Introduction
Because physical anthropology is focused on the biological variation and evolution of humans, forensic anthropology utilizes the methods of description and analysis of human remains to establish the identity of an individual within a medico-legal context. “Medico-legal” context refers not only to potential criminal cases but also to missing persons cases, mass fatality incidents, humanitarian crises, and the repatriation of remains such as MIAs. Physical anthropologists, trained in human biology and anatomy (particularly skeletal), can assist in medico-legal investigations by determining sex and estimating race or ancestry, age, and stature during life;54-56 they can also contribute to facial reconstruction, DNA recovery and analysis, and estimating the postmortem interval (or time since death, TSD) as well as determining “evidence of foul play”.55
Forensic Archaeology and Anthropology
Forensic archaeology applies the methods of archaeology toward the search, discovery, documentation and mapping of human remains in a medico-legal context. Importantly, forensic archaeology is tasked with maintaining preservation of evidence and keeping the [potential crime] scene intact. Like prehistoric artifacts and fossils, forensic remains are often encountered by accident, often by construction activity or erosion, or, in the case of surface-level remains, by hikers and hunters.55, 57 Forensic archaeology is differentiated from the practice of forensic anthropology, which seeks to establish a biological profile (i.e., age, sex, race, and stature) of an unidentified individual.
Archaeological and anthropological practice intersect within the field of taphonomy, although taphonomic analysis may involve specialists from a number of scientific fields, including pathology, entomology, and botany. Taphonomy may be described as “the natural and the cultural events, processes, and agents that modify human remains from the time of death until the time of analysis.” 55, 58 “[D]ecomposing remains are part of a complex ecosystem,”59 and these changes include the internal processes of postmortem decomposition; perimortem trauma and postmortem physical damage; and activities of the surrounding environment (including insects and rodents, soil and weather conditions).59, 60 Taphonomic analysis can provide valuable evidence regarding manner of and time since death.
Anthropological analysis assists in the identification of unknown human remains by establishing a biological profile from which family members, witnesses or the larger public may be able to recognize and identify the individual, or providing a specific (positive) identification of an individual by matching dentofacial remains to dental records, evidence of antemortem injuries or surgeries to medical records, or recovering a DNA sample and matching the results to a known person. The dentition is particularly valuable in forensic identification in that record-keeping of patient history and treatment can provide matching evidence to enable positive identification (see Forensic Dentistry section below).
Determining sex: Skeletal elements, particularly the pelvis, skull and long bones, can lend valuable evidence for determining sex (not gender) based on human sexual dimorphism (anatomical variation in shape and size based on biological sex). Morphological and metric differences between adult males and females can estimate sex with an accuracy of between 90% and 98%.61 The pelvis is the most diagnostically valuable; the higher, narrower shape of the male pelvis visually contrasts with the lower, wider pelvis with flared ilia and wide pelvic inlet of females. The skull of males is typically “larger and more robust” than females (although the mandible, with its high degree of plasticity, is unreliable as an indicator of sex).61 Metric analysis of long bones, including the humerus, radius, ulna and clavicle, can estimate sex with an accuracy of up to 97%.61
Estimating age at death: Age at death can be estimated from a number of postcranial skeletal elements. The dentition of a subadult is the most reliable indicator of age (see below), but adults age can be estimated using a combination of techniques to provide an age range if the dentition is unavailable. The stage of epiphyseal union of long bones is useful in estimating age of persons under around 28 years of age, although nutritional status, population and sex may affect timing of epiphyseal fusion.37, 62, 63 The pelvis is almost as informative for estimating the age of an adult as it is for determining sex. Degenerative changes in the auricular surface and the pubic symphysis throughout adulthood are among the most reliable indicators of age in the adult skeleton.37, 64, 65 Other methods of estimating general age ranges for adults include the sternal end of the ribs,37, 56 and cranial suture closure.37, 63
Assessing race or ancestry: Gross examination of a human skull, free of soft tissue, can provide classification into the three major human populations (or “races”); the shape and angle of the eye orbits, shape of the nasal cavity, the extent of prognathism, and the relative width and length of the forehead and the braincase generally correspond to race.66, 67 The curvature of the human femur has been shown to reliably differentiate race.66, 67
Estimating Stature in life: The femur is also important in estimating the standing height of an individual in life. Simple formulae can be applied to femur length, as well as other long bones, for an estimation of stature, although these vary according to sex and ancestry.66, 68, 69
The most accurate method of providing such forensic identification is a combination of methods and application of statistical analyses, which are provided by software such as FORDISC,67, 70 which uses standard measurements of bones to estimate the sex and ancestry of adults, or CRANID, which estimates ancestry using discriminant analysis from measurements of a skull.67, 71
Forensic Dentistry or Odontology
Teeth are integral to forensic anthropology just as they are to academic anthropology; in addition to being the most durable part of the human skeleton, the teeth are highly genetically influenced, and specific developmental characteristics (such as spacing, winging) and dental treatment add to their importance in the positive identification of an individual’s remains. “Dental identification of a deceased person is a primary function of forensic odontology,”72 and forensic dentistry or odontology applies anthropological techniques to human remains identification using the dentition and related orofacial structures. While it is the responsibility of the forensic odontologist to analyze and describe the unidentified remains, the forensic odontologist relies on the practicing dentist to provide accurate and comprehensive dental records as evidence for a presumptive identification or rule-out tentative matches.73,74
Even without access to dental records, a general description of as-yet-unidentified remains may still be possible from the dentition. Forensic odontologists can estimate sex, age and race or ancestry and provide a general description of the unidentified person during life.
