Teeth
The adult human normally possesses 32 permanent teeth. The tooth has a central area called pulp, which contains blood vessels and nerves. Pulp is surrounded by dentin. The visible part of the tooth is covered with enamel which is the hardest substance in the human body. The enamel can be destroyed by wear or tooth decay; damaged enamel is not repaired by the body.
The tooth is surrounded by gums, which help hold the tooth in place. Under the gum layer, and surrounding the tooth, is cementum. This layer provides nutrients to the tooth.
There are three types of teeth: incisors, canines and molars. Incisors are flat teeth located in the front of the mouth and used for cutting and tearing. Canines (in other mammals called tusks) are sharp and pointed. The molars are large square teeth found towards the back of the mouth. They are used for grinding.
Teeth first appear about six months after birth, and are called milk teeth. They are not permanent, and are lost gradually from about 6 to 18 years of age. The permanent teeth erupt during this same period of time.
References
Crafts, R.C. 1985. A Textbook of Human Anatomy. John Wiley and Sons, Inc. New York. 906 pp.
Lockhart, R.D., G.F. Hamilton, et.al. 1974. Anatomy of The Human Body. Faber and Faber Limited. London. 697 pp.
Van Amerongen, C. The Way Things Work; Book Of The Body. New York: Simon and Schuster, 1979.
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