Wisdom teeth are the teeth at the back of your mouth (the third molar teeth). They tend to come through (erupt) in the late teens or twenties.
Some wisdom teeth do not come through fully (partly erupt) and get stuck (or impacted) against nearby teeth or bone. This often leaves a flap of gum over your tooth. Others grow too long (over-erupt).
A wisdom tooth may need to be removed for one or more of the following reasons.
repeated or serious infection of the gum
a wisdom tooth can grow out too far and damage the cheek or gum
you may need an operation to move your jaw forwards or backwards
your tooth may be in a position that makes it difficult to clean properly
an orthodontist may need to make space to move other teeth backwards
you may have a cyst near or around your tooth or other jaw problems
your tooth may be in the line of a jaw fracture