In this scenario, pus may spontaneously discharge via an intra-oral sinus located over the mandibular second or first molar, or even the second premolar. Similar causes of pain, some which can occur in conjunction with pericoronitis may include:

Dental caries (tooth decay) of the wisdom tooth and of the distal surface of the second molar is common. Tooth decay may cause pulpitis (toothache) to occur in the same region, and this may cause pulp necrosis and the formation of a periapical abscess associated with either tooth. Food can also become stuck between the wisdom tooth and the tooth in front, termed food packing, and cause acute inflammation in a periodontal pocket when the bacteria become trapped. A periodontal abscess may even form by this mechanism. Pain associated with temporomandibular joint disorder and myofascial pain also often occurs in the same region as pericoronitis. J are easily missed diagnoses in the presence of mild and chronic pericoronitis, and the latter may not be contributing greatly to the individuals pain (see table).It is rare for pericoronitis to occur in association with both lower third molars at the same time, despite the fact that many young people will have both lower wisdom teeth partially erupted. Therefore, bilateral pain from the lower third molar region is unlikely to be caused by pericoronitis and more likely to be muscular in origin. Prevention
Prevention of pericoronitis can be achieved by removing impacted third molars before they erupt into the mouth, or through preemptive operculectomy.
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).