A primary tooth falls out because it is being pushed out of the way by the permanent tooth that is behind it. Slowly, the permanent teeth grow in and take the place of the primary teeth. By about age 12 or 13, most kids have lost all of their baby teeth and have a full set of permanent teeth.
There are 32 permanent teeth in all — 12 more than the original set of baby teeth. Most people have four teeth (called wisdom teeth) grow in at the back of the mouth when they're between 17 and 25 years old. These complete the adult set of 32 teeth.
Every tooth has the same two parts: a root, or roots, to anchor it in the jawbone, and a crown, the part that can be seen in the mouth. There are four different materials in a tooth. The "enamel" is hard shiny and covers the crown. The "cementum" is a bone like material that covers the root. The "dentine" is an ivory-like material that forms the body of the tooth. The "dental pulp" is in a hollow space called "the pulp chamber" inside the tooth. The dental pulp is made up of tissue that contains nerves, arteries, and veins. These enter the tooth through an opening at or near the root end. Lack of calcium or Vitamin D in the diet will result in poor enamel, which will encourage early decay. The process of dental decay is also aggravated by the collection of sugary or starchy foods around the teeth, especially during the night. As they decompose in the mouth, these foods produce acids that will act on the calcium of the teeth and make them soluble, causing the teeth to soften, and thus allow bacteria to attack them. Why do teeth sometimes grow "crooked"? The reason varies with each person, but scientists say that the way the jaws have developed in modern man can cause this problem. It seems that man's jaws today do not always provide enough room for his teeth. So they appear in a crooked position or become shifted during the period of growth. If this happens to a tooth in the lower jaw, the opposing tooth in the upper jaw also becomes crooked in position. This sometimes causes teeth to stick out, or pushes the lips out, or makes the chin recede, and spoils the appearance of the mouth.
