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Published in Dental Historian 2015; 60 (2): 51-62
Unlocking the past: the role of dental analysis in archaeology
Roger Forshaw
Abstract
What can the study of ancient teeth tell us about the life style and dietary habits of our
ancestors? Dental palaeopathology is particularly important as it can provide direct
evidence of the type of diet an individual consumed during life. An analysis of the angle of
tooth wear evident on the crown of the tooth can help to distinguish between early hunter-
gatherers and later agriculturists, whilst microwear features on the occlusal surface can help
to discern subtle dietary shifts. The distributions of stable isotopes in food webs make it
possible to use them to reconstruct ancient diets as well as tracing the geographic origins
and migrations of peoples. Plant microfossils have been isolated from calculus which can be
identified using light microscopy. Teeth are particularly useful in ancient DNA studies due to
the excellent preservation of biomaterials within the enamel shell of the tooth.
Key Words
Dental palaeopathology, caries, calculus, enamel hypoplasia, tooth wear, stable isotopes,
ancient DNA
Introduction
Teeth are not only the most highly mineralised tissue in the body but they are also the hardest
and most chemically stable, usually surviving long after their supporting structures have
deteriorated. In contrast to bone teeth interact directly with the environment during
mastication and as a result can provide information about the diet and health of a deceased
individual during life. Whilst bones may well suffer post-decomposition over time, teeth are
usually sufficiently well-preserved to allow visual and scientific analysis. Analytical
techniques that are now available to unlock information from teeth, relating to the life-style
of our ancestors, are wide-ranging and continually expanding. Dental palaeopathology,
however, is fundamental to any study of ancient teeth as it provides direct evidence of the
type of diet that an individual consumed during life.
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Dental Palaeopathology
Caries
Dental caries can be an important indicator of dietary variations between different historical
populations. The disease can be traced far back in geological time and to all parts of the
world, but early humans were less affected by caries than modern populations. This can be
illustrated by considering the ancient Egyptian population. In the Neolithic Period when the
ancient Egyptians where predominately hunter-gathers, they consumed a diet rich in protein
with few simple carbohydrates and as a result had little caries experience. After 4,000 BC
society developed into a sedentary agricultural lifestyle with bread being the stable food, but
as the variety of bread consumed was composed primarily of complex non-fermentable
carbohydrates, caries was still fairly negligible. However, with the arrival of the Greeks into
Egypt in the 4th century BC, foodstuffs such as fine white bread, honey and dates became
more freely available and caries incidence rose significantly.1
A dramatic difference in caries experience within a population, separated by only a short
space of time, is illustrated by considering the example of the Inuit who inhabit Canada,
Greenland and Alaska. Up to the early part of the 20th century the Inuit consumed primarily a
high protein and fat diet consisting of seal, caribou, fish and walrus, a diet that resulted in less
than one cavity per individual being recorded. However, with increasing contact with the
North American and Canadian cultures the diet increasingly became one of purchased foods
from trading posts, foodstuffs that included high levels of refined carbohydrates. This rapid
change of diet which occurred within a single generation resulted in figures of between eight
and fifteen cavities per individual being noted.2,3
Periapical Cavities
Severe tooth wear, gross caries and trauma can precipitate pulpal necrosis which results in the
release of bacteria and their toxic products into the periapical tissues. Such an incursion
would elicit an inflammatory response, the level of which would depend on the balance
between the immunity of the host and the virulence of the infection. Low-grade infection is
likely to result in a chronic inflammation response, the most common reaction being a
periapical granuloma which would create a void in the surrounding bone. Over time this may
develop into an apical periodontal cyst. Such periapical cavities are useful dietary indicators
and it is not uncommon to observe multiple periapical cavities in a single specimen (Figures
1a and 1b).
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1a 1b
Figs. 1a and b: Right and left lateral views demonstrating multiple
periapical cavities above the roots of the maxillary teeth.
Unprovenanced skull from ancient Nubia.
(Courtesy of the Duckworth Collection, the University of Cambridge)
However, if the pulp were to be infected by a virulent strain of bacteria then an acute abscess
would develop. Such an abscess rapidly invades the alveolar intertrabecular spaces and
vascular channels but does not form a bony cavity because of insufficient time for
osteoclastic resorption to occur. Pus tracks through bone taking the path of least resistance
until it reaches an outer surface where it would discharge, except in rare cases where the
rapid extension of the infection to adjacent bone marrow spaces could produce
osteomyelitis.4
As mentioned above a factor in the progression of these infections is host resistance or its
impairment by systemic disease and this might have been a significant factor in antiquity.
