الاسنان الصف الثاني

The Tooth


The tooth is an amazing sensory organ. The outside of the tooth, the enamel, is the hardest tissue in the human body. The enamel surrounds another layer of the tooth called the dentin. The tooth pulp lies in the middle of the tooth. The pulp contains blood vessels, nerve fibers and other connective tissue. Although the pulp has several functions, including the formation of dentin, the sensory function of teeth is quite interesting.
The nerve fibers inside teeth are exquisitely sensitive to stimulation when they can be activated. If you have ever had a cracked tooth or had a cavity in a tooth, you know that the message sent to the brain by the teeth is PAIN!!!. (The existence of a nonpainful sensory function of teeth is being debated in the current scientific literature). However, in undamaged teeth, the sensory fibers in teeth appear to be "quiet".
You may be thinking..."Wait a minute. If I touch my teeth, I feel the touch and it doesn't hurt. So the teeth must send nonpainful signals." It is true, of course, that if you touch your teeth you feel the touch. However, the sensation you feel is NOT the result of activating nerve fibers INSIDE the tooth. Rather, touching the tooth activates nerve fibers in the periodontal ligament (the ligament that surrounds the tooth) that are very sensitive to slight displacement of the tooth.
However, if the tooth is damaged by decay or trauma, the nerve fibers inside the tooth may respond to external stimuli and when they are, you are sure to feel pain.
Just for the record, children usually have 20 baby teeth (also called milk teeth). Adults have 32 permanent teeth. The 32 teeth in adults include the 3rd molars, also called the wisdom teeth. In some people the wisdom teeth do not come in at all.

Did you know?

These facts from Wynbrandt, J., The Excruciating History of Dentistry, New York: St. Martin's Press, 1998. The ancient Babylonians believed that demons and worms caused toothaches. Hippocrates recommended that teeth be cleaned with a ball of wool moistened with honey. Galen (129-201 A.D.), a famous Roman anatomist, advised people with toothaches to rub their gums with the brains of a hare. American patriot Paul Revere was also a dentist. The toothbrush appeared in Europe (possibly first in France) in the late middle ages. A toothpick factory can manufacture about 20 million toothpicks in one day. The giant anteater has NO teeth. (Source: Naples, V.L., Morphology, evolution and function of feeding in the giant anteater Myrmecophaga fridactyla, J. Zoology, 249:19-41, 1999).