Matthew Law

Above: SEM images of dental calculus, by Matthew Law - click top left corner to zoom, drag image to explore(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).

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).

References

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

Miles, A.E.W., and Grigson, C., 1990: Colyer’s Variations and Diseases of the Teeth of Animals. Revised Edition. (Cambridge: Cambridge)

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