Many of our ancestors may well have been debilitated by chronic diseases such as
tuberculosis or various parasitic infections, diseases which today are treatable. In such
compromised individuals or where the virulence of the infecting agent is high then serious
complications may ensue. Bacteraemia could result which if untreated, as it would have been
in antiquity, could progress to generalised septicaemia and be fatal.5
In the historical record, the potential for an abscess to spread causing severe sepsis and death
has long been recognised.6 In the early 1600’s the London Bills of Mortality frequently listed
‘teeth’ as the fifth or sixth leading cause of death.7 DeWitte and Bekvalac8 examined skeletal
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remains dating from AD 1350-1538 excavated from a medieval London cemetery and their
findings indicated that oral pathologies were associated with an elevated risk of mortality.
Even by the turn of the 20th century dental infections were still associated with a significant
risk of death. A study by Thomas9 determined a death rate of between 10 and 40 per cent of
those admitted to hospital with dental infections.
Periodontal Disease
Whilst the diagnosis of periodontal disease in the dental surgery is usually straightforward,
detecting periodontal disease in skeletal material, without the presence of the soft tissues, can
be problematic. An increase in the distance between the cemento-enamel junction and the
alveolar crest, inaccurately used as an indicator of periodontal disease in the past, has often
been shown to be due to continuous eruption as a result of tooth wear. Identification of
periodontal disease in skeletal material needs to be based on characteristics such as altered
shape of the alveolar margin and the presence of macroscopic porosity on the alveolar bone
caused by resorption of the cortical plate which reveals the underlying porous cancellous
structure.10,11
Using criteria such as these studies indicate that in ancient populations periodontal disease
involving horizontal loss of alveolar crestal bone loss was not common and if it did exist was
usually of minor severity in comparison to modern populations.12,13,14 Clarke and Carey15
suggested that this may be due to more effective host defence systems functioning within the
gingival crevice and gingivae compared to modern populations where these systems may be
compromised by persistent or combined environmental factors such as smoking, diet and
unhealthy life-style options.
Ante-mortem tooth loss (AMTL)
The loss of teeth prior to an individual’s death is recognisable by progressive resorption of
the alveolar bone. Differential diagnosis of the aetiology of AMTL may yield important
information regarding patterns of behaviour in ancient peoples. Excessive tooth wear, caries
periodontal disease, traumatic injury and dental ablation for aesthetic or ritual reasons are
significant precipitating factors. Also, generalised conditions such as nutritional deficiency
disorders may contribute to the frequency of AMTL.16
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Calculus
Calculus, being highly mineralised, survives well in the archaeological context and an
analysis of calculus can be useful in furthering our understanding of ancient lifestyles.
Calculus formation is facilitated by an alkaline oral environment and diets high in protein
increase this alkalinity thus contributing to the formation of calculus. However, many other
factors such as individual variation, cultural practices, the degree of mineral content in the
drinking water, presence of silicon and bacterial involvement in the mineralisation process
are all factors which would affect the deposition of calculus.17 The presence of large
quantities of calculus on ancient teeth is by itself not necessarily an indicator of specific
dietary patterns but does supply evidence that may assist in determining such patterns.
During the process of calculus formation food particles and plant microfossils are trapped
within the calcium phosphate matrix, an environment in which they are well-protected. A
sample of this calculus can be chemically treated to release these microfossils. These are then
identifiable by means of light microscopy and are able to provide a direct record of particular
plants consumed during life.18
As to be described below, stable isotope analysis is an important technique in the
construction of past subsistence practices. However, it is a destructive procedure as rare
archaeological specimens have to be physically sampled which inevitably would result in
damage to the specimen. Scott and Poulson19 describe a new technique in which calculus is
analysed for carbon and nitrogen isotope concentrations. The results of this study compare
favourably with those obtained from other biomaterials such as bone, collagen and teeth. As
calculus is a secondary biomaterial and not an integral part of the skeleton, this technique has
the potential to overcome curatorial concerns regarding sample preservation.
Enamel Hypoplasia
Enamel hypoplasia is a quantitative defect of enamel commonly occurring as discrete pitting
or horizontal furrows on the tooth surface. The hypoplasia is due to a disruption in the
secretion of enamel during crown development, resulting in incomplete or defective
formation of the enamel crown matrix. Some hypoplasias are related to inherited conditions,
but generally these are rare with the majority of defects being caused by environmental
stressors such as disease and poor nutrition.20 The distance of the hypoplastic disturbance
from the cemento-enamel junction is an indicator of the age at which the disruption occurred.
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Because enamel is non-vital tissue such defects are never erased from the tooth and enamel
hypoplastic lesions provide a ‘memory’ of biological disruptions during childhood.21
The prevalence of enamel hypoplasia in ancient teeth has been used by Starling and Stock22
to study the transition from a nomadic foraging lifestyle to a sedentary agricultural regime.
