite mark and the suspect's teeth are compared to look for similarities. Bite-mark analysis has been in the news in recent years due to its controversial nature.
Dental identification plays an important role when identification of remains of deceased person is skeletonized, decomposed, burned or dismembered and is invalid by visual or fingerprint methods in case of traumatic deaths like burns, accidents, etc, when the bodies are mutilated beyond recognition. Also in cases of massive tissue injuries or in the absence of fingerprint records, or where the visual and fingerprint method of identification fails, dental records can prove to be the only help for identification. Another advantage of dental tissues is the fact that, they are often preserved after death, so incase of skeletonized remains, these prove to be a precious tool.
All mouths are different and the trained eye of the forensic odontologist will be able to offer a considerable amount of useful information. Most obvious will be to provide an accurate charting of the teeth and fillings present to compare with dental records of missing persons. This often leads to a positive identification. Despite recent advances in DNA technology, dental identification still offers a rapid and cost effective approach. The identification of remains by dental evidence is possible because, the hard tissues are preserved after death and can even withstand a temperature of 1600 degrees Celsius when heated without appreciable loss of microstructure, and the status of a person’s teeth change throughout the life and the combination of decay, missing, filling can be obtained from any fixed time. An opinion can still be offered on age, habits, oral hygiene, and individual features which may match with ante-mortem records. Where the subject has no teeth, useful information can still be gleaned from the study of any dentures and by X-raying the jaws and skull.
Odontological identification is based on systemic comparison of pre and post mortem dental characteristics of individual based on dental records and the supporting radiographs. But this technique is complicated by the trauma to jaws and inadequate ante-mortem dental information.
Dental identification can be divided into four types:
In many cases, dental identification, fingerprint, and DNA are most commonly used and often complement each other. It is important that the services of a forensic odontologist be sought early in these cases, as much time consuming police work can be avoided given a dental report early in the investigation.
Estimating chronological age of individuals with no or doubtful age documentation is a principal discipline in Forensic Odontology. Forensic age estimations in the living are requested in relation to age thresholds in criminal investigations, during immigration procedures, and for civil purposes. In addition, estimating age of unknown bodies facilitates a traced search for ante mortem data by narrowing the age interval of the search.
Dental age estimations are specifically based on age-related variables observed in teeth. The major age-related features observed in the dental variables are changes in the morphology or the development of the tooth and modifications in the biochemistry of tooth material. In forensic age estimations often dental age estimation methods are combined with methods based on non-dental variables.
Dental ageing technique can be broken down into two categories.
Tooth formation begins at a very early stage of life by six month. The sequence of formation and eruption of teeth with give a precise age estimation method. In this method, each tooth is scored based on its developmental stage and scores are compared with values corresponding to a particular age.
For example: a deciduous second incisor crown that is fully formed and is recovered adjacent to a deciduous second incisor crown that is only 3/4 complete suggest a single individual of age less than 6 months . But, if complete deciduous second molar is found in association with these 2 teeth, then it may represent that there are more than 1 individual. This is used if dentition is completed and not applicable if there is missing teeth due to cases etc.
Human dentition has 2 eruption stages and their associated ages. To assess the age of unknown individual, we can compare the postmortem radiographs of the individual to the eruption standards produced by the Schour and Massler .
Third molar emergence tends to be around 17-19 years of age. This tooth has high variations, may be completely developed but impacted or it may be completely absent. Only radiograph can be the give the accurate document of this tooth .
This technique was an alternative to the qualitative assessment where the length of tooth was measured
That occurs once the teeth have erupted and begin to wear down. There is an intuitive connection between tooth wear and age, as those with more wear tend to be older. We can use volume of pulp cavity because it’s seen that the volume of pulp cavity reduces due to deposition of secondary dentine with ageing .
Age estimation is the important part in forensic odontology because human dentition follows a reliable and predictable developmental sequence.
Sex determination is very important subdivision of forensic odontology, which plays a major role in identification of the unknown individuals in natural disasters; chemical and nuclear bomb explosion scenarios. It comes into picture when the evidence found at the scene of crime is a fragment of mandible or just a single tooth, which is of few millimeters in size. It is possible to determine species by dental tissues because the dentinal fluids contain special information, which can be compared and analyzed using counter current electrophoresis with artificially antisera.
It can be done by four methods :
Craniofacial morphology and dimension: The morphology of the skull and mandible, pattern formed by six traits those are mastoid, supraorbital ridge, size and architecture of the skull, zygomatic extensions, nasal aperture, and mandible gonial angle and Frontal sinus dimension are taken into consideration.
Sex difference in tooth dimension: Sex determination by measuring mesiodistal and buccolingual dimensions is most simple and reliable method for sex determination. Both the dimensions are more in male than in female.
Tooth morphology: In male, the distal accessory ridge in canines is more prominent than in female. In female, there is less number of cusps in mandibular first molar (distobuccal or distal). These features can be because of evolutionary reduction in the female lower jaw size.
Sex determination by DNA analysis: The study by Das and his associates stated that the sex determination could be obtained from the studying the X and Y-chromosomes upto four weeks of the death.