by Matthew Law

Teeth are first part of the body anything an individual eats, drinks, or smokes comes into contact with. The enamel of teeth is also the densest and hardest of all skeletal tissues, and occasionally can be all that survives of the organism archaeologically (Rackham 1994: 20). Teeth are also often very easy to identify even in the absence of the body that originally contained them (Hillson 1979: 147). Many vertebrates - including most cartilaginous and bony fish, reptiles other than turtles, amphibians, and most mammals - have teeth, although vertebrates that do not have teeth include birds, turtles, baleen whales, some bony fish, and some ant-eating mammals (Reitz and Wing 1999: 47).

Teeth are subject to a number of variations and pathological conditions, which can reveal much about the life history of the person or animal being studied, and about their genetic inheritance. Examples of these include enamel hypoplasias, which can reveal that the individual suffered ill health or poor diet in childhood (Hillson et al. 1999: 102). Cavities in the tooth, known as caries, are the result of a diet high in carbohydrates (Hillson 1996: 278), while mineralised plaque on the teeth, called calculus, may contain remains of the individual's diet  (Dobney and Brothwell 1986: 69, 71).

Teeth gradually wear down through life, and a number of methods of aging the individual have been devised based on the pattern and extent of such wear, both for humans (Brothwell 1981: 72), and for other mammalian species such as sheep (Payne 1973: 293). Smaller wear patterns called microwear may be visible under scanning electron microscope, and can be caused by the enamel being scratched while eating, or by the use of teeth as tools (Danielson and Reinhard 1998: 298).

Age at death

Teeth and jaws are the most useful elements of the skeleton for telling us the age at death of the individual, as teeth undergo a series of eruption, wear, and loss that can be used to determine developmental age (Rackham 1994: 10). It is important to realise that 'developmental age' is not necessarily the same thing as actual age, as different individuals within a single population will doubtless reach particular developmental stages at different ages, and separate populations of the same species may differ by greater amounts, especially as a result of genetic or nutritional variation (Rackham 1994: 12). Castration may have an effect on tooth wear in sheep - in a study of Shetland sheep, teeth were noticed to wear faster in rams than in whethers, although castration did not appear to affect tooth eruption (Davis 2000: 378).

The percentage of the adult postcanine occlusal area (that is, the parts of the teeth that meet when the individual's mouth is shut behind the canine teeth) that is present at weaning is known as the dental endowment at weaning, and the percentage of total postcanine primary (deciduous) and secondary (permanent) teeth that have erupted at different developmental ages is known as dental precocity (Godfrey et al. 2001: 192).

Human mandible, showing advanced tooth wear. Photo by Matthew Law

Season of death

In mammals, cementum, which is laid down at the base of the tooth, is deposited with an annual pattern of growth, with the greatest increment in the summer, and a lesser increment - which appears as a narrow, dark, line - in the winter (Rackham 1994: 13). By counting the dark lines, the number of years the animal survived after the eruption of the tooth can be determined (Rackham 1994: 13), although it should be noted that these lines may not always be observable (Rackham 1994: 13)

Anatomy of teeth

Four types of tooth attachment to the jaw are known among vertebrates. Most mammals and crocodilians have a type of attachment called thecodont, where the teeth have roots that fit into sockets, or alveoli, in the upper and lower jaw. Most other reptiles and amphibians have teeth that are anchored on a bony shelf, a type of attachment called pleurodont. Most bony fish have a type of attachment called acrodont, where teeth are attached to bones by pedestals at their base, while cartilaginous fish, such as sharks and rays have multiple rows of teeth that are attached to cartilage by fibres known as Sharpey's fibres (Reitz and Wing 1999: 44).

Most vertebrates have two sets of teeth: milk teeth (known as deciduous teeth), and permanent teeth. This is known as diphyodont. Toothed whales, however, only have one set of teeth, and so are monophydont. Animals that replace their teeth constantly through their life, such as reptiles and fish, are polyphydont (Reitz and Wing 1999: 45).

In mammals, there are four types of teeth: incisors, canines, premolars, and molars. The generalised dentition for the left arcade of eutherian (placental) mammals is

(Hillson 2005: 12), meaning that the upper and lower jaw would each contain three incisors, one canine, four premolars, and four molars.

For Homo, the dentition follows the form

(Hillson 2005: 44). The prefix d refers to deciduous teeth (see above).

The crown of the tooth is usually the part visible in the mouth during life, and is covered in enamel. The root is the part of the tooth that is held in the alveoli, and is coated in a bone-like tissue called cementum, or simply cement. Underlying these layers is a hard material called dentine (which is the source of ivory). Protected by the dentine is the pulp chamber (Hillson 2005: 8)

There is a great deal of natural variety among teeth of different individuals of the same species. These morphological variations in teeth are divided into two groups: metrical and non-metrical variations (Hillson 1996: 9). Metrical variations are those that can be measured directly (such as variations in the size of teeth), while non-metrical variations are those which are usually scored visually, perhaps in terms of presence or absence, or according to a scale of degree of development, although some studies have attempted to measure them as well (Hillson 1996: 69). Examples of non-metrical variation in human teeth include a variation in the size and number of cusps on the molars (Hillson 1996: 88); a variation in the form of grooves on the lower molars (Hillson 1996: 93-96); extension of the enamel beneath the cervical crown margin, or even a separate nodule of dentine capped with enamel, known as an enamel pearl, found on the root (Brothwell 1981: 116; Hillson 1996: 97, 98). Double-rooted canines are often noted in early British remains (Brothwell 1981: 117).

