Patient-friendly definition from the DentistsDirectory.org dental glossary.
Pericoronitis is an infection of the soft tissue surrounding the crown of a partially erupted tooth — most commonly a lower wisdom tooth (mandibular third molar). When a tooth is only partially emerged through the gum, a flap of gum tissue called the operculum overlaps its crown. This flap creates a trap where food debris and bacteria accumulate in a warm, moist, poorly oxygenated environment that is almost impossible to clean adequately — ideal conditions for bacterial growth and infection.
Pericoronitis produces a characteristic set of symptoms: throbbing pain behind the last visible molar that can radiate to the ear, throat, or jaw; swelling and redness of the overlying gum tissue; a bad taste from infection discharge; and frequently, trismus — difficulty or inability to fully open the mouth because the inflamed tissue and muscle spasm limit jaw movement. Fever and swollen lymph nodes in the neck indicate the infection is spreading and require urgent attention.
Acute pericoronitis is treated by professional irrigation of the opercular flap with antiseptic solution to flush out the debris and bacteria, combined with antibiotics if there is spreading infection, fever, or lymph node involvement. This relieves the acute episode. However, pericoronitis is highly likely to recur as long as the operculum remains. Definitive treatment is usually extraction of the partially erupted wisdom tooth — removing the tissue flap (operculectomy) is an alternative but less commonly performed because the tooth often still has insufficient space to erupt fully and problems recur.