The teeth being constantly moistened with saliva, have a tendency to become incrusted with the tartar or earthy matter which it contains in solution, and which is separated from it partly by the evaporation of the more fluid constituents in breathing, and partly by chemical decomposition. As this incrustation not only destroys the beauty of the teeth, but also promotes their decay, it becomes an object of care to remove it as soon as it is formed; and the most effectual mode of doing so is to brush the teeth regularly twice a day—especially in the morning, when the quantity is greatest—with a brush dipped in soft water, till every particle is removed. The addition of any soft impalpable powder will assist in the effect; but nothing capable of acting chemically on the teeth, or of injuring them by friction, ought ever to be resorted to. Washing the mouth after every meal is also a good preservative.[14]
When the teeth are not used for a time, and when digestion is impaired, the quantity of tartar which accumulates on them is very great. Hence they are always most incrusted in the morning, and in fevers and other affections where no food is taken, and the stomach is at the same time disordered. I have seen one instance in which a thick crust of tartar was removed by a dentist in the belief of its being a diseased tooth—the tooth itself on which it was formed being left in the jaw perfectly sound.
When the tartar is not duly removed, its presence injures the teeth, irritates the gums, and generally leads, sooner or later, to considerable suffering. The regular washing and brushing above mentioned ought, therefore, to be sedulously practised at every period of life, and taught as a duty to the young. When digestion is very vigorous, the health good, and the diet plain and containing a full proportion of vegetable matter, the deposition of tartar seems to be diminished, and the teeth to be naturally of a purer white. Many rustics and savages thus possess teeth which would be envied in a town.
When digestion is impaired, and acidity prevails in the stomach, the mucous secretions in the mouth also become altered in character, and by their incessant contact injure and even destroy the teeth. From this cause we often see the teeth in young people in a state of complete decay. They are in reality the subjects of chemical decomposition, and eaten away by the morbid secretions of the mouth; and hence, in such cases, we generally find the individual complaining of heat and soreness of the tongue, gums, and mouth, and occasionally of the teeth being “set on edge.”
Considered as living parts, the teeth require some additional care. In that capacity they are exceedingly apt to suffer from sudden changes of temperature. Being from their solidity rapid conductors of heat, their internal nerve speedily becomes affected by the alternations of temperature to which they are daily exposed, both in taking food and in the change from a warm to a cold atmosphere. It is a not uncommon practice, for example, to take a glass of cold wine or water immediately after finishing a plateful of very hot soup; and it is quite usual to take tea and coffee and every kind of meat as hot as they can possibly be swallowed—than which practices it would be difficult to imagine any thing more hurtful to the teeth.
For the same reason, in going out at night from a warm room to the coil air, it is desirable to protect the teeth from the influence of the sudden change, by breathing through two or three folds of a silk handkerchief, or through a woollen comforter. When the teeth and lower part of the face are left exposed in such circumstances, rheumatism and toothach not unfrequently ensue from the direct impression of the cold air upon parts rendered more susceptible by the preceding heat.
The great source of injury to the teeth, however, both in childhood and in mature age, is disordered digestion. If the health be good, and the stomach perform its functions with vigour, the teeth will resist much exposure without sustaining injury. But if these conditions fail, they will rarely continue long unscathed.
It is almost always from the latter cause that, in infancy, teething so often gives rise to serious constitutional disorder.
Something more, however, than the mere action of the teeth and jaws is required to prepare the morsel for being swallowed. If we take a bit of dry biscuit or mealy potato into the mouth, and attempt to masticate it, we encounter at first no small difficulty from the stiffness and resistance of the dry mass, and feel instinctively that it would be in vain to attempt to swallow it, until moistened either by continued mastication or by the admixture of fluid from without. In ordinary states of the system, accordingly, a fluid called saliva or spittle is copiously secreted and poured into the mouth for this very purpose; and the process by which its due admixture with the contents of the mouth is accomplished is called the insalivation of the food.