Matthew Law

Above: SEM images of dental calculus, by Matthew Law - click image to zoom, click arrows to scroll between pictures (requires Microsoft Silverlight)

Dental calculus is a condition often observed both on archaeological and modern teeth. Calculus occurs when the plaque that forms on the surface of the mouth mineralises. Two forms are recognised: supragingival calculus, which forms above the gum line and can occur in quite large accretions; and subgingival calculus, which forms below the gum line and presents as a hard layer adherent around the tooth. Because dental calculus has a mineral composition, it survives in all but acid burial environments (Dobney and Brothwell 1986: 55). It is most commonly observed in individuals with a high protein/ low carbohydrate diet (Chamberlain 2006: 164).

In life, plaque forms on the tooth surface and the margin of the gingiva (Miles and Grigson 1990: 522) after eating when saliva that contains food substance remains attached to the surfaces of the teeth and gingiva. The normal movement of the tongue and lips may detach this layer, however if fermentable carbohydrates are present in the food substance, then the microbial flora will include organisms or enzymes able to convert the carbohydrate into sticky high-end polymers, which will make the plaque layer much harder to dislodge (Miles and Grigson 1990: 522). In these circumstances, a particular microbial flora dominated by gram-negative and filamentous organisms arises. The products of this flora are often irritating to the marginal gingiva, causing chronic gingivitis (Miles and Grigson 1990: 522).

Dobney and Brothwell (1986: 55) investigated the organic components of calculus in an attempt to locate food particles which have become incorporated into the matrix (ibid.: 58), using a mix of human, cattle and sheep samples. With radiography, they reported distinctive zoning of the calculus (ibid.: 66), and, as well as phytoliths, they revealed microbes within the calculus under SEM (ibid: 77), and a wide range of diverse fragments under light microscopy, including cereal chaff epidermis and animal hair (ibid.: 69, 71). Hardy et al. (2009) examined dental calculus from skeletons from Turkey and the British Isles, to look for plant starch granules preserved in the calculus matrix, and found that there is great potential for reconstruting palaeodiet using starch from calculus.

References

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

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

Hardy, K., Blakeney, T., Copeland, C., Kirkham, J., Wrangham, R., and Collins, M. 2009: Starch Granules, Dental Calculus, and New Perspectives on Ancient Diet. Journal of Archaeological Science 36: 248-255

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