Signs and symptoms
The signs and symptoms of pericoronitis depend upon the severity, and are variable:

Pain, which gets worse as the condition develops and becomes severe. The pain may be throbbing and radiate to the ear, throat, temporomandibular joint, posterior submandibular region and floor of the mouth. There may also be pain when biting. Sometimes the pain disturbs sleep. Tenderness, erythema (redness) and edema (swelling) of the tissues around the involved tooth, which is usually partially erupted into the mouth. The operculum is characteristically very painful when pressure is applied. Halitosis resulting from the bacteria putrefaction of proteins in this environment releasing malodorous volatile sulfur compounds. Bad taste or sour taste in the mouth from exudation of pus. Intra-oral halitosis. Formation of pus, which can be seen exuding from beneath the operculum (i.e. a pericoronal abscess), especially when pressure is applied to the operculum. Signs of trauma on the operculum, such as indentations of the cusps of the upper teeth, or ulceration. Rarely, the soft tissue around the crown of the involved tooth may show a similar appearance to necrotizing ulcerative gingivitis. Trismus (difficulty opening the mouth). resulting from inflammation/infection of the muscles of mastication. Dysphagia (difficulty swallowing). Cervical lymphadenitis (inflammation and swelling of the lymph nodes in the neck), especially of the submandibular nodes. Facial swelling, and rubor, often of the cheek that overlies the angle of the jaw. Pyrexia (fever). Leukocytosis (increased white blood cell count). Malaise (general feeling of being unwell). Loss of appetite.
Definitive treatment
If the tooth will not continue to erupt completely, definitive treatment involves either sustained oral hygiene improvements or removal of the offending tooth or operculum. The latter surgical treatment options are usually chosen in the case of impacted teeth with no further eruption potential, or in the case of recurrent episodes of acute pericoronitis despite oral hygiene instruction. Oral hygiene
In some cases, removal of the tooth may not be necessary with meticulous oral hygiene to prevent buildup of plaque in the area. Long term maintenance is needed to keep the operculum clean in order to prevent further acute episodes of inflammation. A variety of specialized oral hygiene methods are  available to deal with hard to reach areas of the mouth, including small headed tooth brushes, interdental brushes, electronic irrigators and dental floss. Operculectomy
This is a minor surgical procedure where the affected soft tissue covering and surrounding the tooth is removed. This leaves an area that is easy to keep clean, preventing plaque buildup and subsequent inflammation. Sometimes operculectomy is not an effective treatment. Typically operculectomy is done with a surgical scalpel, electrocautery, with lasers or, historically, with caustic agents (trichloracetic acid)

Tooth extraction
Removal of the associated tooth will eliminate the plaque stagnation area, and thus eliminate any further episodes of pericoronitis. Removal is indicated when the involved tooth will not erupt any further due to impaction or ankylosis; if extensive work would be required to restore structural damage; or to allow improved oral hygiene.