Teeth are white and hard tissues in our body that we donate to the tooth fairy.
First off, teeth are lined up in two separate lines. The upper line is called the maxilla and the lower one is called the mandible. The development of teeth starts during the pregnancy period. In the last three months of an embryo's stay in its mother, the teeth become calcified – using the minerals which the mother consumes through the umbilical cord.
The eruption of teeth usually starts from 6 months after birth. The first set – which are called the milk teeth / baby teeth / deciduous teeth or primary teeth – and consist of 20 teeth (10 in the maxilla and 10 in the mandible), all rise till the age of 2 years. From then on these teeth start to fall and give their spots to more mature biters called Secondary teeth or Permanent teeth. Permanent teeth are 28 (14 in the maxilla and 14 in the mandible).
The period in which the mouth consists of both Primary and Secondary teeth, is called the mixed stage. The permanent teeth are usually completely erupted by the age of 12. This just leaves 4 more teeth called the wisdom teeth. These four usually erupt by the age of 18, but in some people in later years and even never in others.
The lining of the Primary teeth just has one less pre-molar, one less molar and no wisdom tooth on every quarter of the mouth:
1) The external structures: the Crust which is the white thing of a tooth we see above the gum. Whatever is under the gum is called the Root.
2) The internal structures: the pulp is the part of the tooth which the blood vessels and neurons/ nerves run through. Dentine is the stuff which surrounds the pulp. These two are in the Root section. The enamel is the white part we see when we open our mouth. So most of the crust is taken up by enamel and only a tiny fraction is covered by dentine. Cementum is another tissue which has the role of sticking the teeth to the jaw bone.
Enamel is the hardest tissue in the human body though it is brittle. But the Dentine is less mineralized and relatively softer and less brittle, so needed for support.