Saliva does more than patients imagine, and it can be measured

Saliva is perceived as an incidental fluid, whereas it is the principal defence system of the oral cavity, and its reduction produces consequences that appear all at once.

There are at least five functions. It dilutes and clears debris, buffers acids, supplies calcium and phosphate for remineralisation, contains antimicrobial components, and lubricates the mucosa.

Buffering capacity is what bears most on caries. After a sugar intake the pH falls, and how quickly it rises depends on salivary bicarbonates.

A patient with reduced buffering capacity stays in the acidic range far longer on the same diet, which explains why two people with similar habits carry different risks.

Flow is measured under two conditions. At rest, collecting saliva over several minutes without stimulation; stimulated, by having the patient chew an inert material.

Reference figures indicate around 0.3 millilitres per minute at rest and 1 millilitre per minute or more under stimulation. Values below 0.1 at rest and 0.7 stimulated define hyposalivation.

Collection is carried out away from meals and with no smoking or toothbrushing for at least an hour, otherwise the figure is comparable neither with the reference nor with a later measurement.

The distinction between the two values is clinically useful. Low resting flow with normal stimulated flow indicates functioning but underactive glands, a different situation from a reduction in both.

In the first case one can act on stimulation with sugar-free gum, on hydration and on a review of medication; in the second glandular damage is more likely and expectations must be calibrated.

Medication is the commonest cause of reduced flow, and the list is long: antihypertensives, antidepressants, antihistamines, diuretics, anxiolytics. Patients rarely connect a dry mouth with the therapy they take.

A medication history is therefore part of the examination, and in patients on multiple drugs it is worth checking at every recall because therapies change.

A documented reduction in flow changes the plan: high-concentration fluoride, closer recalls, saliva substitutes, and attention to root caries, which is the form appearing first.

In summary: buffering capacity explains differences in risk on the same diet, flow is measured at rest and stimulated against known references, the distinction between the two guides treatment, medication is the commonest cause, and reduced flow justifies a different protocol.