An impacted tooth is a tooth that is positioned against another tooth, bone, or soft tissue so that it is unlikely to fully erupt through the gums to reach its normal position in the mouth.

Wisdom Teeth (Third Molars)
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Impaction typically occurs in the third molars, also called the wisdom teeth. Wisdom teeth, which begin to develop around age 9, are most vulnerable to impaction because they are the last teeth to erupt, usually between the late teens and early 20s. By then, the jaw has stopped growing and may be too small to accommodate these four teeth.

An impacted tooth remains embedded in soft gum tissue or bone beyond its normal eruption time. The cause may be overcrowding. Other teeth may also become twisted, tilted, or displaced as the new teeth try to emerge.