The dentitions of five populations who inhabited the Nile valley in Egypt, spanning the
period 13,000-1,500 BC, were studied. The results of the research indicated that the
frequency of hypoplasias was significantly higher in a proto-agriculturist population dating c.
5,000-4,000 BC than amongst early hunter-gatherers, and also higher than among later
populations. This suggests that the period surrounding the emergence of early agriculture in
the Nile valley was associated with high stress and poor health. However, the health of the
agriculturists improved substantially following increased urbanisation and trade that
accompanied the formation of the Egyptian state. This development resulted in more
guaranteed food supplies, improved health and a reduction in the incidence of hypoplasias.
Tooth Wear
All dentitions display evidence of some loss of tooth tissue due to physiological wear but the
tooth wear frequently observed in ancient populations is far more extensive than is evident in
modern society today and is often considered as pathological in nature.23,24 This excessive
wear was mainly due to the hard fibrous foods consumed by our ancestors, foodstuffs
frequently contaminated by inorganic abrasive particles. These contaminants would have
arrived from a number of sources such as the use of flint-tooth sickle harvesting tools, the
ingress of particles from the soil which had not been sieved out and mineral fragments from
soft sandstone implements used to grind the grain.25
Excessive tooth wear, therefore, is an indication of the type of diet consumed by an
individual, but the pattern of this wear can also provide additional dietary information.
Historically, the teeth of both the early hunter-gatherers and the later agriculturists are
characterised by rapid pronounced tooth wear, but it is the angle of crown wear rather than
the absolute degree of wear that can help to distinguish between these groups. This variation
is related to the major differences in subsistence and food preparation. Hunter-gatherers
develop flatter molar wear due to the mastication of tough fibrous food where the teeth do not
often make contact during mastication. However, with the prepared food of the agriculturist
which comprises ground grain and food cooked in water, the teeth are in contact for longer
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periods. Mastication in this case involves grinding and sliding of the teeth against each other,
a process which results in oblique tooth wear.26,27
Fig. 2: Photo-simulation of microwear showing pits and scratches.
Late Archaic Period individual, Indiana, USA.
(Arrows indicate pits. Courtesy of M. Zolnierz, University
of Arkansas and C. Schmidt, University of Indianapolis)
Fig. 3: Photo-simulation of microwear showing scratches.
Early Late Archaic Period individual, Indiana, USA.
(Courtesy of M. Zolnierz, University of Arkansas
and C. Schmidt, University of Indianapolis)
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Not only does the angle of the tooth wear provide information but studies into microwear
features observable on the tooth surface can also yield additional dietary evidence. Dental
microwear is the name given to the pits and scratches that form on the surface of enamel
during mastication (Figures 3 and 4). They differ according to diet and so examining and
recognising these traits can be useful in establishing past dietary patterns. Pits are caused
when hard abrasive particles are driven or compressed into the enamel surface of the tooth.
This process results in cracks in the crystalline structure of the enamel and as a consequence
minute fragments fracture away from the tooth surface. Scratches occur when particles are
dragged between opposing enamel surfaces as the jaw moves through the chewing cycle.28
The technique of dental microwear analysis involves a statistical evaluation of the wear facets
of molar teeth, mainly the cusp tips which are used primarily for crushing and the patterns on
the cuspal slopes which are used for shearing. This procedure originally involved using an
electron microscope to scan replicas of the wear facets and then identifying the individual
features.29 However, such a technique is limited by observer error and a high cost in time and
money. A more recent approach is that of dental microwear texture analysis which utilises a
white light confocal microscope to examine the tooth surface. This method permits the
collection of true 3D surface data which is then analysed spatially in a geometric technique
known as scale-sensitive fractal analysis.30
The results of the technique indicate that individuals eating harder foods requiring greater
masticatory forces tend to have a greater number of and larger pits, whilst those eating softer
foods tend to have mainly scratches. However, these traits are not mutually exclusive and
occlusal surfaces usually show evidence of both pits and scratches. Dietary patterns are
determined by which microwear features are dominant in a particular population.31
Stable Isotopes
Stable isotope analysis is a technique that is useful in the reconstruction of ancient diets, in
tracing the geographic origins and migrations of peoples and also in studying human weaning
history. Carbon, nitrogen, oxygen and strontium isotopes are those commonly studied whilst
collagen extracted from bone or dentine is the structural protein analysed. Teeth are
particularly useful because of the excellent preservation of biogenic elements in the tooth
structure and their resistance to diagenesis.
