All partially erupted teeth are covered by a gum flap called an operculum. This loose flap of gum creates a pocket around the crown of the erupting tooth that can trap food debris and bacteria.
As the tooth completes eruption into the mouth, the operculum moves downward to expose the complete crown of the tooth.
If the tooth does not complete an eruption, then the operculum remains unchanged. This tends to happen with wisdom teeth because of insufficient space within the jaw for the tooth to complete eruption.
If the operculum pocket is not thoroughly cleaned out, this can lead to inflammation of the gum called pericoronitis.
Acute pericoronitis usually presents with gum swelling, pain especially on chewing, jaw muscle tightness (with restricted mouth opening) and there may be pus discharging from the operculum. Pericoronitis can also be triggered by the opposing wisdom tooth biting on the operculum or a systemic infection elsewhere in the body (such as a cold or flu).
If the tooth does not complete an eruption, pericoronitis can recur in the same area. Definitive treatment is to remove the partially-erupted tooth. Coronectomy (removal of only the crown of the tooth) can be considered for cases at high risk for nerve damage.
