We have learned that chewing is not merely a process of cutting our food into such lumps as we can swallow without hurting ourselves; but that the food must be ground up fine and thoroughly mixed with the saliva, that the saliva may reach every particle of starch. If we do not have good teeth, we cannot grind our food as fine as it ought to be ground, and, as a result, a great deal of the starch will not be reached by the saliva.
Nature starts every child with a full set of good, strong, clean teeth. These teeth, which we call first, or milk, teeth, are not very large, but they are perfect in every respect and last until the second, or permanent, teeth come in. That is, they will last so long if they are taken care of. If they are not taken care of, they will decay just as the later teeth will decay, and they must be cared for in the same way.
Why we have baby or milk teeth
Boys and girls sometimes wonder why they have a set of teeth that come out before they can have the teeth that must last them the rest of their lives. This is simply because there is not room enough in a child's mouth for the big, permanent teeth. We must have teeth while our jaws are growing, so we have first a set of little teeth. Then just as soon as our jaws get large enough for the big teeth, the little teeth come out and the big ones come in.
Teeth are about the hardest substance in the body. If we take care of our second teeth, they should last as long as we live. The only reason they do not last is because we do not take care of them. If a person would keep his teeth clean all the time, he would rarely be obliged to have a single permanent tooth pulled.
Why teeth break easily
Teeth are so hard that they are brittle, that is, they break easily. Glass is brittle, and you can chip off a piece of glass with a pin by sticking the pin into a crack in the glass. In just the same way you can chip off a piece of a tooth by sticking a pin between two teeth. That is what often happens when people pick their teeth with pins, or with any other hard substance. A metal toothpick is just as bad as a pin.
Fig. 23. Teeth were not intended for nutcrackers.