What is dental calculus?

Calculus is a deposit of calcium phosphate salts on the surface of teeth. Sometimes it is also called tartar but this term is less commonly used these days.

There is no fixed composition of dental calculus because the type and amount of calcium phosphate salt which precipitates onto the tooth surface is affected by a variety of local factors such as

I could go on, in fact almost any local condition you care to name will have at least some effect on the type of mineral which deposits. It is, therefore, difficult, or even impossible, to be definitive about calculus composition beyond the fact that it comprises a mixture of calcium phosphate minerals such as:

Calculus Formation

Calculus forms wherever a solution of calcium and phosphate becomes unstable. This can happen in various parts of the body such as the kidney (kidney stones), the gall bladder (gall stones), the bladder (bladder stones) and salivary glands and ducts (sialoliths). When it happens in the mouth the deposit is called dental calculus and sometimes tartar.

Calculus forms most readily within dental plaque in fact it is often referred to as mineralised plaque. The surface of calculus is rough and provides an excellent site for further plaque growth which in turn may become mineralised. Calculus then often has a layered structure.

One way in which calcium phosphate may become destabilsed is by elements of dental plaque acting as seeding agents in much the same way as collagen provides epitactic sites to act as the seed for mineralisation in bone, dentine and cementum formation. Among the many different species of bacteria in dental plaque there is some evidence that the most likely seed is Leptotrichia buccalis.

This only works, of course, if the plaque is bathed in a solution supersaturated with respect to the variety of calcium phosphate minerals depositing at the site. For more on this see the tutorial on salivary calcium phosphate.

In addition to the presence of a suitable epitactic site such as that found in dental plaque, calculus often needs an additional impetus to form. This is provided by the extra-alkaline conditions of ductal saliva.

The pH of saliva is dictated by its bicarbonate concentration. Read more about this.

At high flow rates saliva contains large amounts of bicarbonate which starts to reduce the moment the saliva enters the mouth according to this reaction.

Obviously the scope for reduction is small because there are few protons available. Nevertheless, ductal saliva and saliva in the immediate area adjacent to the salivary gland ductal openings are at a slightly higher pH which means that the calcium phosphate is less stable here.

If the effect of the presence of plaque with its seeding properties are taken together with the higher pH in the areas adjacent to the salivary ducts it explains why most calculus is found on teeth next to the openings of the parotid and submandibular ducts. This doesn't mean that plaque will not form elsewhere, it will.

Clinical Implications

Calculus forming at the gingival margin whether it is sub- or supra-gingival will cause inflammation of the gingiva (gingivitis) which may progress to periodontal disease. An example of calculus induced gingival inflammation is shown opposite.

The inflammation is the result of physical irritation of the gingiva as well as the presence of bacterial toxic by-products in the calculus. Remember, most calculus is mineralised plaque which comprises very many different bacterial species. Furthermore, fresh plaque is readily deposited on the calculus surface.

Quite apart from aesthetic reasons, Inflammation and its sequelae are the reason why calculus must be removed.

Dental calculus is widespread in all age-groups from teenagers onwards throughout the world. However, the levels of calculus are dependent on the population studied and are affected by a number of factors (see table opposite).

Supragingival calculus is minor and is restricted to surfaces adjacent to the salivary ducts in populations which practice good oral hygiene and have access to professional dental care. In this case calculus has a small or neglible effect on oral health. Also in these populations any subgingival calculus is coincident with loss of periodontal attachment but does not seem to be the cause of it. Attachment loss is caused by dental plaque.

In populations which do not practice good oral hygiene and which do not have access to professional dental care, supragingival calculus commonly occurs throughout the dentition and can be present in very large amounts. In these populations supragingival calculus is associated with gingival recession and subgingival calculus, which is also extensive, is directly correlated with enhanced loss of periodontal attachment although the exact relationship is not clear because it is impossible to seperate the different contributions of subgingival calculus and any associated plaque.

So it is not clear if the calculus is the cause of the periodontal inflammation or the result of it.

Removal of subgingival plaque and calculus is the main plank of periodontal therapy.

Inhibition of calculus formation

This has been the subject of much research since inhibition of calculus formation will reduce the need for professional prophylaxis.

Supragingival calculus formation can be effectively controlled by chemical mineralization inhibitors, applied in toothpastes or mouthrinses. These agents act to delay plaque mineralisation, keeping deposits in an amorphous non-hardened state to aid theirremoval with normal tooth brushing and flossing.

Current formulations in anticalculus dentifrices and mouthrinses utilise either zinc salts or 1% soluble pyrophosphate.

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