In dental terminology an "impacted" tooth refers to a tooth that has failed to emerge fully into its expected position in the oral cavity. This failure to erupt properly might occur because there is not enough room in the person's jaw to accommodate the tooth, or because the angulation of the tooth is improper. Usually this happens with Third Molars or wisdom teeth. These teeth come in behind the 2nd molars (if there is room for them and they are aligned properly), usually during a person's late teens or early twenties. Typically a person will have four wisdom teeth: upper left, upper right, lower left, and lower right.

Even though mostly the wisdom teeth are impacted, other teeth also can be impacted depending upon the spacing of teeth.