Saliva is not just moisture; it neutralises acid, repairs enamel and limits bacteria. What happens when it falls, and why decay then develops so fast.
Saliva is a fluid we never think about while it is healthy and which disrupts everything in the mouth once it falls. Some patients see a dry mouth only as a discomfort, yet dryness is a genuine risk factor that multiplies the rate of decay.
How much saliva is produced daily
A healthy adult secretes about a litre and a half of saliva a day. Most comes from three pairs of major glands, while hundreds of minor glands scattered through the mouth produce a small, continuous flow.
The flow is not constant. It peaks during chewing and almost stops during sleep. The mouth is therefore left unprotected overnight, which is why cleaning before bed carries particular weight.
Neutralising acid
After sugar is taken the pH inside the plaque falls quickly and enamel begins to dissolve. Bicarbonate and phosphate buffers in saliva neutralise the acid, and the environment returns to a safe range in about twenty to thirty minutes.
Knowing that period matters, because every snack starts a fresh acid attack. Grazing through the day gives saliva no chance to recover. What determines decay risk is the frequency of these attacks more than the amount of sugar.
Repairing enamel
Saliva is saturated with calcium and phosphate. The minerals drawn out of enamel during an acid attack are carried back once the environment neutralises. This is remineralisation, and it is why early decay can be halted.
When fluoride joins the process, the crystal formed is more resistant than the original. Saliva and fluoride therefore work together; without one, the effect of the other is markedly reduced.
Limiting bacteria and healing wounds
Saliva contains defence molecules such as lysozyme, lactoferrin and immunoglobulins. These suppress bacterial numbers and limit fungal overgrowth. The continuous flow also mechanically removes bacteria that are only beginning to adhere.
Part of the reason wounds in the mouth heal faster than elsewhere in the body is saliva; the growth factors it contains speed tissue repair.
Taste, chewing and speech
Taste molecules can only reach the taste buds once dissolved in liquid. When the mouth dries, flavours fade and patients often complain of poor appetite. Turning a mouthful into something swallowable likewise depends on saliva.
Comfortable movement of the tongue and lips in speech also needs a moist surface. In occupations involving long periods of speaking, a dry mouth directly affects voice quality.
What happens when saliva falls
When flow falls, all of these functions weaken at once. The result is a picture familiar in the surgery: many cavities in a short time, particularly on the root surfaces near the gum and along the edges of the front teeth.
- Medicines: for blood pressure, antidepressants, antihistamines, diuretics
- Radiotherapy to the head and neck
- Sjögren's syndrome and some autoimmune conditions
- Uncontrolled diabetes and dehydration
- Mouth breathing and snoring
Ways to increase the flow
Chewing is the strongest stimulus. Sugar-free gum, especially one containing xylitol, chewed for ten minutes after a meal markedly increases flow and neutralises acid quickly. Drinking water relieves dryness temporarily but does not increase secretion.
Caffeine and alcohol deepen dryness by increasing fluid loss through urine. Smoking both reduces flow and irritates the mucosa. In a patient with a persistently dry mouth, reviewing these three is the first step.
Managing a patient with a dry mouth
The cause is investigated first; where a medicine is responsible, an alternative can be considered in discussion with the patient's own doctor. On the dental side, protection is intensified: high-fluoride toothpaste, a fluoride rinse and more frequent check-ups.
A few dietary adjustments are also needed. Dry, crumbly and sticky foods are harder to swallow for these patients and remain longer on the tooth surface. Keeping water with meals, softening food and confining sugary snacks to mealtimes make a clear difference.
Artificial saliva products and moisturising gels give relief particularly at night. Alcohol-based rinses are avoided. A six-month recall is usually too long for these patients; every three months is more appropriate.