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Stable isotopes of carbon are the most widely used palaeodietary tracer and the technique
utilises the carbon content of carbon dioxide in the atmosphere which occurs primarily in the
two isotopically stable forms of 13C and 12C. Isotopes of carbon are universal in the structure
of plants and animals but the level of 13C and 12C varies between different groups of animals
and plants. Carbon diffuses into the pores of plants as carbon dioxide during photosynthesis
with differing groups of plants obtaining carbon from the carbon dioxide in different ways.
The C3 photosynthetic pathway, in which the first product of photosynthesis is a 3-carbon
compound, is used by most temperate zone vegetation. Tropical and sub-tropical grasses,
which include the domestic crops sorghum, millets, maize and sugar-cane, employ what is
known as the C4 pathway, in which carbon is fixed initially into a 4-carbon compound.32
Different plant groups are, therefore, incorporating differing amounts of carbon isotopes into
their plant tissue and the two plant groups are quite distinctive and do not overlap. When
these plants are consumed the carbon isotopes they contain are incorporated into the
hydroxyapatite of bones and teeth in differing amounts. The main component of the diet is
then able to be identified by quantifying the relative amount of each isotope within the
hydroxyapatite, using the technique of mass spectrometry.33
This technique has been used to demonstrate the increasing importance at that time of rice
over millet in a late Neolithic site in Shandong, China.34 Dupras and Tocheri35 have been able
to reconstruct infant weaning histories using stable isotope analysis of the dentition, whilst
stable isotope ratios of carbon and oxygen have helped in understanding Neolithic
subsistence patterns in northern Borneo.36
Strontium and oxygen isotope ratios in hydroxyapatite have been used to study the
geographical origins and movements of ancient peoples. Strontium isotope ratios vary in
different types of rock and soil and as a result there are differences in isotopic ratios in plants
and animals living in regions with different geology.
DNA
DNA is the genetic material of living cells and the information it contains controls the
structure, development and metabolism of the body. The recovery of this genetic material
from skeletal tissues has become a central research tool in many scientific fields. There are a
number of anthropological questions that can potentially be addressed by DNA analysis such
10
as the determination of sex when conventional identification methods are impossible as well
as the origin, relationships and movements of human populations.37 Merriwether et al.38
obtained DNA from teeth and bones in order to study ancient migrations to the New World.
Haaka et al.39 examining remains from 4,600-year-old graves near Eulau, Germany were able
to detect child-parent relationships. Papagrigorakis et al.40 investigated a mass burial pit, at
Kerameikos near Athens dating back to the time of the Plague of Athens (c. 430 BC).
Through DNA examination of pulp obtained from teeth excavated at this site these
researchers were able to detect Salmonella enterica serovar Typhi, therefore establishing that
typhoid fever was the probable cause of the plague, a scenario that had only been speculated
upon previously.
Although there are smaller amounts of cellular DNA in teeth compared to bone, teeth are
commonly used as the outer acellular enamel protects the dentine from environmental
deterioration.41 Many methods used by molecular researchers such as sectioning, crushing or
grinding destroy the morphological structure of teeth and therefore cause curatorial concerns
with both anthropologists and museum curators. However, Alakoç and Aka42 describe a
method for obtaining DNA from an ancient molar tooth in which an entrance cavity is
prepared in the occlusal surface of the tooth which is then extended into the pulp chamber.
Pulpal and dentinal tissue is removed by the use of K-files and the tooth restored with a
composite filling. A sample is therefore obtained for DNA analysis but the physical structure
of the tooth is re-established and a rare archaeological specimen is protected from being
destroyed.
Multiple Techniques
Increasingly, teeth are being analysed by multiple scientific techniques. Lillie and Richards43
used both dental palaeopathological evidence and stable isotope analysis to help understand
diet in the transition from the Mesolithic to the Neolithic periods in the Ukraine. Hogue and
Melsheimer44 utilised both stable isotope analysis and dental microwear analysis to observe
dietary changes over time in east-central Mississippi. Cagnon et al.45 analysed oral health
indicators and microfossils found in calculus to track changes in the habit of coca chewing in
South America.
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Conclusion
Whereas studies based upon caries, alveolar resorption, rates of tooth wear and other skeletal
features can provide a general view of diet, the application of more advanced scientific
techniques can be more specific in their findings. These techniques form an essential part of
archaeological and anthropological investigations since a comprehensive visual and scientific
analysis of ancient teeth can provide information that might otherwise not be retrievable from
the archaeological record and which may help with a better understanding of earlier
populations.
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3 R.L. Costa, ‘Incidence of caries and abscesses in archaeological Eskimo skeletal samples from Point Hope and
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12
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40 M.J. Papagrigorakis, C. Yapijakis, P.N. Synodinos, E. Baziotopoulou-Valavanic, ‘DNA examination of
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44 S.H. Hogue, R. Melscheimer, ‘Integrating dental microwear and isotopic analysis to understand dietary
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