A wisdom tooth, in humans, is any of the usual four third molars.
Wisdom teeth usually appear between the ages of 16 and 25.
 Most adults have four wisdom teeth, but it is possible to have fewer (hypodontia), or more, in which case they are called supernumerary teeth. Wisdom teeth commonly affect other teeth as they develop, becoming impacted or "coming in sideways." They are often extracted when this occurs.
If the wisdom teeth are impacted, angulated or partially erupted wisdom teeth can cause following:
When an impacted wisdom tooth starts to push through the gums, an infection can start around the top of the tooth. Infection and inflammation (swollen red gums) can cause pain, swelling and jaw stiffness.
A wisdom tooth may push nearby teeth out of their correct position and may help to cause crowding of front teeth.
Sacs of fluid called cysts can form around the tooth and may displace the tooth. The cysts can destroy bone and damage other teeth and gums.
4. Damage to nearby molars
An impacted wisdom tooth may keep pushing against molars next to it. This often leads to serious damage to both teeth.