Although the hurry and bustle of modern life is apt to make people forget it, mastication is a most important part of the digestive process. During early life the stomach and intestines may be able to digest imperfectly-masticated food, but as years advance they cease to do so, and imperfect mastication becomes a fruitful source of dyspepsia.

If the teeth are entirely or almost entirely gone, the person may chew with his gums, but if they are only partially gone it frequently happens that those which remain oppose one another only sufficiently to prevent the gums from closing, while they do not help mastication.

The decay of teeth is chiefly due to the dentine being attacked by the acid products of the decomposition of food in the mouth. This decomposition is to a great extent due to bacteria, and antiseptics are therefore useful in preventing decay.

By cleaning the teeth with a soft brush at night before going to bed, particles of food sticking between them may be removed, and thus its decomposition and consequent injurious action on the teeth may be avoided. Chalk is employed as a basis of most dentifrices, as its mechanical action is sufficient to clean the teeth without injuring their polish, and at the same time it neutralises any acid which may be present. Charcoal has also a useful mechanical action greater than that of chalk, but it is more liable to scratch the enamel.

The antiseptics which are usually employed to cleanse the teeth are borax, quinine, and carbolic acid. Dilute solutions of permanganate of potassium are also very useful, but have a very disagreeable taste. Where the gums are soft and spongy and are apt to leave the fang of the tooth more or less exposed, vegetable astringents, such as areca nut, catechu, kino, and rhatany are useful. Mineral acids when given medicinally cause an unpleasant feeling of the teeth being on edge, and are also injurious to the teeth; they are therefore usually sucked up by means of a glass tube or quill, instead of being simply swallowed. When used as gargles for the throat, their injurious action on the teeth may be to a considerable extent prevented by previously rubbing the teeth with oil, butter, or lard, and washing out the mouth or brushing the teeth with a weak solution of alkaline bicarbonate or soap. Soluble preparations of iron, especially persalts, are apt to stain the teeth, and they are therefore also given by means of a tube; alum appears also to have a very injurious action on the teeth; alum gargles should therefore not be employed for a length of time together, and the same precautions should be used as with acid gargles.

When the gums have receded somewhat from the crown of the teeth, pain or a soreness is not unfrequently felt in the teeth, although no definite caries is present. This soreness appears to be due to the irritant action of acid secretions in the mouth upon the exposed fang, and it may be often to a great extent removed by washing the mouth out with a weak solution of bicarbonate of sodium, or rubbing finely-powdered chalk or magnesia along the gums. When toothache occurs in consequence of caries, it may sometimes also be relieved by holding some brandy in the mouth, or by placing a small pledget of cotton-wool dipped in tincture or liquid extract of opium with a little bicarbonate of sodium in the cavity of the tooth. A pledget of cotton-wool dipped in creasote or oil of cloves is often used for a similar purpose, and one of the most effectual remedies is to dip a small pledget of cotton-wool in pure carbolic acid liquefied by heat, and place it in the cavity of the tooth, taking care to cover it well with clean cotton-wool so as to prevent the carbolic acid coming in contact with the tongue or cheeks. Chlorate of potassium often lessens toothache if due to inflammation of a large open carious cavity. Phosphate of calcium frequently relieves toothache occurring during pregnancy or lactation and is sometimes useful also in toothache unconnected with either of these conditions.