Tooth impaction

A digital X-ray film revealing an impacted permanent canine. The small tooth (bottom center) is the primary canine that has not fallen out because the permanent canine has become impacted in an abnormal direction.

Impacted and embedded teeth are the two main types of unerupted teeth found in the mouth, and can sometimes be confused with each other.

An orthopantomogram revealing four impacted Wisdom teeth.

In cases of both impacted and embedded teeth, the teeth remain below the surface of the gum and sometimes bone, rather than erupting into an exposed position within the mouth; however, the reason for the failure to erupt differs. Impacted teeth result from a situation in which an unerupted tooth is wedged against another tooth or teeth or otherwise directed so that it cannot erupt normally. In contrast, an embedded tooth is an unerupted tooth that is covered, usually completely, with bone. The former is "physically" blocked in its path of eruption, while the latter is compromised by its lack of eruptive force often without known etiology. Certain systemic and local pathologic conditions may be associated with both (i.e., cleidocranial dysostosis).

Impaction classifications

There are numerous classification systems used to identify the specific manner in which a tooth is impacted. One of the most simple distinctions made is whether a tooth is impacted completely within bone or whether it has broken through the bony cortex and is partially or completely covered in gingival tissue; the former would be termed bony impaction, while the latter would be termed soft-tissue impaction, and both classifications may present as partial or complete.^[1]

Mandibular third molars are the most commonly found unerupted teeth, while maxillary third molars are second most common.