The term "wisdom teeth" comes from the fact that they appear to 17-18 years

The term "wisdom teeth" comes from the fact that they appear to 17-18 years, the age of wisdom. But this is indicative because these teeth may appear to that age there but also to 20, 30 40 and even 80 years!
These teeth are behind the molars at the end of the jaws.
They are supernumerary teeth
They have a bad reputation because when they are talking about it are terribly wrong.
These are those below which poses the greatest problem because they are located in the corner of the jaw and have little room to grow.
They are tilted forward and they are growing pressure on adjacent teeth.
Moreover their roots are practically in contact with the dental nerve.
If the upper teeth pose fewer problems because the shape of the upper jaw is different and the wisdom teeth will have more space.
These teeth we make them because it happens to come not from their embryo sac when they appear, as he arrives for the other teeth, and in this case there is an infection and extremely painful péricoronarite .

Most people have 4 (one in two) but the other half have a number ranging from 1 to 6, or even no!
It may even have two that grow in place of one;;;;

Why opt for their extraction?
Because it does not cause nearly as trouble!
They are located at the mouth are making their brushing assez difficile. In addition when they grow they tend to rely on adjacent teeth and so they promote the emergence of dental caries in place of contact not accessible to brushing!
They can also be extracted as a preventive measure to adolescence, if radio shows that the seeds have a position which may impede the adjacent molars.