This section is from the book "Health", by W. H. Coefield.
The food that we eat requires to be prepared in various ways before it can become part of the structures of which our body is composed. To this end, there is a complex apparatus contained in our bodies, and there are certain liquids provided in connection with this apparatus, and certain organs in which these liquids are made, and thereby the food that we take is reduced to a condition in which it can be assimilated to the structures of our own bodies. This apparatus we call the digestive apparatus; and this apparatus and its working I am now going to describe.
The digestive apparatus begins, as before mentioned, with the mouth. The mouth is a cavity, the walls of which are partly bony and partly muscular and fibrous; the upper part of it, the roof, is what we call the palate, the front part of which is bony, and the back part muscular and fibrous; there is then the hard palate and the soft palate; the side walls of the cavity of the mouth are the cheeks, which are for the most part muscular, and which are capable of being moved in various ways; and just inside the cheeks are the jaws. At the floor, we have a large organ, which we call the tongue, which is almost entirely muscular, composed of several layers of muscles, layers which run in different directions, so that the tongue is capable of a great variety of movements. At the front of the mouth we have the lips, forming a valve, and an opening to the external air; at the back of the mouth is an opening communicating with another cavity, called the pharynx.
These are the boundaries of the cavity of the mouth, and the beginning of the digestive apparatus.
In the first place, in this cavity we notice that the edges of the jaws are provided with a special set of instruments, the teeth-instruments for cutting, tearing, and grinding the food. These instruments are fixed into the jaw-bones, just as nails are fixed into a board.
The whole of the cavity of the mouth is lined, and the whole of the digestive apparatus is lined, by a membrane, which is continuous with the external skin of the body. You will remember I have mentioned in a previous Lecture that the membrane which lines the different cavities of the body communicating with the external air is called the mucous membrane, and so the mouth, and the rest of the digestive cavity, are lined with mucous membrane.
This mucous membrane around the edges of the jaws, into which the teeth are implanted, becomes harder and more firm than it is in other places, and goes by the name of the gums; it is continued right down into the holes in which the teeth are implanted, and over the parts of the teeth which are implanted in the jaws, and which we call the roots of the teeth, so that the teeth are not merely fixed in the jaws by their roots, but the holes, or sockets, in the jaws, and the roots of the teeth, are lined by a firm, tough membrane. This renders their position in the jaws more secure than it would otherwise be.
The teeth are of several kinds, but all have certain characters in common. In the first place, the part projecting above the gums is called the crown of the tooth; below this, at the attachment of the gum, is the neck of the tooth; then the teeth have processes below projecting into holes in the jaws-these processes are called roots, or fangs, and each tooth has one or more of these processes; besides this, every tooth has a cavity in its interior which is continued down right through the root or roots of the tooth, so that at the end of each root or roots there is a perforation leading into this cavity, and it is through those holes or perforations that the blood-vessels and nerves pass into the teeth. You will see from this that the teeth, just like the bones, form part of the living structure of the body, and change just like any other part of the body, only not at the same rate. The bulk of each tooth is made up of a substance, which is only found in teeth, which goes by the name of dentine, a substance harder than bone; for, whereas bone contains about one-third of organic matter and two-thirds of inorganic or mineral matter, dentine contains only a quarter of organic matter and three-quarters of mineral matter. Around the fangs of the teeth there is placed a small quantity of a substance called cement, almost exactly resembling bone; and upon the crown there is a substance which covers the whole of it above the gum, which is the hardest and most indestructible substance in the human body, and goes by the name of enamel; it consists almost entirely of inorganic or mineral matter.
Tou can now see from the structure of the teeth how very important it is that the crown of the tooth should not be broken,injured, dissolved,or decayed in anyway. The enamel on the crown of the tooth is extremely hard, and especially fitted for the purposes for which the teeth are used. It is not a very thick layer, and if broken by biting hard substances, or decayed by want of attention to the cleansing of that part of the tooth which is above the gum, then the dentine is exposed and it is quickly destroyed; for if the enamel, which is harder than that, is not sufficient for your purpose, the dentine cannot be. When the dentine begins to go it goes very fast indeed, and the teeth decay into the cavity in the interior of the tooth; that is how the nerve gets exposed, and we get those pains which are familiar to most of us. You can see, then, from the construction of the teeth what an important thing it is to take care of them. Now, these are the things which are common to all teeth. But teeth are of different kinds, and there are two sets of teeth; there is the first set of teeth, which we call the milk teeth; they are also called the temporary teeth, because they are teeth which we only retain for a small portion of our lives; and there is another set, which we call the second or permanent set of teeth.
As the teeth of the two jaws are sufficiently alike, and those on each side of each jaw are alike, I will describe the teeth on one side of one jaw.