What are impacted wisdom teeth?
BMJ Group Medical Reference
If your wisdom teeth are impacted, it means they haven't come through your gums properly. You may wonder whether you need to have these teeth taken out. But unless they are causing problems, you may be able to leave them in place.
We've brought together the best research about impacted wisdom teeth and weighed up the evidence about how to treat them. You can use our information to talk to your dentist and decide which treatment is best for you.
Your wisdom teeth are the last adult teeth to appear. There are four of them, right at the back of your mouth. But sometimes they don't come through the gums properly. This usually happens when there isn't enough space, or when the teeth are growing in the wrong direction. When this happens, they're called impacted wisdom teeth.
You may wonder if you need to have your impacted wisdom teeth taken out. But as long as these teeth are not giving you symptoms such as pain, or causing damage to other teeth, you probably do not need to have them removed. Having them taken out can be painful. And, like any surgery, the operation has risks.
Key points for people with impacted wisdom teeth
Wisdom teeth are normal adult teeth.
Sometimes they don't come through the gums properly.
When this happens, dentists describe them as impacted.
Unless your wisdom teeth are causing you trouble, you probably do not need to have them taken out.
But if they are causing pain, are damaging other teeth or your jawbone, or keep causing infections, you need to have them removed.
Your wisdom teeth
The four wisdom teeth usually come through your gums when you are in your late teens or 20s. Sometimes they come through a lot later. They got their name because they come through later than your other teeth, when you're 'older and wiser'.
Wisdom teeth are the third set of molars.
Molars are the big teeth towards the back of your mouth that you use for chewing food.
You get your first set of molars at the age of 6 or 7 and the second set between 11 and 13. Before your late teens, you'll normally have two molars on both sides of your upper and lower jaw.
Not everyone has wisdom teeth. In some people, they never appear.
When your wisdom teeth get impacted
Sometimes wisdom teeth don't come through the gums properly. This usually happens because there's not enough room for them or because they're pointing in the wrong direction. Your gums, jaw, and other teeth get in the way. In some people, all four wisdom teeth become impacted.
Wisdom teeth may be completely impacted (they are hidden below the gum). Or, they may be partially impacted (part of the tooth appears above the gum). 
Wisdom teeth are more likely to get impacted than other teeth because they emerge later than other teeth, when there is less room.
If you have small jaws, you have a higher chance of impacted wisdom teeth.