The first step in identifying remains is determining whether they are human or non-human. A number of bones of mammals such as bears and pigs can be confused with human bones, particularly the phalanges. Human teeth are easily distinguished from other animals including living apes.75 Humans have small, relatively obtuse canines and lack the canine-incisor diastema characteristic of apes. Human premolars and molars exhibit distinctly low, rounded cusps representative of omnivory as opposed to the high crests of herbivores and sharp, conical cusps of carnivores.76 As with parts of the appendicular skeleton, bears and pigs share some similarities in molar form with humans, although bear and pig molars are distinctly larger.63, 76
Estimating age from the dentition.
Subadult age is easily estimated based on the regular development and eruption sequence of primary and secondary teeth, to the time of the eruption of the third molars. Eruption sequence charts such as Schour and Massler’s seminal 1941 chart in JADA and, more recently, the London Atlas of tooth development and eruption are commonly used by both academic and forensic anthropologists.34, 36
By the time the adult dentition is completely developed, however, age estimation becomes much less reliable and it is more appropriate to classify age into broad intervals (e.g., ‘younger than 45’ or ‘greater than 50’). Methods of dental age assessment are covered in the ADA Technical Report 1077, Human Age Assessment by Dental Analysis, which describes radiographic, microscopic, and gross visual examination of tooth structures following development of the adult dentition. The technical report designates root translucency, secondary dentin deposition, periodontal attachment, cementum apposition, attrition and root resorption as criteria that can be utilized in the estimation of age of adult teeth.77ADA Technical Report 1077 was adopted by the American Board of Forensic Odontology as Standards and Guidelines for Dental Age Assessment, and accepted into the Registry of the Organization of Scientific Area Committees for Forensic Science in November, 2021 (see the ADA News story).
Determining sex from the adult dentition.
Human deciduous teeth and permanent canines exhibit sexual dimorphism of approximately 7%, although affected by ancestry which exhibits a similar dimorphism between Black and White Americans.63, 78 This difference in size between male and female teeth leads to a 75-80% accuracy in determining sex based on dentition.63 The pulp and dentin of teeth also provide a reservoir of DNA which enables sex to be determined from even fragmentary remains.79
Assessing ancestry or race from the dentition.
As discussed in the Anthropological analyses of teeth section, above, a number of metric and non-metric features can help assess geographic ancestry, although analysis of combinations of features and statistical probabilities are necessary for accurate results: no single dental feature can determine the population or “race” of an individual, but rather “complexes” of features help distinguish certain populations from others.75, 78, 80Shovel-shaped incisors are more common in Asian, especially Native American, populations, and the expression of accessory cusps, particularly Carabelli’s cusp, varies among populations; these traits are the most traditionally utilized in forensic identification.63, 66, 67, 78, 80, 81Generally, European-Americans tend to exhibit such nonmetric dimorphism in the anterior dentition, while African-Americans exhibit nonmetric variation more frequently in the posterior dentition.75 African populations typically display larger molars, while European-American dentitions are smaller and more crowded.63, 66 In addition, DNA retrieved from dental material can be analyzed for general indicators of ancestry or physical features including eye, hair, and skin color.82, 83
Other aspects of forensic dentistry: perimortem trauma and bitemark analysis
Evaluation of perimortem trauma may be carried out by a forensic anthropologist, but this task usually takes place from a licensed forensic pathologist, county coroner or medical examiner (although any of these may also be a forensic anthropologist). Forensic odontology has traditionally been involved in bitemark analysis, which, rather than identify a potential victim, instead may provide identifiable information of a perpetrator who may have left an imprint of the anterior dentition which might be matched to dental records. Although a number of studies have corroborated the accuracy of basing a positive identification on the uniqueness of the shape of the anterior dentition,84, 85 its legal and scientific value has been brought under scrutiny in recent decades.86-88
Responsibilities of the Practicing Dentist
Making a successful positive identification involves not only the work of law enforcement and forensic anthropologists but also extensive and detailed record-keeping by the practicing dentist. Several ADA policies (see ADA policies relating to dental anthropology, below), standards, and specifications (see below) encourage dentists, dental societies, and others to assist forensic investigations as permitted by applicable law and to follow procedures and standards designed to facilitate the positive identification of human remains.89
ADA Technical Report No. 1088 provides guidance for practicing dentists and others on methodologies and best practices for obtaining and reconciling forensic dental data for positive identification based on comparative dental analysis. ANSI/ADA Specification No. 1058 standardizes requirements for the documentation of dental information to help forensic odontologists make a positive match between a set or description of remains and dental records. As stipulated in ADA/ANSI 1058, the Antemortem Forensic Dental Data Set consists of six components: the Familial Data Set, Dental History, Tooth Data, Mouth Data, Visual Image, and Radiographic Image data sets.89
The ADA Center for Professional Success provides additional guidance on assisting a forensic investigation in The Dentist’s Role in Forensic Identification, which states:
A dentist who gets a request to provide dental records in a forensic investigation should cooperate with authorities…who present the dentist with a valid, properly served warrant, court order, subpoena or administrative order. State law, and possibly the HIPAA privacy regulations, determine the circ*mstances under which records may be release in the absence of a valid warrant or court order. Dentists may wish to consult with their private attorney in dealing with these situations.
Additional resources from the ADA for the practicing dentist wishing to be prepared for a forensic investigation include AADA SCDI White Paper 1100-2021: Codes for Orthodontic/Craniofacial/Forensic Photographic Views, and Copying and/or Transferring Records from Guidelines for Practice Success.
