Let's see why the man didn't immediately cut the final set of teeth; why appear first dairy in order to fall out and be replaced by permanent teeth.
Do you know what the kit includes 20 primary teeth teeth, and the permanent set - 32? And you know why?
The thing is that, when the infant becomes necessary in the teeth (that is, when it starts to move to solid food - it is somewhere in the 6-9 months), the jaw of a child is still very small. During the growth of the child growing up and his jaw. You might have noticed that by 6 years between milk teeth become quite large? This is because the jaw grow, and teeth - no.
Meanwhile, the permanent teeth begin to form under the milk teeth (which have not yet erupted!) already shortly after birth.
6-7 years to these teeth begin to erupt. This process is accompanied by resorption of the roots of the milk teeth. From this milk teeth loosened. When shortened root can no longer hold a baby tooth in the hole, it falls. Gradually, one by one, the milk teeth fall out to make room constant. Change of milk teeth permanent usually ends up to 12-13 years.
One of the important functions of primary teeth is that they "indicate" bicuspid place for cutting. When a baby tooth falls out ahead of time (for example, when it is necessary to remove), permanent tooth loses landmark" and can grow crooked.
In the set of permanent teeth, as mentioned above, there is a set that is not in the set of milk teeth. This is 2 pairs of premolars in each jaw. They are located between the canines and posterior (indigenous) teeth.
20 + (4*2) = 28. Where else 4 teeth 32? And this so-called wisdom teeth. They erupt last approximately between 17 and 21 years. By the way, if the jaw is small, and the space for wisdom teeth to it, these teeth may not erupt, and man lives with a set of 28 permanent teeth.
It is interesting
Permanent teeth erupt in the same sequence as dairy: first the first pair of incisors on the lower jaw, then a pair of incisors of the upper jaw; followed by another pair of cutters. Behind the front teeth at the age of from 9.5 to 12 years receive a premolars, and then the fangs (from 9 to 12 years) and, finally, the second molars (11 to 13 years).