The radiographic appearance of the local bone can become more radiopaque in chronic pericoronitis. Causes
Pericoronitis occurs because the operculum (the soft tissue directly overlying the partially erupted tooth) creates a "plaque stagnation area", which can accumulate food debris and micro-organisms (particularly plaque). This leads to an inflammatory response in the adjacent soft tissues.Sometimes pericoronal infection can spread into adjacent potential spaces (including the sublingual space, submandibular space, parapharyngeal space, pterygomandibular space, infratemporal space, submasseteric space and buccal space) to areas of the neck or face resulting in facial swelling, or even airway compromise (called Ludwigs angina). Bacteria
Inadequate cleaning of the operculum space allows stagnation of bacteria and any accumulated debris. This can be a result of poor access due to limited room in the case of the 3rd molars. Pericoronal infection is normally caused by a mixture of bacterial species present in the mouth, such as Streptococci and particularly various anaerobic species. This can result in abscess formation. Left untreated, the abscess can spontaneously drain into the mouth from beneath the operculum. In chronic pericoronitis, drainage may happen through an approximal sinus tract. The chronically inflamed soft tissues around the tooth may give few if any symptoms. This can suddenly become symptomatic if new debris becomes trapped or if the host immune system becomes compromised and fails to keep the chronic infection in check (e.g. during influenza or upper respiratory tract infections, or a period of stress).
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.