Another way by which little pieces are chipped off the teeth is by biting hard things. Sometimes we see boys and girls cracking nuts with their teeth; again we see them trying to bite wires in two. They put their teeth to many uses for which teeth were never made. They do not realize, while they are abusing their teeth in this way, that they are probably chipping the enamel, which is the hard, shiny covering of the tooth, and are destroying the one protection that their teeth have against decay. [Sidenote: Why teeth decay] When a little piece is chipped off a tooth, an opening is made through the enamel. Through this opening germs may lodge in the inner part of the tooth, which is soft. When this happens, a little black speck appears on the tooth, and after a while the tooth begins to ache. If you have a toothache, you go to a dentist, and he probably finds that germs have caused the tooth to decay until there is a hole extending into the very center of it. Teeth grow very close together, but there is always a little space between them. Whenever you eat anything, particles of the food get into these spaces and if allowed to remain there, soon decompose. These decomposing particles of food between the teeth will gradually soften even the enamel, and in this way little openings are made for germs to get into the teeth. [Sidenote: How to care for the teeth] Never pick the teeth. You cannot make them clean by picking them. Every morning and night brush your teeth with a stiff toothbrush and a little tooth powder. Brush them both crosswise and up and down, to get out everything from between them. Do not think you have done your duty if you brush only your front teeth, the ones that show. Brush the back teeth just as thoroughly as you do the front teeth. Very few people will see your back teeth, but these decay just as fast as your front teeth, if they are not kept clean. [Illustration: FIG. 24. A sanitary wash-basin with a separate bowl for washing the teeth.] [Sidenote: How often one should go to the dentist] Twice each year you should have a dentist examine your teeth, to see if there are any little spots where decay has started. If you have kept your teeth perfectly clean all the time, and have not chipped off little pieces, there will be none of these decayed spots. But it is a safe plan to have the teeth looked over at least twice a year, for you may have broken a tooth without knowing it, and by the time a decayed spot is large enough to cause pain, or has made a hole that you can feel with your tongue, it has advanced much farther than it should have been permitted to do. =Questions.= 1. Why should you chew your food thoroughly? 2. Why is it necessary to have baby teeth? 3. How are teeth easily broken? 4. Why do teeth decay? 5. What must you avoid in order to protect your teeth? 6. How should your teeth be brushed? 7. Why should you have your teeth examined twice each year by a dentist?