Diseases of teeth

Calculus:

Dental calculus is plaque that has mineralised and adheres to the teeth (Lieverse 1999: 219). A number of methods exist for the recording dental calculus in the laboratory (McCreanor 1999: 41).

Part of a sheep mandible. The black accretion on the teeth is dental calculus. Photo by Matthew Law

Caries:

Caries is a condition in which acids which cause demineralisation of the enamel and dentine are created by the fermentation of  carbohydrates by bacteria (Chamberlain 2006: 162), resulting in localised damage. The study of dental caries in humans has proven especially helpful in studying the transition from a hunter-gatherer lifestyle to agriculturalism (Hillson 2001: 250). A thorough method for recording dental caries in the laboratory is described for human remains by Hillson (2001: 249-289).

Deliberate modification of teeth

Cases of deliberate tooth modification, usually filing or chipping of the teeth, in humans are known from the Americas, Africa, Australia, Egypt, Europe, and south-east Asia (Brothwell 1981: 116). Tooth evulsion (the deliberate removal of teeth) is not common in European archaeological populations of humans, however the deliberate removal of incisors, was practiced in Italy during the Neolithic, and appears to have survived in Etruria into the Classical period (Becker 2002: 239). It most of the Etruscan cases, the upper central incisors, which are believed to have been deliberately removed, have been replaced using gold pontics, or bridges (Becker 2002: 241).

References

Becker, M.J., 2002: Etruscan female tooth evulsion: gold dental appliances as ornaments, in Baker, P.A., and Carr, G. (eds) Practitioners, Practices and Patients: New Approaches to Medical Archaeology and Anthropology (Oxford: Oxbow) 239-259

Brothwell, D.R., 1981. Digging Up Bones. Third Edition. Ithaca: Cornell University Press

Chamberlain, A., 2006. Demography in Archaeology. Cambridge: Cambridge Manuals in Archaeology

Danielson, D.R., and Reinhard, K.J., 1998: Human Dental Microwear Caused by Calcium Oxalate Phytoliths in Prehistoric Diet of the Lower Pecos Region, Texas. American Journal of Physical Anthropology 107: 297-304

Davis, S.J.M, 2000: The Effect of Castration and Age on the Shetland Sheep Skeleton and a Metric Comparison Between Bones of Males, Females and Castrates. Journal of Archaeological Science 27, 373-390

Dobney, K., and Brothwell, D., 1986: Dental Calculus: Its Relevance to Ancient Diet and Oral Ecology, in Cruwys, E., and Foley, R.A. (Eds), Teeth and Anthropology. Oxford: BAR International Series. 55-81

Evans, J. G., 1978: An Introduction to Environmental Archaeology (London: Elek)

Godfrey, L.R., Samonds, K.E., Jungers, W.L., and Sutherland, M.R., 2001: Teeth, Brains and Primate Life Histories, American Journal of Physical Anthropology 114, 192-214

Hillson, S., 1996: Dental Anthropology. Cambridge: Cambridge University Press

Hillson, S., 2001: Recording Dental Caries in Archaeological Human Remains. International Journal of Osteoarchaeology 11: 249-289

Hillson, S., 2005. Teeth. Second Edition. Cambridge: Cambridge Manuals in Archaeology

Hillson, S., and Bond, S., 1997: Relationship of Enamel Hypoplasia to the Pattern of Tooth Crown Growth: a Discussion, American Journal of Physical Anthropology 104, 89-103

Hillson, S., Grigson, C., and Bond, S., 1998: Dental Defects of Congenital Syphilis, American Journal of Physical Anthropology 107, 25-40

Hillson, S., Antoine, D., and Dean, C., 1999: A Detailed Developmental Study of the Defects of Dental Enamel in a Group of Post-Medieval Children from London. In: J T Mayhall and T Heikkinen (eds.) Dental Morphology 1998: 102-111. Oulu University Press. (http://herkules.oulu.fi/isbn951425497X/)

Hillson, S.W., 1979: Diet and Dental Disease, World Archaeology Volume II Number 2: 147-161

Lieverse, A.R., 1999: Diet and the Aetiology of Dental Calculus. International Journal of Osteoarchaeology 9, 219-232

McCreanor, M., 1999: Measuring supragingival calculus in humans: the Surface Occupation Method, in Anderson, S. (ed): Current and Recent Research in Osteoarchaeology 2, Proceedings of the fourth, fifth and sixth meetings of the Osteoarchaeological Research Group. (Oxford: Oxbow) 41-43

Payne, S., 1973: Kill-Off Patterns in Sheep and Goats: The Mandibles from Aşvan Kale. Anatolian Studies XXIII: 281-303

Rackham, J., 1994: Animal Bones (London: British Museum Press)

Reitz, E.J., and Wing, E.S., 1999, Zooarchaeology. First Edition. Cambridge: Cambridge University Press 

See also Calculus, Mesiodistal Diameter

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