A wisdom tooth or 3rd molar has its name because it comes in when one reaches approximately age eighteen, which is the beginning of adulthood.
Human beings have evolved rapidly throughout the history and so have teeth and jaws.
When ancient people fed on mostly vegetables, it is said they had as many as forty-four teeth. With the discovery of fire and the following mastery of the knowledge and skills necessary to tenderize food, people began to eat softer food. As a result, the size of jaws became smaller. Moreover modern people have fewer teeth and normally there are thirty-two teeth including both upper and lower wisdom teeth.
The wisdom tooth is the last tooth that comes in and there isn't much space left for it to grow properly. For this reason these days only a few people have completely grown wisdom teeth. They are sometimes impacted in a bone or partially erupted, which causes painful swelling. Especially inflammation on the gums that cover the back of the wisdom teeth is called pericoronitis.
This inflammation prone condition and its last position in the set of teeth make it hard to be reached for brushing and often leads to the tooth decay.
There are a few people who don't have any problems with their wisdom teeth as long as their wisdom teeth grow normally along with other molars and they can easily brush them.
However, in most cases, dentists will examine the X-rays to see your oral conditions and decide for you whether those teeth should be extracted


< picture: An X-ray that shows a impacted wisdom tooth which gets stuck when it grows by the next tooth.>