Typically, the upper wisdom teeth have three roots, and the lower ones have two. The wisdom teeth, also called third molars, are the farthest back on each side of the mouth. A few people have more than four wisdom teeth, and some do not develop any.
If wisdom teeth develop, they are usually fully formed by age 14. However, most do not start to break through the gums until a person is at least 17. Sometimes there is not enough room for wisdom teeth to erupt. In these cases, the teeth emerge only partially or even remain stuck in the jaw, or impacted. Because of such problems, some people have their wisdom teeth extracted.