A tooth is a bit like a tree — only part of it is visible, and the roots
lie beneath the surface. The roots of your teeth extend into your gums
and beyond into the jaw bones. Your tooth has many layers. The outer
layer (enamel) is made of hard crystal. The next layer (dentin) is
softer. The pulp in the middle of the tooth contains nerves that conduct
sensations of hot, cold and pain. The pulp also contains blood vessels.
