Wisdom tooth is the last of the molars in the mouth. It is the last tooth to come into the mouth at the age of 18 to 22 years. This tooth may be missing in some people, when they have only 28 teeth in the jaw. Sometimes, due to lack of space in the jaws, the wisdom tooth may not come out fully. It may at times come in a different direction than the normal. At such times we call the tooth an impacted tooth- locked in the bone. Such impacted teeth can get infected and cause pain. This condition is more common in the lower jaw of the mouth.