An impacted tooth is one that fails to erupt or only partially emerges from the gum because of an obstruction or other problem. Teeth are designed to grow beyond the gum line in childhood or early adulthood. Once impacted, they don't emerge on their own. There are a number of reasons teeth become impacted: Other teeth could be in the way, the tooth could be twisted, or the jaw could be too small to accommodate the emerging tooth.
Wisdom teeth are the third molars and last to emerge. Because they're situated at the back of the mouth where it can get pretty crowded, wisdom teeth are the most prone to becoming impacted. Nine out of 10 people have at least one impacted wisdom tooth, and most experience few if any ill effects. There can be some potential problems, though. Impacted teeth can cause pressure and pain as they push against adjacent teeth, sometimes shoving them out of alignment. If you have an attractive smile, the last thing you want is for your nice, straight teeth to shift because of the pressure exerted by an emerging wisdom tooth. Wisdom teeth can also only partially emerge, creating an opening in the gum that may allow debris to accumulate and lead to infection. In extreme cases, the bacteria growing in the pocket of a partially erupted wisdom tooth can cause jaw problems, cysts and even tumors [source: Dental Care].
There are other complications associated with impacted teeth, too. Without treatment, infections in impacted teeth can persist for months or longer. They can also spread to the roots of adjacent teeth. These infections may not be painful at first, either. This might sound like a good thing, but it's not. Any oral infection has the potential to spread via the bloodstream to other parts of the body, like the lungs, liver or heart. Although studies are ongoing, oral infections may be linked to increased risk for cardiovascular disease, diabetes and other chronic inflammatory conditions [sources: Bonine and American Academy of Periodontology].
If any of your teeth fail to emerge on schedule, a simple, dental X-ray will probably be able to determine the cause. In fact, often X-rays can help predict future impaction problems and will give you time to work with your dental professional to decide on the best approach for protecting your health and your smile.