Though your teeth are very hard and glassy looking on the surface, they are much softer and chalkier inside; this glassy coating covers only the crown, or free part, of the tooth, which you can see. It leaves the softer inside part of the tooth bare just at the edge of the gums, and particularly between the roots of the teeth, where little scraps of food lodge and decay. When the acids that are formed by the decaying food have eaten away a good deal of the inside of the tooth, the hard, shiny surface is left just like a thin shell; and one day you happen to bite down upon a piece of bone in your food, or try to crack a nut with your teeth, and “crack” goes this brittle shell of your hollow tooth.
Right in the middle of each tooth is a tiny hollow, or cavity, filled with a soft, living pulp containing one or two very sensitive nerves; and when the decay has eaten into the tooth far enough to reach this nerve pulp, it makes it ache, and then you have toothache.
The one and only thing that is necessary in order to avoid all this decay and breaking away of your teeth, and throbbing toothache, is to keep the surface of your teeth, and particularly the sides where they are next one another, clean and smooth and unbroken. And all that is needed to keep your teeth perfectly clean and smooth is to use your toothbrush thoroughly after every meal and at bedtime; and then, if there are any little scraps of food between the teeth that have not been brushed away, to pick them out gently with a quill toothpick, or take a piece of silk or linen thread, push it up between the teeth, and gently saw backward and forward until you have cleaned out the space between the roots. You should take at least three to five minutes after every meal and before you go to bed at night to brush your teeth; and you should brush not only your teeth, but the whole surface of your gums close up to where they join the lips.
It is almost as important to keep your gums pink and hard and healthy as it is to keep your teeth clean; and the same thorough brushing will do both. If the gums are perfectly healthy, they will come well down over the roots of the teeth, and keep them safely covered right down to where the glassy outer coating begins, and so leave no gap where the acids of decay can attack the teeth. Be sure to brush your teeth, not merely straight backward and forward, but up and down and round and round as well, both to clean out thoroughly all the grooves and openings between them and to brush the gums well down over the teeth.
It may seem strange, but one of the best ways to keep your teeth from growing crooked and irregular is to keep your nose clear and healthy, so that you can breathe through it freely at all times, both day and night. Crooked jaws and irregular teeth are more often caused by mouth breathing than by any other one thing.
You can see why it is best to be careful not to get grit or dirt or bits of bone in your food, and not to crack nuts or hard candy with your teeth. If you do, you may crack or scratch the delicate glassy coating of your teeth. But, on the other hand, it is a good thing to give the teeth plenty to do, and particularly to eat the crusts of bread, and some of the tougher parts of meat, and parched corn or other grains, and to eat celery, apples, and other foods that take a great deal of chewing. The teeth are like everything else in the body—they need plenty of vigorous work in order to keep them healthy.
Be very careful, though, to keep out of your mouth anything that might possibly crack or scratch the glassy coating, such as pins, pennies, pieces of wire, or slate pencils. It is best not even to try to bite off threads or pieces of string. There is, of course, another reason for not putting pencils and pennies and such things into your mouth: they may have dirt, or germs, on them and infect you with disease or at least upset your digestion.
II. THE LAND OF NOD
Now you are all ready for bed; and the white pillow and the nice, clean sheets and the warm blankets look very good to you, and you are ready to go to the “Land of Nod.”
You need not be afraid of the cold at night. Open your bedroom windows. Have plenty of light-weight, warm covers; then the cold breezes won’t hurt you, but will make you strong. Just think how many hours you are in bed,—nearly half of your life,—and you need fresh, moving air all the time. Be sure to open your windows from the top as well as from the bottom. You know why: your breath is warm so that it floats and rises like smoke; and if you open the window only at the bottom, this bad air, which rises to the top of the room, can’t get out. It is best to have windows on two sides of a bedroom, so that the air can be kept moving through it all night long. If you don’t breathe fresh air while you sleep, you will feel dull and stupid in the morning and perhaps have a headache.