In this edition of ‘Know Your Pathology’, we shall examine the subject of calculus, also known as calcified plaque. This consists of micro-organisms, which accumulate in the mouth, embedded in a matrix partly composed of the organisms themselves and partly derived from proteins in the saliva (Roberts and Manchester, 2005: 71). It accumulates faster when there is a high protein and/or carbohydrate diet favouring an alkaline oral environment (Roberts and Manchester, 2005: 71).
Where crystallites of mineral are deposited in the plaque, the plaque can be mineralised and form calculus (Roberts and Manchester, 2005: 71-71). Two types are commonly seen:
- Supragingival calculus (above the gum) is more common and is usually thicker and grey or brown in colour;
- Subgingival calculus (below the gum) is often seen on exposed tooth roots and is harder and green or black in colour.
Calculus varies widely in mineralisation, but subgingival calculus is more heavily mineralised (46-83% by colume) than supergingival (16-80% by volume). The minerals include apatite, whitlockite, octacalcium phosphate and brushite, all of which have been found in archaeological specimens (Hillson, 1996: 257). Brushite is prominent during the earlier part of calculus deposition, whilst mature supergingival calculus has more apatite and brushite, and subgingival calculus has abundant whitlockite (Hillson, 1996: 257).
Beneath a Scanning Electron Microscope, it is possible to see that calculus is more heavily mineralised than dentine or cement, but less so than enamel, and that it presents an irregular appearance with layerings, voids and clefts (Hillson, 1996: 257). Outlines of bacteria are presented as voids with mineralised shells – the filamentous forms as 2um diameter tubules, and shorter rods or cocci as globular outlines – and similar outlines have been demonstrated in calculus from English medieval human remains (Dobney and Brothwell, 1986).
Dental reports from some archaeological human populations indicate that calculus was common in all periods (Roberts and Manchester, 2005: 72).
Dobney, K and Brothwell, D. 1986. Dental calculus: its relevance to ancient diet and oral ecology, pp 55-82. In Cuwys, E and Foley, R.A. Teeth and Anthropology. BAR International Series 291. British Archaeological Reports: Oxford
Hillson, S. 1996. Dental Anthropology. Cambridge University Press: Cambridge.
Roberts, C. and Manchester, K. 2005. The Archaeology of Disease. 3rd Edition. Stroud: Alan Sutton Publishing Ltd.
NB: For those looking for past editions of ‘Know Your Pathology’, and so that I can keep track of which topics I’ve covered and which I’ve not, there is now an index.